Positive active material, method of manufacturing and secondary battery using the same

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a secondary battery which can repeatedly be used, and more particularly to a reliable secondary battery capable of preventing short circuit occurring due to dendrite even if the battery is repeatedly charged and discharged.

Related Background Art

Since global warming is expected to take place due to the greenhouse effect caused from an increase in CO₂ and so forth, construction of thermal power plants encounters problems. Accordingly, it has been considered feasible to perform so-called load levelling for the pupose of effectively using generators by accumulating electric power at night in secondary batteries at homes to level the load.

There arises another desire for a development of secondary battery which exhibits a high energy density for use in an electric car that does not exhaust air contamination substances. Further, development of a high performance secondary battery has been needed for use as a power source for portable equipment, such as a book-type personal computer, a word processor, a video camera and a portable telephone.

A locking chair type lithium ion battery capable of serving as the foregoing high performance secondary battery and comprising a positive electrode active material comprising lithium ions introduced into an interlayer compound thereof and a negative electrode active material comprising carbon has been developed and partially put into practical use.

However the lithium ion battery has not achieved the high energy density that is the original characteristics of the lithium battery which uses the metal lithium as the negative electrode active material. The reason why a large capacity lithium accumulator of the type that uses the lithium metal as the negative electrode has not been put into practical use is that generation of dendrite of the lithium (tree branch like crystal) which is the main cause of a short circuit cannot be prevented yet.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a lithium or lithium alloy secondary battery capable of overcoming the foregoing problems experienced with the conventional secondary batteries and exhibiting a long cycle life.

In order to overcome the foregoing problems experienced with the conventional technology, the inventors of the present invention have made energetic studies. As a result, a fact was found that generation of dendrite of lithium can be prevented by forming a film permitting ions relating to battery reactions to pass through on the surface of the negative electrode.

In a first aspect, the invention is a method of manufacturing a positive electrode active material of a lithium secondary battery, said method comprising the steps of: <ul id="ul0001" list-style="none" compact="compact"><li>forming a compound having a crystal grain size of 50 nm (500 Å) or less using a reaction selected from a group consisting of a solution reaction, a gas reaction and a melting and rapid cooling reaction;</li></ul><b>characterised in that</b> said compound is composed of a metal oxide of one or more transition metals and oxygen.

Preferred features of the first aspect of the invention are set out in dependent claims 2 to 29.

Another fact was found that employment of a positive electrode active material 13104 of a lithium secondary battery made of a compound of one or more types of transition metals having a crystal grain size of 50nm (500 Å) or less enables high capacity, large energy and long cycle life to be realized. The secondary battery of the foregoing type has a cross sectional shape schematically shown in <figref idref="f0007">Fig. 12</figref>. The same reference numerals as those shown in <figref idref="f0001">Fig. 1</figref> represent the same structures.

The main component material of the positive electrode active material has a structure of an aggregate selected from a group consisting of amorphous, microcrystal, a mixture of amorphous, microcrystal and a mixture of amorphous, microcrystal and multi-crystal.

The arrangement that the positive electrode active material of the lithium secondary battery is made of a compound of the transition metal having a structure of the aggregate selected from a group consisting of amorphous, microcrystal, a mixture of amorphous and a microcrystal and a mixture of an amorphous, a microcrystal and a multi-crystal, and oxygen and having a crystal grain size of 50nm (500 Å) or less, more preferably 20nm (200 Å) enables the following effects to be obtained: <ol id="ol0001" compact="compact"><li>(1) Since the reactive area of the positive electrode active material can be enlarged, the electrochemical reactions at the time of charge and discharge can be made smooth, and therefore the chargeable capacity can be enlarged.</li><li>(2) The introduction and the discharge of lithium ions at the time of the charge and the discharge prevent the distortion of the positive electrode active material, causing the cycle life to be lengthened.</li></ol>

It is preferable that the specific area of the positive electrode active material mainly composed of the compound of the transition metal and oxygen be 50 m²/g or more in a state before the material is formed into the positive electrode, more preferably 100 m²/g or more.

The employment of the of the transition metal oxide containing hydrogen will improve in the charge and discharge cycle characteristics.

By subjecting the positive electrode active material to a lipophilic treatment using an organic metal compound, the solid-liquid reactions between the electrolyte and the positive electrode active material can be made further smooth at the time of charge and the discharge.

The transition metal oxide is exemplified by a metal oxide such as a nickel oxide, a cobalt oxide, a titanium oxide, an iron oxide, a vanadium oxide, a manganese oxide, a molybdenum oxide, a chrome oxide or a tungsten oxide.

By employment of metal lithium having a film through which lithium ions are able to pass to form the negative electrode active material of the secondary battery, a lithium secondary battery exhibiting a long life and a high energy density can be obtained.

According to a second aspect of the present invention, there is provided a lithium secondary battery comprising a negative electrode substantially made of a negative electrode active material, a positive electrode substantially made of a positive electrode active material disposed from said negative electrode with an interposed separator; and an electrolyte or an electrolyte solution held between said negative electrode and said positive electrode, <b>characterised in that:</b><ul id="ul0002" list-style="none" compact="compact"><li>said positive electrode active material comprises as main component a metal oxide of one or more transition metals and oxygen having a crystal grain size of 50 nm (500 Å) or less.</li></ul>

Preferred features of the second aspect of the invention are set out in dependent claims 31 to 46.

BRIEF DESCRIPTION OF THE DRAWINGS

<ul id="ul0003" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a basic structural view which illustrates a secondary battery according to the present invention;</li><li><figref idref="f0001">Fig. 2</figref> is a schematic cross sectional view which illustrates a flat battery to which the present invention is applied;</li><li><figref idref="f0002">Fig. 3</figref> is a schematic cross sectional view which illustrates an example of a cylindrical battery to which the present invention is applied;</li><li><figref idref="f0002">Fig. 4</figref> is a schematic view which illustrates an example of a partial structure of a negative electrode covered with a film through which ions relating to battery reactions are able to pass;</li><li><figref idref="f0003">Fig. 5</figref> is a basic structural view which illustrates another embodiment of the secondary battery according to the present invention;</li><li><figref idref="f0003">Fig. 6</figref> is a schematic structural view which illustrates an apparatus for subjecting lithium for use in the secondary battery according to the present invention to surface treatment;</li><li><figref idref="f0004">Fig. 7</figref> is a schematic structural view which illustrates an apparatus for subjecting lithium for use in the secondary battery according to the present invention to surface treatment;</li><li><figref idref="f0004">Fig. 8</figref> is a schematic view which illustrates an effect of the present invention;</li><li><figref idref="f0005">Figs. 9A to 9H</figref> are views which illustrate examples of layer stacking patterns according to the present invention including a conductor layer, a semiconductor layer and an insulating layer between the negative electrode and the separator thereof;</li><li><figref idref="f0006">Fig. 10</figref> is another basic structural view which illustrates the secondary battery according to the present invention;</li><li><figref idref="f0006">Fig. 11</figref> is another basic structural view which illustrates the secondary battery according to the present invention; and</li><li><figref idref="f0007">Fig. 12</figref> is another basic structural view which illustrates the secondary battery according to the present invention.</li></ul>

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Structure of Battery

A secondary battery according to the present invention comprises a negative electrode, a separator, a positive electrode, an electrolyte and a collector. <figref idref="f0001">Fig. 1</figref> is a basic structural view which illustrates the secondary battery. Referring to <figref idref="f0001">Fig. 1</figref>, reference numeral 100 represents a negative collector, 101 represents a negative electrode substantially made of negative electrode active material, 102 represents a film 103 represents a positive collector, 104 represents a positive electrode substantially made of positive electrode active material, 105 represents an electrolyte solution (electrolyte), 106 represents a negative terminal, 107 represents a positive terminal, 109 represents a case for the secondary battery, and 108 represents a separator.

Negative Electrode Active Material

As the negative electrode active activating material 101, lithium or lithium alloy is used. The lithium alloy may contain one or more types of elements selected from a group consisting of magnesium, aluminum, titanium, tin, indium, boron, gallium, potassium, sodium, calcium, zinc and lead and the like.

The binding material is exemplified by polyvinyl alcohol, a cellulose material such as methyl cellulose or carboxymethyl cellulose, a polyolefin material such as polyethylene, a fluororesin such as polytetrafluoroethylene and a polyamide resin such as nylon.

The kneading solution may be an organic solvent such as ethylene glycol or water containing oxo acid salt such as sodium phosphate or the like.

The collector may be an iron plate applied with nickel plating and having apertures, a foam metal or nickel mesh or the like.

Positive Electrode

The positive electrode is formed by mixing a positive electrode active material, conductive powder and a binding material on the collector. In order to easily form the positive electrode active material, a solvent-resisting resin, such as polypropylene or polyethylene or fluororesin is used as the bonding material if necessary. In order to further easily collect electric currents, the conductive powder is mixed at the time of the formation. The material of the conductive powder is exemplified by various carbon, copper, nickel and titanium and the like.

Positive Electrode for Lithium Secondary Battery

The positive pole activating material 104 of the lithium secondary battery is made of a compound having layers through which lithium ions can be passed, the compound being prepared as set out in the appended claims. A transition metal oxide is exemplified by manganese oxide, vanadium oxide, molybdenum oxide, chrome oxide, cobalt oxide, nickel oxide, titanium oxide, iron oxide, and tungsten oxide. The transition metal element may be an element having partially shell d or shell f.

The positive pole is manufactured in such a manner that paste obtained by adding a bonding material, such as polyethylene, polypropylene or a fluororesin, to the positive pole activating material 104 is pressed against the positive pole collector 103. In order to improve the collecting performance of the positive pole, it is preferable to add conductive powder to the paste.

The conductive powder may be a carbon material such as acetylene black or metal such as copper, nickel or titanium. The collector 103 may be fiber-like, porous or mesh-shape carbon material, stainless steel, titanium, nickel, copper, platinum or gold.

Electrolyte

The electrolyte is used as it is or in the form of a solution in which it is dissolved in a solvent or after it has been solidified by adding a gelatinizing material, such as a polymer, to the solution. Generally an electrolyte solution, in which the electrolyte is dissolved in a solvent, is held in a porous separator.

The conductance of the electrolyte must be raised as much as possible because it relates to the internal resistance of the battery and considerably affects the current density at the time of the charge and the discharge. It is preferable that the conductance at 25°C be 1 x 10^-3 S/cm or higher, more preferably 5 x 10^-3 S/cm or higher.

The Negative Pole Activating Material is Lithium or Lithium Alloy.

The electrolyte is made of an acid, such as H₂SO₄, HCl or HNO₃, a salt composed of Lewis acid ion (BF₄^-, PF₆^-, AsF₆^- or ClO₄^-) or their mixture. Further, positive ions, such as sodium ions, potassium ions, tetraalkylammonium ions, and the Lewis acid ions may be used together. It is preferable that the foregoing salt is heated under lowered pressure to sufficiently dehydrate and deoxidize the salt.

The solvent of the electrolyte is exemplified by acetonitryl (CH₃CN), benzonitryl (C₆H₅CN), propylene carbonate (PC), ethylene carbonate (EC), dimethyl formamide (DMF), tetrahydrofuran (THF), nitrobenzene (C₆H₅NO₂), dichloroethane, diethoxyethane, chlorobenzene, γ - butylolactone, dioxolan, sulforan, nitromethane, dimethylsulfide, dimethylsuloxide, dimethoxyethane, methyl formate, 3 - methyl - 2 - oxydazolidinone, 2 - methyltetrahydrofuran, sulfur dioxide, phosphoryl chloride, thionyl chloride, sulfuryl chloride, dimethyl formaldehyde, γ - butyrolactone and tetrahydrofuran and their mixture.

It is preferable that the foregoing solvent be dehydrated with active alumina, molecular sieves, phosphorus pentaoxide or calcium chloride. As an alternative to this, it is preferable depending upon the type of the solvent that the solvent be distilled under presence of alkali metal in inactive gas to remove impurities and to be dehydrated.

It is preferable to gel the electrolyte solution to prevent leakage of the electrolyte solution. As the gelling material, it is preferable to use a polymer of a type which swells when it absorbs the solvent of the electrolyte solution, the gelling material being a polymer exemplified by a polyethylene oxide, polyvinyl alcohol and a polyacryl amide.

Separator

The separators (108, 208 and 308) are provided to prevent short circuits between the positive pole and the negative pole. They also act to hold the electroytic solution.

The separator must meet the following conditions. <ol id="ol0002" compact="compact"><li>(1) The separator cannot be dissolved in the electrolytic solution and must be stable with respect to the same.</li><li>(2) The separator is able to absorb a large quantity of the electrolytic solution and must exhibit satisfactory holding force.</li><li>(3) The separator must have small apertures through which lithium ions and hydroxide ions can be passed.</li><li>(4) The separator must have small apertures each having a size which is able to prevent the penetration of dendrite.</li><li>(5) The separator must be mechanically strong so as not to be broken or deformed excessively when it is wound.</li></ol>

The material that is able to meet the foregoing conditions is exemplified by a unwoven fabric or a micropore structure of glass, polypropylene, polyethylene, or fluororesin.

Also a metal oxide film having small apertures or a resin film formed by combining metal oxides may be used. If a metal oxide film in the form of a multi-layer structure is used, dendrite cannot easily pass through it and therefore an effect of preventing the short circuits can be obtained. If a fluororesin film which is a flame retardant or a glass or a metal oxide film which is a noncombustible material is used, the safety can further be improved.

Collector

Collectors 100, 103, 200 and 300 are made of fiber, porous or mesh-like carbon, stainless steel, titanium, nickel, copper, platinum or gold.

Shape and Structure of Battery

The battery is formed into a flat, cylindrical, square (rectangular) or a sheet shape battery. The spiral and cylindrical structure is enabled to have a large electrode area by winding while interposing the separator between the negative pole and the positive pole so that a large electric current can be caused to flow at the time of the charge and the discharge. The rectangular type battery enables an accommodation space for accommodating the secondary battery to be used effectively. The structure may be a single-layer structure and a multi-layer structure.

<figref idref="f0001">Figs. 2</figref> and <figref idref="f0002">3</figref> illustrate the schematic cross sectional views which respectively illustrate an example of a single-layer flat battery and a spiral and cylindrical battery. Referring to <figref idref="f0001">Figs. 2</figref> and <figref idref="f0002">3</figref>, reference numeral 201 and 301 represent negative poles covered with films, and 200 and 300 represent collectors for the negative poles 201 and 301. Reference numeral 203 and 303 represent positive pole made of the positive pole activating material. Reference numeral 304 represents a collector for the positive pole, and 206 and 306 represent negative terminals (caps for the negative poles 201 and 301). Reference numeral 207 and 307 represent outer cases (cases serving as positive pole cases and battery cases), 208 and 308 represent separators which hold the electrolytic solution, 210 and 310 represent insulating packings, and 311 represents an insulating plate.

Referring to <figref idref="f0003">Fig. 5</figref>, reference numeral 5102 represents lithium members subjected to surface treatment.

The batteries shown in <figref idref="f0001">Figs. 2</figref> and <figref idref="f0002">3</figref> are manufactured in such a manner that the separators 208 and 308 are held between the negative poles 201, 201 subjected to the surface treatment and the positive poles 203 and 303 to be placed in the positive pole cases 207 and 307 followed by injecting the electrolytic solution. Then, the negative pole caps 206, 306, the insulating packing 210 and 310 are assembled so that the batteries are manufactured.

In the case of the lithium battery, it is preferable that the preparation of the material and assembling of the battery are performed in dry air from which water has sufficiently be removed or in a dry inactive gas.

Battery Case (Outer Case)

The battery case may be a metal outer case also serving as an output terminal or a plastic resin case.

The positive pole cases 207, 307, the negative pole caps 206 and 306 are made of stainless steel, and in particular, titanium clad stainless steel or copper clad stainless steel or a steel plate applied with nickel-plating.

Although the structures shown in <figref idref="f0001">Figs. 2</figref> and <figref idref="f0002">3</figref> comprises the positive pole cases 207 and 307 also serving as the battery cases and the output terminals. The battery case may be made of metal such as aluminum or zinc, plastic such as polypropylene or a composite material of metal, glass fiber and plastic as well as the stainless steel.

Insulating Packing

The insulating packings 210 and 310 may be made of fluororesin, polyamide resin, polysulfon resin or rubber.

Cap

The capping method may be a bonding method, welding method, soldering method or a glass sealing method as well as a caulking method using a gasket such as an insulating packing.

Insulating Plate

The insulting plate 311 for insulating the inside of the battery may be made of an organic resin or ceramics.

Safety Valve

A safety valve (not shown in <figref idref="f0001">Figs. 2</figref> and <figref idref="f0002">3</figref>) using rubber, a spring or a metal ball may be used to serve as a safety means to act if the internal pressure in the battery has been raised.

The basic structure of another embodiment of the lithium secondary battery according to the present invention comprises a side opposing at least the positive pole, the side being composed of a lithium negative pole subjected to treatment using a reactive gas containing nitrogen or halogen, a separator, a positive pole activating material, electrolyte and a collector. <figref idref="f0003">Fig. 5</figref> is a basic structural view which illustrates the lithium secondary battery according to the present invention. Referring to <figref idref="f0003">Fig. 5</figref>, reference numeral 100 represents a collector for a negative electrode, 101 represents a negative electrode active material (lithium or lithium alloy), 5102 represents a surface treatment layer for the lithium portion, 103 represents a collector for the positive electrode, 5104 represents a positive electrode active material, 105 represents an electrolyte solution, 106 represents a negative terminal, 107 represents a positive terminal, 108 represents a separator, and 109 represents a battery case. In the discharge reactions, lithium ions in the electrolyte solution 105 are introduced into the interlayer of the positive electrode active material 5104. Simultaneously, lithium ions are eluted from the lithium negative electrode 101 into the electrolyte solution 105 by way of a treatment-applied surface 5102. In the charging reactions, lithium ions in the electrolyte solution 105 are, lithium metal ions are precipitated to the lithium negative electrode 101 by way of the treatment-applied surface 5102. Simultaneously, lithium in the interlayer of the positive electrode active material 5104 is eluted into the electrolyte solution 105.

Surface Treatment for Lithium Negative Electrode

The nitrogen compound for treating the surface of lithium or the lithium alloy is exemplified by nitrogen, ammonia and nitrogen trifluoride. If nitrogen is used as the nitride, it must be activated as to be formed into a plasma form by DC or high frequency discharge or by laser beam application. Also other nitrides are enabled to have improved reactivity when formed into plasma.

The halogen compound is exemplified by fluorine, chlorine, bromine, iodine, hydrogen fluoride, hydrogen chloride, hydrogen bromide, chlorine trifluoride, methane tetrafluoride, methane tetrachloride, methane trifluoride, methane fluoride trichloride, sulfur hexafluoride and boron trichloride. The inactive gas such as carbon halide must be formed into plasma as to have improved reactivity. It is preferable that the very active gas such as fluorine, chlorine, hydrogen fluoride, hydrogen chloride or chloride trifluoride be diluted with inactive gas such as argon gas or helium gas.

The nitrogen compound and the halogen compound may be mixed with each other or contain oxygen gas, hydrogen gas, argon gas, helium gas, xenon gas or the like added thereto to improve the activity of the reactive gas or to control the activity. The negative electrode may be treated with plasma of hydrogen gas or argon gas prior to treating the surface of the negative electrode so that a fresh negative electrode surface is caused to appear.

More specifically, according to the present invention, there is provided a secondary battery manufactured in such a manner that active nitrogen plasma or fluorine plasma or hydrogen fluoride is brought into contact with the surface of lithium to cause reactions to take place, an inactive thin film made of lithium nitride or lithium fluoride and allowing lithium ions to pass through is formed on the surface of lithium, and the lithium portion is used as the negative electrode. As a result, the direct contact of lithium precipitated at the time of the charge with the electrolyte solution is prevented so that the generation of dendrite at the time of the charge is prevented. Therefore, a lithium battery exhibiting a long life against the charge and discharge cycle can be obtained. Further, the application of the foregoing treatment to the surface of lithium prevents the reactions between lithium and water. Further, handling can be made easier.

It is preferable that the thickness of the treatment layer to be formed on the surface of lithium ranges from 1nm (10 Å) to 1 µ, more preferably 5nm to 50nm (50 Å to 1000 Å.) The thickness is adjusted by the reaction time or the concentration of the reaction gas.

It is preferable that the concentration of nitrogen atoms or halogen atoms in the treatment layer formed on the surface of lithium be gradually lowered from the surface to the inside portion of lithium.

Positive Pole Activating Material

The positive pole activating material 5104 is be a material into which lithium can be introduced into the interlayer thereof, the material being a metal oxide such as a nickel oxide, cobalt oxide, titanium oxide, iron oxide, vanadium oxide, manganese oxide, molybdenum oxide, chrome oxide or tungsten oxide.

In order to make easier the formation of the positive pole activating material, solvent-resisting resin, such as polypropylene, polyethylene or fluororesin is used as a bonding material if necessary. In order to further facilitate collection of electric current, it is preferable to mix conductive powder at the time of molding the positive active material. The conductive powder may be carbon black, copper, nickel or titanium.

<figref idref="f0004">Fig. 8</figref> illustrates an example a pattern of stacked layers according to the present invention in which a conductive layer, a semiconductor layer and an insulating layer are formed between the negative pole and the separator. Referring to <figref idref="f0004">Fig. 8</figref>, reference numeral 001 represents a negative pole, 002 represents a dendrite, 003 represents the conductive layer or the semiconductor layer, 004 represents a separator, 005 represents an insulating layer, 006 represents an electrolytic solution, and 007 represents a positive pole.

<figref idref="f0004">Fig. 8</figref> is a schematic view which illustrates an effect of the present invention in an example in which the insulating layer through which lithium ions can be passed and a conductive layer are stacked on the surface of the lithium negative pole.

When the charging mode, lithium is precipitated on to the negative pole 001. At this time, a portion in which the current density is high is locally generated on the negative pole 001 depending upon the projections and pits of the surface and upon the thickness of the insulating film. Lithium is selectively deposited, causing the dendrite 002 to grow. With proceeding of the charging or discharging cycle, the dendrite 002 reach the conductive layer 003. When a short circuit state between the dendrite 002 and the conductive layer 003 is realized, the current density at the negative pole is lowered at the time of the charge. Therefore, the further growth of the dendrite 002 is prevented, and therefore penetration of the dendrite 002 through the separator 004 to reach the positive pole 007 can be prevented.

By covering the negative pole with the ion permeable insulating layer 005, active lithium precipitated at the time of the charge cannot easily react with the electrolytic solution. Therefore, the generation of the growth of the insulating film can be prevented.

<figref idref="f0005">Figs. 9A to 9H</figref> illustrate various examples in which one or more types of layers selected from the ion permeable conductor, semiconductor and insulating material are formed between the negative pole and the separator. Reference numerals shown in <figref idref="f0005">Figs. 9A to 9H</figref> are the same as those shown in <figref idref="f0004">Fig. 8</figref>. The present invention is not limited to the structure shown in <figref idref="f0005">Figs. 9A to 9H</figref>.

It is preferable that the conductive layer to be formed between the negative pole and the separator be made of carbon, Ni, Ti, Pt, Al, Pb, Cr, Cu, V, Mo, W, Fe, Co, Zn or Mg, more preferably made of carbon, Ni or Ti.

If the semiconductor layer is formed in place of the conductive layer, a similar effect obtainable from the conductive layer can be obtained. If the semiconductor layer is employed, the current density at the time of the growth of dendrite is higher than that in the case where the conductive layer is formed. However, the conductivity is lowered as compared with the case where the conductive layer is formed. Therefore, an advantage can be realized that the easy conduction with the positive pole is prevented.

The semiconductor layer may be made of diamond, Si, nickel oxide, copper oxide, manganese oxide, titanium oxide, zinc oxide, zirconium oxide, tungsten oxide, molybdenum oxide or vanadium oxide.

The insulating layer may be made of a halide such as lithium fluoride or magnesium fluoride, a nitride such as silicon nitride, a carbide such as silicon carbide, or a polymer such as polyethylene, polypropylene or fluororesin.

The forming method and materials of the conductive layer, the semiconductor layer, the insulating layer and the composite layer will now be described. When lithium is used, the following two desires must be met.

If water is left in the raw material, water and lithium react with each other. Therefore, water must be previously removed by a method of dehydration using active alumina, molecular sieve, phosphorus pentaoxide or calcium chloride. If a solvent is used, it is sometime preferable that the solvent be distilled under presence of alkali metal in inactive gas to remove impurities and to be dehydrated.

The temperature at which the foregoing layer is applied to the surface of the negative pole must be lower than a level at which the negative pole activating material is melted.

Conductive Layer

As a typical example of the conductive layer, manufacturing method of carbon conductive layer or a metal conductive layer made of, for example, Ni or Ti, will now be described.

Carbon

The form of the carbon crystal is categorized to crystal, amorphous, and a mixture of them. The carbon to be applied may be carbon powder or carbon fiber or a carbon paper sheet or the like obtainable by paper machining.

The surface of the negative pole can be covered with carbon by any one of the following methods. <ol id="ol0003" compact="compact"><li>(1) A solution obtained by uniformly dispersing carbon powder or carbon fiber in an organic solvent such as toluene or xylene is, under inactive atmosphere of Ar, applied to the surface of the negative pole by a spraying method, screen printing method, a coater method or a dipping method followed by drying the solution, and then carbon are pressed against the surface.</li><li>(2) The carbon paper is stacked on the surface of the negative pole, and then the carbon is pressed against the surface.</li><li>(3) A vacuum evaporation method such as sputtering using carbon as the target is performed so that the surface of the negative pole is covered with carbon.</li><li>(4) A CVD (Chemical Vapor Deposition) method is performed under the presence of an organic compound which is the raw material of carbon so that the negative pole is covered with carbon.</li></ol>

In the foregoing coating method, the carbon powder or the carbon fiber must be pressed against the surface so that the contact is improved. The pressing work is performed by using a pressing machine or a roller press. The temperature at the time of the pressing work must be lower than a level at which the negative pole activating material is melted. It is preferable that the thickness of the coating range from 10 to 100 µm, more preferably from 50 µm or thinner in order to prevent reduction of the quantity of the contained negative pole activating material.

The pressing method to be performed after the carbon paper has been stacked may be a method using a pressing machine or a roller press, a method in which the positive pole plate and the negative pole plate are wound while interposing the separator, and a method in which winding pressure or stacking pressure is applied while interposing the carbon paper at the time of stacking the carbon paper. The latter method is able to eliminate a process of previously pressing the carbon paper against the negative pole and the carbon paper can be pressed in the winding or the stacking process. It is preferable that the carbon paper having a thickness ranging from 150 to 300 µm be pressed to have a thickness ranging from 75 to 150 µm.

The sputtering coating method is performed in such a manner that carbon is used as the target in an inactive atmosphere of argon and DC or RF discharge is performed so that the surface of the negative pole is covered with carbon.

The raw material of the CVD carbon coating method may be saturated hydrocarbon such as methane, unsaturated hydrocarbon such as acetylene, ethylene, propylene or benzene, carbon monoxide, alcohol or acetone. The exciting method is exemplified by a method using plasma, laser or heating filament. It is preferable that the thickness of the carbon applied be 1 µm or thinner, more preferably 100nm (1000 Å).

In the case of the plasma CVD method, the power source for the glow discharge may be a high frequency or a DC power source. The high frequency source may be a usual band source such as radio frequency (RF), VHF or microwave source. The wavelength of the radio waves is typified by 13.56 MHz, while that of the microwave is typified by 2.45 GHz.

If the laser CVD is employed, an ultraviolet ArF eximer laser or infrared ray CO₂ is used as the laser beam source.

Metal Such as Ni or Ti

The metal such as Ni or Ti is applied to the surface of the negative pole by a sputtering method as is employed to apply carbon, a CVD method, an electron beam evaporation method or a cluster ion beam evaporation method.

The target for use in the sputtering method may be Ni or Ti or the like. When a composite film is formed, two or more kinds of targets are used to perform either or both of the targets are subjected to the sputtering process. The sputtering method must be performed under an inactive atmosphere of argon similarly to carbon.

The CVD coating method employs the following materials as the raw materials.

As the raw material for Ni and Ti, a solution in which organic metal such as acetylacetone complex of nickel (or titanium) is dissolved in non-water-soluble solvent such as hexane, acetone or toluene or a solution in which a halide such as nickel chloride (or titanium) is dissolved in a non-water-soluble solvent such as ethanol is subjected to bubbling in a carrier gas (hydrogen or the like) and then the solution is introduced into the CVD reaction chamber to cause the CVD reactions to take place so that coating is performed.

When a composite film of Ni and carbon is formed, a hydrocarbon such as methane is used together with a metal compound.

Semiconductor Layer

The semiconductor layer is exemplified by diamond, Si, nickel oxide, copper oxide, cobalt oxide, manganese oxide, titanium oxide, zinc oxide, zirconium oxide, tungsten oxide, molybdenum oxide or vanadium oxide. The coating method may be a sputtering method, an electron beam evaporation method, a plasma CVD method, a light CVD method, a laser CVD method or a heat CVD method.

Si

As the target for use in the sputtering method, Si or the like is used.

In the CVD method, the raw material for Si may be hydroxide gas such as SiH₄ or Si₂H₆, fluorine gas such as SiHF₃, SiH₂F₂ or SiH₃F, or a chlorine gas such as SiHCl₃, SiH₂Cl₂ or SiHCl₃. If the foregoing raw material is in the form of liquid, it is heated as to be in the form of vapor or subjected to bubbling by a carrier gas before it is introduced. If a composite film of Si and carbon material is formed, hydrocarbon such as methane is used together with the foregoing gas. A compound comprising carbon, P or B may be adequately mixed.

Oxide such as Nickel Oxide and Titanium Oxide

The nickel oxide and titanium oxide can be prepared by a sol-gel method in which alkoxide such as nickel or titanium or organic metal is dissolved in alcohol and then it is hydrolyzed, an anodic oxidation method in which a solution in which nickel salt or titanium salt is dissolved is electrolyzed, or a CVD method or an electron beam evaporation method to introduce oxygen gas into the reaction chamber.

Insulating Layer

As the insulating layer, a halide, a nitride, a carbide or resin such as polyethylene (PE), polypropylene (PP) or fluororesin is used. As the coating method, a sputtering method, a plasma CVD method or a coating method is used.

Other resins may be used such that a resin obtained by gasifying a monomer of an organic polymer and by plasma polymerizing it or a resin obtained by sputtering an organic polymer or a film of an organic polymer may be used. In this case, the resin member must have small aperture through which ions can be passed and must not react with the electrolytic solution.

Nitride

In the sputtering method, a target comprising nitride exemplified by silicon nitride or lithium nitride is used. As an alternative to this, Si or Li is used as the target, nitrogen gas or ammonia is used as the reaction gas and sputtering is performed in the foregoing state.

PE and PP

In the plasma CVD method, SiH₄ or Si₂H₆ and ammonia, nitrogen gas or NF₃ are used together as the raw materials.

In the sputtering method, a PE or PP target is used to perform sputtering to cover the insulting layer.

In the plasma polymerization method, ethylene is used as the raw material in the case of PE, while propylene is used in the case of PP.

Fluororesin

In the sputtering method, the target comprises a polymer or a copolymer such as polytetrafluoroethylene, polytrifluoroethylene, vinyl fluoride, vinylidene fluoride or dichlorodifluoroethylene.

As the raw material gas for use in the plasma polymerization method, tetrafluoroethylene, trifluoroethylene, vinyl fluoride, vinylidene fluoride or dichlorofluoroethylene is used.

A fluororesin film having micropores can be used.

Composite Layer

The composite layer is selected from a group consisting of the foregoing conductor, semiconductor and insulating material. By using two or more types or raw materials, the composite layer is formed by a sputtering method or a CVD method. As an alternative to this, two or more types of powder selected from a group consisting of conductor powder, semiconductor powder and insulating material powder are melted in a melted or dissolved resin so that the film for use as the composite film is manufactured.

Another structure may be employed as a preferred structure in which the concentrations (content) of the conductor, semiconductor and the insulating material in the composite layer are changed continuously or discontinuously in the direction of the thickness of the layer.

The apertures in the layer can be formed in such a manner that: an electrolyte is mixed with the raw material at the time of applying the conductor, semiconductor and the insulating material by the sputtering method or the CVD method to add the electrolyte into the conductor, semiconductor and the insulating material. The foregoing electrolyte is eluted into the electrolytic solution of the battery so that micropore structures are formed in the conductor, semiconductor and the insulating material. Since lithium ions and hydroxide ions can easily be introduced and discharged in the micropores, the charging and discharging efficiencies can be improved. Since the pore has a small size, the growth of the dendrite can be prevented, and therefore the life against the charging and discharging cycle can be lengthened.

Stacked Structure

The conductor, semiconductor and the insulating material layers may be formed into a single layer or a multi-layer composed of two or more layers.

The stacking method comprises a step of stacking a film selected from the group consisting of the conductor, semiconductor and the insulating material between the negative pole and the separator. The film is stacked on the surface of the negative pole, or stacked between the negative pole and the separator in a non-contact manner or stacked on the surface of the separator. As an alternative to this, the negative pole or the separator or a substance through which ions can be passed may be used as the base on which the conductor, semiconductor and the insulating material are stacked by a sputtering method or a CVD method.

Thickness

The optimum thickness of the single, multi-layer or the composite layer composed of the one or more types of layers selected from the group consisting of the conductor, semiconductor and the insulating material differs depending upon the void ratio, the aperture distribution, the material of the layers and the number of layers. If the material includes a large volume of gaps as the polymer material, it is preferable the thickness be 10 µm or thinner, more preferably 1 µm or thinner. If a precise material such as the inorganic compound is used, it is preferable to make the thickness to be 1 µm or thinner, more preferably 100nm (1000 Å) or thinner.

Multi-Layer Metal Oxide

The multi-layer metal oxide 10102 must contain one or more types of materials selected from a group consisting of alumina, titanium oxide, silica, selium oxide, zirconia oxide, magnesium oxide, chrome oxide, calcium oxide, tin oxide, indium oxide and germanium oxide.

The multi-layer metal oxide film is formed by molding a bimolecular film in a mold. By forming the metal oxide film by using the bimolecular film, a metal oxide film having small apertures and a large specific area and formed into a multi-layer film structure can be obtained.

Method of Preparing Multi-Layer Metal Oxide

The preparation is usually in such a manner that: a sol in which very fine particles of the metal oxide is, in a colloid manner, dispersed in a solvent, such as water, is added to a supersonic dispersion solution of water or buffer solution of a film forming compound for forming a bimolecular film selected depending upon the type of the sol and upon the surface charge so that a uniformly-dispersed solution is prepared; then it is developed on a fluororesin film or a glass plate followed by developing the solution; and a cast film is manufactured. If the uniformly-dispersed film cannot be obtained, any one of the following methods is employed: <ol id="ol0004" compact="compact"><li>(1) A cast film is formed by adding a low-melting point organic solvent, such as alcohol, chloroform, acetone or tetrahydrofuran, is added to the film forming compound and dispersing the materials, and then water or a buffer solution is added to the solution from which the solvent has been gradually evaporated, and then the mixture is dispersed with ultrasonic waves.</li><li>(2) Water or a buffer solution is added to the cast film described in (1), and the material is heated to a level higher than the phase transition temperature of the film.</li><li>(3) The film forming compound is dissolved in an organic solvent, such as diethylether or ethylalcohol, and the solution is injected into water and a buffer solution.</li></ol>

As a method of obtaining the bimolecular film which serves as the mold of the film shape of the metal oxide, the mechanical strength can be improved by any one of the following methods: <ol id="ol0005" compact="compact"><li>(a) The film forming compound is impregnated into a porous polymer film to form the bimolecular solid film.</li><li>(b) A hydrophobic polymer or a hydrophilic polymer and the film forming compound are dissolved in a solvent, and the solution is developed so that a cast film is obtained.</li><li>(c) A solution of a polymer electrolyte having a charge opposing that of the ionic film forming compound is mixed with a solution in which the ionic film forming compound is dispersed so that sedimentation of polyion complex is obtained, and then the polyion complex is dissolved in an organic solvent followed by developing it so that the cast film is obtained.</li></ol>

Alternatively, any one of the following methods may be employed: a chloric acid (surface active agent) method which is used at the time of preparing ribosome; a freezing-melting method; an inverse-phase evaporation method; and a macro-ribosome preparation method.

The film forming compound may be a compound having both hydrophobic group and a hydrophilic group (substance having amphipathic property) is used. The film forming compound may be an ammonia compound, an anion compound, a nonion compound and a polymerizable compound depending upon the molecular structure. The hydrophobic group of the film forming compound is categorized to a hydrocarbon, fluorine carbide, unsaturated hydrocarbon, and unsaturated fluorine carbide. A material containing a chromophore structure introduced thereto in order to improve the molecular orientation in the film forming compound may be used.

The film forming compound is exemplified by p - octyloxyaniline hydrochloride, p - (octyloxy) - p' - hydroxyazobenzene, p - (10 - octyloxy) - p' - octyloxyazobenzene, dodecyl - N - [p - (p - (10 - bromodecyloxy)phenylazo}benzoil]L - alaninate, L - glutamic acid didodecylester hydrochloride, N - [11 - bromoundecanoyl] - L glutamic acid didodecylester, dimethyldihexadecylammonium bromide, N - [β - (trimethylamino) ethyloxybenzoyl]didodecyl - L - glutamic acid bromide, dioctadecylmethyldimethylammomonium bromide, N - [11 - hydroxyundecanoyl] - L - glutamic acid ditetradecylester, N - [11 - phosphoroundecanoyl] - L - acid ditetradecylester, 1, 2 - bis (hexadecyloxycarbonyl) ethane - 1 - sulfonic acid sodium, N - [(2 - oxo - 1, 3, 2 - oxazaphosphoryl) - 11 - oxadodecanoyl] - L - glutamic acid didoecylester, N - [(2 - trimethylammonio - ethylphosphonate)undecanoyl] - L - glutamic acid didodecylester, N - [(2 - ammomonio - ethylphosphonate)undecanoyl] - L - glutamic acid didodecyl ester and 1, 3 - hexadecyl - 2 - polyethylene glycolylglyceline.

It is preferable that the surface of the multi-layer metal oxide film of a non-water-soluble battery of a type comprising the negative pole activating material which is lithium is subjected to lipophillic treatment using an organic metal compound such as a silane coupling material or titanate coupling agent.

In order to lower the current density at the leading portion of the dendrite at the time of the charge and to prevent the growth of dendrite, the surface of the multi-layer metal oxide film on the negative pole side may be applied with a conductive material by evaporation or plating.

Very Fine Particle Sol of Metal Oxide

The dispersed sol of very fine particles of the metal oxide is usually obtained by an acid, a base and water are added to an alcohol solution of an organic metal compound such as metal alkoxide as to be hydrolyzed to form colloid of the very fine particles of the metal oxide. The dispersion medium of the very fine particle sol is obtained by substituting to an organic solvent if necessary.

The alkoxide is typified by tetramethoxysilane, tetraethoxysilane, aluminum isopropoxide, and titanium isopropoxide. Another metal organic compound such as acetyl acetone complex salt, alkyl metal compound, acetylacetone metal salt, naphthenate metal salt or octylate metal salt may be used.

The very fine particles of the metal oxide can be obtained by another method for obtaining the same from the gas phase reaction of the vapor of the organic metal compound or the metal. The obtained very fine particles of the oxide are dispersed in a solvent so that a dispersed sol is prepared.

Since the negative pole activating material is lithium or lithium alloy, lithium ions relate to the battery reactions.

By covering the surface of the positive pole 104 of the battery with a film 12102 which is made of an insulating material or a semiconductor through which ions relating to the battery reactions can be passed, dendrite of lithium grown from the negative pole 101 through the separator 108 during the repetition of the charge and the discharge are not substantially brought into contact with the conductor or a collector in the positive pole 104. As a result, short circuits in the battery can be prevented, and therefore the life of the secondary battery can be lengthened. Further, the safety can be improved.

Covering of Positive Pole of Secondary Battery

As the insulating material of the coating material of the positive pole of the secondary battery, any one of the following materials may be used which is selected from a group consisting of a polymer of the derivative of a large ring compound, a polymer of the derivative of an aromatic hydrocarbon, fluororesin, silicon resin, titanium resin, polyolefin, inorganic oxide, nitride, carbide and halide. It is effective for the positive pole of the lithium secondary battery to be covered with the polymer of the derivative of the large ring compound, the polymer of the derivative of the aromatic hydrocarbon or the fluororesin.

Polymer of Derivative of Large Ring Compound

The large ring compound is a ring compound of a type comprising hetero-atoms of one or more types selected from a group consisting of oxygen, nitrogen, sulfur and phosphorus. The large ring compound is a ring polyether having hole each having a radius larger than the radius of the lithium ion. The large ring compound has one or more structures selected from a group consisting of ring polyamine, ring polythioether, azacrown ether, ring thioether, thiocrown ether, cryptand, cyclam, nonactine, variomicine, thyracrown which is a crown ether containing silicon atoms, cyclodextrin, cyclofan, phthalocyanin and porphyrin compound.

The surface of the positive pole is covered with the large ring compound by any one of the following methods. <ol id="ol0006" compact="compact"><li>a. A polymer solution obtainable from polymerization of the derivative of the foregoing large ring compound is applied by a coating method such as dipping, spraying, screen-printing or coating application method.</li><li>b. A mixture in which the derivative of the large ring compound is mixed with the polymer serving as the binder is applied and then crosslinked to form the film.</li><li>c. The derivative of the large ring compound is used as a monomer to be dissolved in an electrolytic solution, and then an electric field is applied to electrolyze and polymerize the material so that the film is formed on the surface of the positive pole.</li><li>d. The molded positive pole is immersed in a solution of the derivative of the large ring compound, which anion-polymerizes, so that the polymer film is formed.</li><li>e. A polymer obtainable by heating and condensing the large ring compound having an aromatic ring and formaldehyde in a formic acid is applied.</li><li>f. The film is formed by sputtering of a polymer of the large ring compound or the derivative of the large ring compound or by plasma-polymerizing the large ring compound.</li></ol>

An electrolyte may be mixed at the time of forming the film. As a result, the wettability between the electrolytic solution and the film can be improved, causing ions to easily pass through the film.

The polymer for use as the coating solution may be poly [(dibenzo - 18 - crown - 6) - co - formaldehyde] or the like. The coating polymer can be newly formed by the following polymerizing reactions: a large ring compound having a carboxylic group or an amino group or a hydroxyl group at the terminal group thereof is condensed and polymerized so that polyamide is obtained if the carboxylic group and the amino group react with each other. If the carboxylic group and the hydroxyl group react with each other, polyester can be obtained. The vinyl compound of the large ring compound or diene of the large ring compound can be obtained in the form of an addition polymer by radical polymerization, cation polymerization or anion polymerization. The starting material in the radical polymerization may be azobisisobutyronitryl (AIBN), benzoylperoxide (BPO) or t - butylhydroperoxide. A starting material for the cation polymerization is exemplified by an acid such as H₂SO₄, H₃PO₄, HClO₄, CCl₃CO₂H and Friedel-Crafts catalyzer such as BF₃, AlCl₃, TiCl₄ or SnCl₄. A large ring compound having an aromatic ring can be polymerized by dehydrogenation in which the Friedel-Crafts catalyzer and an oxidizer are combined to each other. A starting material for the anion polymerization may be an alkaline metal compound or an organic metal compound.

As the monomer of the large ring compound for use in the polymerization may be crown ether/(+) - 18 - crown - 6 - tetracarboxylic acid, 1, 5, 9, 13, 17, 21 - hexathiacyclotetrakosan - 3, 11 - 19 - triol, 1, 5, 9, 13 - tetrathiacyclohexadecan - 3, 11 - diol, 1 - aza - 12 - crown - 4, 1 - aza - 15 - crown - 5, 1 - aza - 18 - crown - 6, 1, 4, 10, 13 - tetraxyso - 7, 16 - diazocyclooctadecan, 1, 4, 10 - trioxa - 7, 13 - diazacyclopentadecan, or 6, 8 - dioxabicyclo [3. 2. 1] - oxtane - 7 - on. As an alternative to this, dibenzocrown ether can be used.

In the foregoing polymerization, a copolymer of two more types of derivatives of the large ring compounds or a copolymer of the large ring compound and another monomer may be used as well as the polymer of the derivatives of the large ring compounds. A polymer obtainable by introducing the derivative of the large ring compound into a polymer by substitution may be employed.

When a battery is manufactured, a polymer must be selected so as not to be dissolved in the solvent of the electrolytic solution or the polymer crosslinking reactions are caused to proceed so as not be dissolved in the electrolytic solution.

The derivative of the large ring compound having, at the terminative group thereof, carboxylic group or amino group or a hydroxyl group or having a vinyl bond or a diene bond and a crosslinking material are mixed in the polymer serving as the binder, and then the mixed material is hardened. An accelerating material may be mixed at this time. The crosslinking material is selected from a group consisting of diisocyanate, a polyisocyanate prepolymer, block isocyanate, an organic peroxide, polyamine, oximes, a nitroso compound, sulfur, a sulfur compound, selene, a magnesium oxide, a lead oxide and a zinc oxide. The organic peroxide is exemplified by di - cumyl - peroxide, 2, 5 - dimethyl - 2, 5 - di - (t - butyl - peroxy) hexane, 1, 3 - bis - (t-butyl - peroxy isopropyl) benzene, 1, 1 - bis - (t-butyl - peroxy) - 3, 3, 5 - trimethyl - cyclohexane, n - buty - 4, 4 - bis - (t - butylperoxy) valelate, 2, 2 - bis - (t - butyl - peroxide) butane, t - butyl - peroxy - benzene, and vinyl - tris - (t - butyl - peroxy) silane. As an accelerating agent, a guanidine, aldehyde - amine; aldhyde-ammonia, thiazol, sulfonamide, thiourea, thiuram, dithiocarbamate, xanthate accelerating agent is used.

Another coating method using the binder polymer is exemplified by a method in which a mixture of the large ring compound and the binder polymer is applied, and then radial rays, electron rays or ultraviolet rays are applied to cause the applied material to be crosslinked.

As a method for covering the positive pole by the electro-polymerization, a monomer, such as dibenzocrown ether, is mixed in the electrolytic solution, and then the electrolytic polymerization is performed while using the negative pole activating material or the conductive matrix as an anode. The solvent of the electrolytic solution is exemplified by acetonitryl (CH₃CN), benzonitryl (C₆H₅CN), propylene carbonate (PC), dimethylformamide (DMF), tetrahydrofuran (THF), nitrobenzene (C₆H₅NO₂), dichloroethane, diethoxyethane, chlorobenzene, γ - butyrolactone and dioxolan and their mixture.

It is preferable that the solvent be dehydrated with active alumina, molecular sieve, phosphorus pentaoxide or calcium chloride.

The supporting electroyte is an acid, such as H₂SO₄, HCl or HNO₃ or salt composed of monovalent metal ion (Li⁺, K⁺, Na⁺, Rb⁺ or Ag⁺) or tetraammonia ion (tetrabutyl ammonia ion (TBA⁺) and tetraethyl ammonia ion (TEA⁺)) and Lewis acid ion (BF₄^-, PF₆^-, AsF₆^- or ClO₄^-). It is preferable that the foregoing salt is refined by re-crystallization or it is heated under lowered pressure to sufficiently dehydrate and deoxidize the salt.

As the monomer, crown ether/benzo - 15 - crown - 5, crown ether/benzo - 18 - crown - 6, crown ether/N - phenylaza - 15 - crown - 5, crown ether/dibenzo - 18 - crown - 6, crown ether/dibenzopyridino - 18 - crown - 6, crown ether/dibenzo - 24 - crown - 8, 1, 13 - bis (8 - quinolyl) - 1, 4, 7, 10, 13 - pentaoxatridecan, 5, 6 - benzo - 4, 7, 13, 16, 21, 24 - hexaoxa - 1, 10 - diazabicyclo [8. 8. 8] - hexakosan, 5, 6 - 14, 15 - dibenzo - 4, 7, 13, 16, 21, 24 - hexaoxa - 1, 10 - diazabicyclo [8. 8. 8] - hexakosan, bis [(benzo - 15 - crown - 5 - ) - 15 - ilmethyl] pimelate, crown ether/dibenzo - 30 - crown - 10, N, N' - dibenzyl - 1, 4, 10, 13 - teraoxa - 7, 16 - diazacyclooxtadecan, dilithiumphthalocyanin, 4' - nitrobenzo - 15 - crown - 5, 3, 6, 9, 14 - tetrathiabicyclo [9. 2. 1] tetradeca - 11, 13 - diene and their mixture.

Since the performance of the battery deteriorates if the polymer film for covering the surface of the negative pole activating material is dissolved in the electrolytic solution, it is preferable to be crosslinked.

It is preferable that the thickness of the film to be formed on the surface of lithium ranges from 1nm (10 Å) to 100 µ, further preferably ranges from 5nm (50 Å) to 10 µ. The optimum thickness of the film differs depending upon the density or the void ratio of the film and considerably differs depending upon the type of the electrolytic solution. The thickness of the film can be adjusted by changing the concentration of the main material in the coating liquid for forming the film.

Polymer of Derivative of Aromatic Hydrocarbon

As the derivative of the aromatic hydrocarbon for forming the charge moving complex is one or more types of derivatives selected from a group consisting of naphthalene, anthracene, phenanthrene, naphthacene, pyrene, triphenylene, perillene, picene, benzopyrene, coronene and ovalene.

The polymer for use to form the coating material can be prepared by polymerization or copolymerization of vinyl monomer, monomer of acetylene derivative or dicarboxylic acid and diamine, and dicarboxylic acid and glycol. The polymerization of the vinyl monomer can be performed by radical or ion polymerization. The monomer of the acetylene derivative can be polymerized while using a chloride of tungsten as a catalyzer. The dicarboxylic acid and diamine can be polycondensed and the dicarboxylic acid and glycol can as well as be polycondensed.

The monomer of the aromatic derivative for forming the polymer is exemplified by 2 - vinyl naphthalene, 2 - vinyl pyridine, 9 - vinyl anthracene, 9, 10 - anthracene dipropionic acid, 9, 10 - bis (phenyl ethyl) anthracene and 5, 12 - bis (phenyl ethynyl) naphthalene.

A starting material for the radical polymerization is exemplified by azobisisobutylonitryl (AIBN), benzoylperoxide (BPO) and t - butylhydroperoxide. A starting material for the cation polymerization is exemplified by an acid such as H₂SO₄, H₃PO₄, HClO₄, CCl₃ or CO₂H and Friedel-Crafts catalyzer such as BF₃, AlCl₃, TiCl₄ or SnCl₄. A large ring compound having an aromatic ring can be polymerized by dehydrogenation in which the Friedel-Crafts catalyzer and an oxidizer are combined to each other. A starting material for the anion polymerization may be an alkaline metal compound or an organic metal compound.

As an alternative to the foregoing method, a polymer into which an aromatic group can be obtained by subjecting the side chain of each polymer to a substitution reaction with a derivative of an aromatic compound. Another method may be employed in which an electrolytic polymerization reaction is caused to take place in an electroytic solution containing a monomer mixed therein to form directly a polymer of an aromatic compound on the surface of positive pole.

When the surface of the positive pole is applied with a coating by using the foregoing polymer solution, it is preferable to use a polymer solution dehydrated and deoxidized sufficiently in inactive gas dehydrated sufficiently. It is preferable to use a solvent in the foregoing solution which has been dehydrated with active alumina, molecular sieve, phosphorus pentaoxide or calcium chloride. As an alternative to this, it is preferable depending upon the type of the solvent that the solvent be distilled under presence of alkali metal in inactive gas to remove impurities and to be dehydrated.

An electrolyte may previously be mixed when the foregoing film is formed. It leads to a fact that wettability between the electrolytic solution and the film can be improved, causing ions to easily pass through the film.

Since the performance of the battery deteriorates if the polymer coating film is dissolved in an organic solvent of the electrolyte, it is preferable to be crosslinked in such a manner, for example, ultraviolet rays, electron rays or radial rays are applied or a crosslinking material, such as a radical generating agent, is used.

Fluororesin

The fluororesin for covering the surface of the positive pole is exemplified by ethylene tetrafluoride-ethylene copolymer, ethylene tetrafluoride chloride, ethylene tetrafluoride - per - fluoroalkylvinyl ether copolymer, ethylene tetrafluoride - propylene hexafluoride copolymer, vinylidene fluoride resin, vinyl fluoride resin, and ethylene tetrafluoride resin. Since the foregoing materials are not dissolved in a solvent, it is preferable to employ sputtering or plasma polymerization to cover the surface of the positive pole with the fluororesin.

Among the fluororesins, those having an ether bond are able to facilitate the surface covering because they can easily be dissolved in a solvent and to improve the affinity with lithium ions. The fluororesin having the ether bond is exemplified by: a copolymer of ethylene fluoride and vinyl monomer such as vinyl ether, dioxysol, dioxyne or dioxycene having an ether bond or dienemonomer derivative or a copolymer with a vinyl monomer, such as vinyl ether, dioxysol or dioxyne, dioxycene having a fluorized ether bond with a diene compound, such as ethylene. The fluoroethylene may be a fluoroethylene derivative such as tetrafluoroethylene, chlorotrifluoroethylene, vinylidenefluoride or vinyl fluoride. The fluoroethylene copolymer containing the ether bond can be polymerized by a solution, suspension, block or emulsion polymerization. As a starting material, a peroxide, alkyl boron, light or radial rays may be employed.

The fluororesin can be coated on the surface of the positive pole by any one of the following methods. <ol id="ol0007" compact="compact"><li>a. A solution of the fluororesin is applied by spraying, screen printing, by using a coater or by dipping.</li><li>b. The fluororesin is directly coated to the surface of the positive pole by a vacuum evaporation method such as sputtering.</li><li>c. A polymer film is directly formed by plasma polymerization under an atmosphere of monomer which is the raw material for the fluororesin.</li></ol>

If the lithium surface is coated by using the fluororesin solution, it is preferable to use, in an inactive gas dehydrated sufficiently, a fluororesin solution dehydrated and deoxidized sufficiently. It is preferable to use a solvent in the foregoing solution which has been dehydrated with active alumina, molecular sieve, phosphorus pentaoxide or calcium chloride. As an alternative to this, it is preferable depending upon the type of the solvent that the solvent be distilled under presence of alkali metal in inactive gas to remove impurities and to be dehydrated.

An electrolyte may previously be mixed when the foregoing film is formed. It leads to a fact that wettability between the electrolytic solution and the film can be improved, causing ions to easily pass through the film.

Since the performance of the battery deteriorates if the fluororesin film is dissolved in an organic solvent of the electrolytic solution, it is preferable that the film is crosslinked.

As an alternative to the foregoing method of coating the surface with the fluororesin solution having the ether bond, another method may be employed in which ethylene fluoride and vinyl monomer are used as the main raw material as to be plasma-polymerized so that the surface is covered. In order to easily cause the plasma polymerization to take place easily or to improve the contact of the film and the strength of the same, it is preferable to add, to the fluorine compound serving as the raw material, oxygen, hydrogen, helium, argon, nitrogen, silane, hydrocarbon or the like. The plasma can effectively be generated by a DC or RF glow discharge method, a microwave discharge method or a laser beam irradiation method. The fluororesin having the ether bond may be sputtered to cover the surface of the positive pole.

It is preferable that the thickness of the film to be formed on the surface of lithium ranges from 1nm (10 Å) to 100 µ, more preferably ranges from 5nm (50 Å) to 10 µ. The optimum thickness of the film differs depending upon the density or the void ratio of the film and considerably differs depending upon the type of the electrolytic solution. The thickness of the film can be adjusted by changing the concentration of the main material in the coating liquid for forming the film. If the plasma polymerization or sputtering is performed, the thickness can be adjusted by controlling the deposition time period.

Silicon Resin

The organic silicon compound may be any one of a material selected from a group consisting of alkoxysilane, alkylsilane, halogenated silane, siloxane, silane containing vinyl group, amino group, epoxy group, methacrylic group or mercaptal group introduced thereto, hydrogen - denatured, vinyl - denatured, hydroxyl group denatured, amino - denatured, carboxylic group denatured, chloro - denatured, epoxy denatured, methacryloxy - denatured, mercapto - denatured, fluorine - denatured, long-chain-alkyl denatured or phenyl - denatured polysiloxane, alkylene oxide denatured siloxane copolymer, silicon - denatured copolymer, alkoxysilane - denatured polymer, silicon - denatured urethane or silicon - denatured nylon.

If the organic compound is liquid, the film can be formed by a direct coating method or the organic compound is diluted in a solvent and then applied. If the organic compound is solid, a solution dissolved in a solvent may be applied. The application method may be a dipping method, a screen printing method, a spraying method, a roll coating method or the like. The viscosity of the coating solution must adequately be adjusted to be adaptable to the coating method.

Titanium Polymer

A titanium polymer obtained by causing an organic titanium compound to act on an organic polymer may be used. For example, a thiranopolymer of silicon polymer formed by cross linking the main chain of a polycarbosilane skeleton with the titanium organic compound may be used.

As an alternative to the titanium polymer, a material obtained by introducing the derivative of an organic metal compound, such as an organic aluminum compound, into a polymer by substitution reactions may be used as the coating material.

Polyphosphazene

Polyphosphazene which is a polymer in which phosphor atoms and nitrogen atoms alternately form phosphor-nitrogen double bonds can be obtained by heating a dichloropolyphosphazene trimer to 200 to 300°C and by ring-opening polymerization. The dichloropolyphosphazene trimer can be synthesized from phosphorus pentachloride and ammonia chloride or ammonia. Any one of the following catalyzer is used at the time of the polymerization: benzoic acid, sodium benzonate, 2, 6 - di - p - cresol, water, methanol, ethanol, nitromethane, ether, heteropoly acid, sulfur, zinc, tin and sodium.

Further, various type of polyorganophosphazene can be obtained by substituting chloride atoms of polydichlorophosphazene by an organic reagent or an organic metal reagent.

If the surface of positive pole is coated with the foregoing polyphosphazene, it is preferable that the polymer solution dehydrated and deoxidized sufficiently be used in inactive gas dehydrated sufficiently. It is preferable to use a solvent in the foregoing solution which has been dehydrated with active alumina, molecular sieve, phosphorus pentaoxide or calcium chloride. As an alternative to this, it is preferable depending upon the type of the solvent that the solvent be distilled under presence of alkali metal in inactive gas to remove impurities and to be dehydrated.

An electrolyte may previously be mixed when the foregoing film is formed. It leads to a fact that wettability between the electrolytic solution and the film can be improved, causing ions to easily pass through the film.

Since the performance of the battery deteriorates if the polymer coating film is dissolved in an organic solvent of the electrolyte, it is preferable to be crosslinked in such a manner, for example, ultraviolet rays, electron rays or radial rays are applied or a crosslinking material, such as a radical generating agent, is used.

It is preferable that the thickness of the film to be formed on the surface of lithium ranges from 1nm (10 Å) to 100 µ, more preferably ranges from 5nm (50 Å) to 10 µ. The optimum thickness of the film differs depending upon the density or the void ratio of the film and considerably differs depending upon the type of the electrolytic solution. The thickness of the film can be adjusted by changing the concentration of the main material in the coating liquid for forming the film.

Polyolefin

As polyolefin, polyethylene or polypropylene may be used. Polyolefin is used in such a manner that the positive pole is dipped in a solution dissolved in a solvent such as tetrahydrofuran or o-dichlorobenzene, the positive pole is then dried and crosslinked by ultraviolet, electrons, radial rays or the like so that the film is formed on the surface of the positive pole.

The film can be formed by sputtering or plasma CVD method. In the material in the plasma CVD method, ethylene gas or propylene gas may be used.

Inorganic Oxide

The inorganic glass is made of a material, such as silica, titanium oxide, alumina, zirconia oxide, magnesium oxide, tantalum oxide, molybdenum oxide, tungsten molybdenum, tin oxide, indium oxide, iron oxide, chrome oxide, aluminum phosphate, iron phosphate, silicon phosphate and their mixtures. A sol-gel method is one of adequate methods for forming the inorganic glass. The raw material for the material having the inorganic glass structure is obtained in such a manner that an acid or a base and water are added to a solution of alcohol of an organic metal compound such as a metal alkoxide to hydrolyze the raw material so as to form colloid particles having metal atom-oxygen atom bonds, and then the colloid solution is directly applied to the surface of the positive pole. As an alternative to this, a solution in which a monomer or an organic polymer or the organic polymer and a crosslinking material are dissolved in the colloid solution is applied, and then the solution is polymerized or dried and polymerized so that the film is formed. By forming the composite organic polymer, strength against cracks and separation can be improved. If the electrolyte forming the lithium battery is dissolved in the colloid solution to form the film, the wettability with the electrolytic solution can be improved and ions are enabled to move easily.

As an alternative to alkoxide, any one of the following organic metal compound may be employed: acetyl acetone complex salt, an alkyl metal compound, acetyl acetone metal salt, naphthene acid metal salt, and octyl acid metal salt.

The organic polymer for combining the organic polymers is exemplified by epoxy resin, polyester, polyimide, polyethylene, polypropylene, polyurethane, polystyrene, polyethylene glycol, nylon, fluorine resin and silicon resin.

The polymer crosslinking material is exemplified by diisocyanate, polyisocyanate prepolymer, block isocyanate, organic peroxide, polyamine, oxims, nitroso compound, sulfur or sulfur compound, selenium, magnesium oxide, lead oxide and zinc oxide.

As an alternative to using the crosslinking material, a method may be employed in which radial rays or electron rays or ultraviolet rays are applied to polymerize or crosslink the polymer.

As an application method, a dipping method, screen printing, spraying or a roll coating method may be employed. The viscosity of the liquid to be applied must adequately be adjusted to be adaptable to the application method.

Another method of forming the film by the glass inorganic oxide may be employed, for example, any one of the following evaporation method or a CVD method may be employed: a sputtering method, an electron beam evaporation method, a plasma CVD (Chemical Vapor Deposition) method, and a laser CVD method.

The sputtering process and the electron beam evaporation can be performed by a method in which the oxide material is directly evaporated or by a method in which silicon or metal vapor and oxygen gas are caused to react with each other to form the film.

The plasma CVD method and the laser CVD method is performed in such a manner that oxygen gas and any one of a hydroxide or halide of silicon or metal and an organic metal compound are used as the raw materials to be decomposed by discharge or laser so that the film is formed.

The inorganic oxide can be used to form the film by another method, that is, an electrochemical method comprising the steps of forming a metal film made of aluminum, titanium, tantalum, niobium by sputtering or electron beam, anode-oxidizing the film by using an oxalic acid, a phosphoric acid or ammonia borate as an electrolytic solution to form the oxide film.

A film forming method may be employed which utilizes the equilibrium reaction in the water solution to precipitate and cause the oxide film to grow on the surface of the dipped substrate. In this case, silica (a silicon oxide), titanium oxide or vanadium oxide film can be formed. A specific method of forming the silica film comprises the step of dipping the positive pole in a solution in which silica is saturated in a water solution of hydrofluosilisic acid to form the film.

Nitride

The nitride can be obtained from silicon nitride, titanium nitride, aluminum nitride or boron nitride or the like. The nitride film can be formed on the positive pole by-sputtering, an electron beam evaporation method, a plasma CVD method or a laser CVD method.

The sputtering and the electron beam evaporation methods are categorized to a method in which the nitride material is directly evaporated and a method in which vapor of silicon, titanium or aluminum and nitrogen plasma generated from nitrogen gas or ammonia gas are caused to react with each other to form the film.

The plasma CVD method and the laser CVD method respectively comprise the step of decomposing the raw material gas, such as nitrogen gas, ammonia gas or nitrogen trifluoride and a hydroxide such as silicon, titanium or aluminum, halide or an organic metal compound by discharge or laser to form the film.

Carbide

The carbide can be obtained from a material exemplified by amorphous carbon, silicon carbide, titanium carbide, vanadium carbide and tungsten carbide.

The carbide film can be formed by a similar method employed to form the nitride.

The sputtering and the electron beam evaporation methods are categorized to a method in which the material from which the carbide is obtained is directly evaporated and a method in which silicon, titanium, vanadium or tungsten and carbon are used as the raw materials to form the film.

The plasma CVD method and the laser CVD method respectively comprise the step of, by laser, decomposing the material, such as hydrocarbon, from which carbon is obtained and a hydroxide such as silicon, titanium, vanadium or tungsten or a halide or an organic metal compound to form the film.

Halide

The halide can be obtained from a material selected from a group consisting of lithium fluoride, magnesium fluoride, sodium fluoride, potassium fluoride, barium fluoride or lithium chloride.

The halide film can be formed by a sputtering method or an electron beam evaporation method. A CVD method such as the plasma CVD method or the laser CVD method may be employed.

Semiconductor

The semiconductor for covering the positive pole is made of a material exemplified by diamond (carbon), silicon, nickel oxide, copper oxide, vanadium oxide, tin oxide and zinc oxide.

Alkali metal, phosphorus or boron may be added as impurities.

The semiconductor film may be formed by sputtering, electron beam evaporation, plasma CVD or laser CVD as well as the foregoing method of forming the inorganic acid film.

Thickness of Film Covering the Surface of Positive Pole

The thickness of the film for covering the surface of the positive pole can be controlled by adjusting the concentration of the solution if the surface is covered by utilizing the liquid layer reactions performed by the polymer solution or the sol-gel method. The same can be controlled by adjusting the deposition time if sputtering, the electron beam evaporation, the CVD method or the plasma polymerization is employed.

Aperture in Coating Film on Positive Pole Surface

The apertures and the void ratio of the coating film for covering the surface of the positive pole can be controlled by adjusting the concentration of the solution or the drying condition if covering is performed by using the polymer solution or by utilizing the sol-gel method. Further, any one of the following methods may be employed: a method for forming the film while causing foam to be generated by adjusting the concentration of the foaming material; a method having the steps of forming a film in which the content of the electrolyte is adjusted, and dissolving the electrolyte; a method for controlling the evaporation rate; and a method for adjusting the mixture ratio of the reactive materials.

If the negative pole is covered with the coating material of a type employed to cover the positive pole, growth of dendrite from the negative pole can be prevented. Therefore, short circuits in the battery can be prevented in effect obtainable from covering the positive pole. As a result, the battery cycle can further be lengthened.

Then, a positive pole according to the present invention composed of transition metal and oxygen will now be described.

Transition Metal Element

The transition metal element in the positive pole activating material according to the present invention may be an element having partially shell d or shell f and selected from a group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Wn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag and Au. Any one of the first transition system metal is mainly used which is exemplified by Ti, V, Cr, Mn, Fe, Co, Ni or Cu. A compound of the transition metal and the group 6A element is manufactured by a material exemplified by the transition metal, the salt of the transition metal, an oxide of the transition metal and a hydroxide of the transition metal.

Additive Element

By adding elements except the transition metal, the distortion of the positive pole activating material occurring due to the introduction/discharge of lithium ions can be relaxed. The element can be effectively added by a method comprising the step of adding the salt, the halide or an organic metal compound of one or more types of elements selected from a group consisting of lithium, magnesium, sodium, potassium, aluminum, zinc, calcium, barium, lead, indium, boron, silicon, tin, phosphor, arsenic, antimony, bismuth, chlorine and fluorine. It is preferable that the atom ratio of the additive element with respect to the transition metal element be 1 or less.

Method of Manufacturing Compound of Transition Metal and Oxygen

The compound of the transition metal and oxygen according to the present invention is manufactured by any one of methods categorized to a method in which the compound is prepared from the solution of the salt of the transition metal or the organic transition metal compound by way of a hydroxide, a method comprising the steps of melting the transition metal or the transition metal compound and rapidly cooling it, and a method in which the transition metal compound is caused to react in a gas phase.

The method of preparing the transition metal oxide from the hydroxide is exemplified by a method comprising the step of baking or drying hydroxide in air or in an oxygen atmosphere to prepare powder.

The rapid cooling method for preparing the transition metal oxide comprises the steps of melting the transition metal compound, such as the transition metal or the transition metal oxide, and spraying oxygen gas containing inactive gas mixed thereto to a rotating disc to prepare the powder.

The method of preparing the transition metal oxide by the gas phase reactions comprises the step of oxidizing or hydrolyzing the salt of the transition metal or causing vapor of the transition metal to react with oxygen or a compound of oxygen or decomposing the organic transition metal compound to prepare the powder.

It is preferable that each process be performed at 400°C or lower, more preferable 300°C or lower.

The liquid phase reaction method, the gas phase reaction method and the melting and rapid cooling method will now be described.

Liquid Phase Reaction

A method of preparing the hydroxide for use in the main reaction in the method of manufacturing the material from the solution by way of the hydroxide is exemplified by:

Method of Preparing Hydroxide

It is preferable that the transition metal hydroxide be prepared by reactions between the salt of the transition metal and alkali or by hydrolysis of the organic transition metal compound or by reactions between the transition metal and alkali. It is preferable that the preparation temperature be 150°C or lower, more preferably 100°C or lower.

Reactions between Salt of Transition Metal and Alkali

By causing alkali to react with the salt of the transition metal, a hydroxide of the transition metal is sedimentated to be prepared. By mixing salts of two or more types of the transition metals, a hydroxide of a composite transition metal can be obtained.

The salt of the transition metal is typified by a carbonate, a nitrate, a halide, a sulfate, a sulfamate, acetate, oxalate, citrate, tartrate, formate or ammonate.

The alkali may be lithium hydroxide, sodium hydroxide, potassium hydroxide or ammonia hydroxide. As an alternative to this, urea or thiourea may be used which raises the pH by generating hydroxide ions when heated.

It is preferable that an organic acid or inorganic acid or an amine is, in a small quantity, added or an organic solvent such as alcohol is added at the time of causing alkali to react with the water solution of the transition metal salt in order to fine the sediment particles of the hydroxide.

By vibrating the sediment with ultrasonic waves, the sediment particles can be fined. Therefore, the specific area can be enlarged.

Hydrolysis Reaction of Organic Transition Metal Compound

The hydroxide of the transition metal can be prepared by hydrolyzing an organic metal compound of the transition metal, such as alkoxide, acetyl acetenate, octylate or naphthalate.

The hydrolysis of alkoxide is specifically performed in such a manner that alkoxide of the transition metal is dissolved by water, alcohol or ethanol amine or the like, and an inorganic acid such as hydrochloric acid or an organic acid such as acetic acid or ammonia hydroxide or amine is added.

The alkoxide of the transition metal may be a material selected from a group consisting of Mn(OC₂H₅)₂, Mn(OC₃H₇)₂, Mn(OC₄H₉)₂, Ni(OC₂H₅), Ni(OC₃H₇)₂, Ni(OC₄H₉)₂, Co(OC₂H₅)₂, Co(OC₃H₇)2, Co(OC₄H₉)₂, Ti(OC₂H₅)₂, Ti(OC₃H₇)₂, Ti(OC₄H₉)₂, Fe(OC₂H₅)₂, Fe(OC₃H₇)₂, Fe(OC₄H₉)₂, Cu(OC₂H₅)₂, Cu(OC₃H₇)₂, Cu(OC₄H₉)₂, VO(OCH₃)₃, VO(OC₂H₅)₃, VO(OC₃H₇)₃, VO(OC₄H₉)₃ and Y(OC₄H₉)₃.

The acetylacetonate of the transition metal is exemplified by Cu(C₅H₇O₂)₂, Co(C₅H₇O₂)₂, (H₂O)₂, Co(C₅H₇O₂)₃, Ni(C₅H₇O₂)₂(H₂O)₂, Mn(C₅H₇O₂)₂(H₂O)₂, Cr(C₅H₇O₂)₃, VO(C₅H₇O₂)₂, Fe(C₅H₇O₂)₃, Ti(OC₄H₉)₂(C₅H₇O)₂, La(C₅H₇O₂)₃, Y(C₅H₇O₂)₃, and Zr(C₅H₇O₂)₄.

The octylate of the transition metal is exemplified by Cu(C₇H₁₅COO)₂, Ni(C₇H₁₅COO)₂, Fe(C₇H₁₅COO)₂, Mn(C₇H₁₅COO)₂, Co(C₇H₁₅COO)₂, Zr(C₇H₁₅COO)₂, Y(C₇H₁₅COO)₂, and La(C₇H₁₅COO)₂.

The naphthate of the transition metal is exemplified by the salt of naphthate expressed by a general formula C_nH_2n-2O₂, that is, cobalt naphthenate, copper naphthenate, manganese naphthenate, iron naphthenate, nickel naphthenate, vanadium naphthenate, yttrim naphthenate and lanthanum naphthenate.

The alcohol is exemplified by methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol and propylene glycol.

Dehydrating Reaction

In order to obtain the oxide of the transition metal by dehydration from the transition metal hydroxide prepared by the foregoing solution reactions, it is preferable that the transition metal hydroxide is immersed in an organic solvent such as alcohol or acetone which is mixed with ether to sufficiently substitute water, and then it is dried in a vacuum state at 100°C or higher. As an alternative to this, heating and dehydration is performed by using microwaves. If the drying temperature is too high, crystallization is enhanced and therefore the hydroxide groups are deceased. Therefore, it is preferable that the temperature be 400°C or lower. It is preferable that the frequency of the microwaves be a frequency which can easily be absorbed by water.

In order to enlarge the specific area, another method may be employed in which the dehydration is performed by freezing and drying.

Hydrogen Treatment

Hydrogen is mixed into the dried atmosphere at the time of drying the transition metal oxide followed by performing heat treatment. As an alternative to this, a method is employed in which the transition metal hydroxide or the transition metal oxide is subjected to hydrogen plasma treatment. The hydrogen plasma can be generated by a hydrogen gas discharge method or by a method of exciting and decomposing the hydrogen gas by laser beams.

Gas Phase Reaction Method

As a method of preparing a compound of the transition metal and oxygen, a gasified transition metal salt or an organic transition metal compound or vapor of the transition metal and oxygen or an oxygen compound are caused to react with each other in the gas phase to prepare powder. Another method may be employed in which the gasified transition metal salt or the organic transition metal compound containing oxygen is decomposed in the gas phase to prepare the compound of the transition metal and oxygen.

If the transition metal salt or the organic transition metal compound is in the form of solid, it is heated as to be formed into vapor or it is heated as to be formed into liquid. Then, carrier gas is bubbled as to be introduced into the reaction chamber. If the transition metal salt or the organic transition metal compound is in the form of liquid, it may be heated as to be formed into vapor or carrier gas is bubbled as to be introduced into the reaction chamber.

The salt of the transition metal may mainly be a halide such as a chloride. As an alternative to this, a carbonate, a nitrate, a sulfate, sulfominate, acetate, citrate, tartrate, formate or ammonate. The chloride is exemplified by VOCl₃, MnCl₂, MoCl₅, TiCl₄, NiCl₂, CoCl₂, FeCl₃, WCl₆, YCl₃ and ZrCl₄.

The raw material from which oxygen can be obtained is exemplified by oxygen, hydroxide and an oxyhalide.

By mixing hydrogen gas in the foregoing gas phase reaction, a compound of the transition metal and the group 6A element containing hydrogen can be prepared.

In the foregoing gas phase reaction, it is preferable to employ any one of the following methods: a heat CVD (Chemical Vapor Deposition) method, a plasma CVD method, a laser CVD method, a filament method, a reactive sputtering method and the electron beam method.

The reactions performed by heat in the heat CVD method, by glow discharge in the plasma CVD method, by heat energy or light energy of laser beams in the laser CVD method, by heat of a filament made of tungsten or the like in the filament method, and in the reactive sputtering method in the reactive gas atmosphere, and by electron beam heating in the electron beam method. As a result, gas phase reactions are respectively performed so that the material is prepared. It is preferable that the raw material be in the form of solid in the reactive sputtering method or the electron beam method.

Rapid Cooling Method

In this case, any one of the following methods may be employed: a gun method comprising the steps of generating, while breaking a Mylar film, shock waves by helium gas, in which oxygen or hydrogen sulfide is mixed, as to be sprayed to the transition metal or the transition metal compound melted with high frequency waves, and causing blown compound powder to impact against a cooling steel plate in the form of a slide disposed below so that the temperature is rapidly cooled; a method in which a molten bath is dispersed by spraying with inactive gas jet in which oxygen or hydrogen sulfide is mixed; and an atomization method in which molten bath of the transition metal or the transition metal compound is sprayed in an atmosphere containing oxygen or an oxygen compound as to be formed into powder. By mixing hydrogen gas into the inactive gas, hydrogen can be introduced into the product.

It is preferable that the rapid cooling rate be 10¹ to 10⁸ K per second, more preferable 10² to 10⁸ K per second.

The melting and heating furnace may be a crucible furnace, an induction furnace, an arc furnace or an electron beam furnace.

The method of causing the alkali to directly react with the transition metal is exemplified by a method in which metal such as vanadium is caused to react with molten alkali to prepare an oxide.

Conductor Core

When conductor powder is mixed at the time of preparing the compound of the transition metal and oxygen to cause the compound of the transition metal and oxygen to grow while using the conductor powder as the core, the collecting efficiency can be raised. Therefore, the introduction and discharge of lithium ions can be made easier, and therefore the battery capacity can be enlarged.

The conductor powder may be made of one or more types of materials selected from a group consisting of carbon, titanium, nickel, cobalt, iron, chrome, manganese, vanadium, platinum, palladium, copper, silver, gold, zinc, tin, indium, lead, tungsten and molybdenum. It is preferable to use one or more types of elements selected from a group consisting of carbon, titanium, nickel, cobalt, iron, chrome, manganese, vanadium and platinum.

The shape of the conductor powder is formed into one or more types of shapes selected from a group consisting of a spherical shape, a flake shape, a needle shape and a fiber shape. As a result, also the compound powder of the transition metal and oxygen can be formed into the spherical, flake, needle or fiber shape. Therefore, the efficiency of the electron movement between the positive pole activating material can be raised, and therefore the charging and discharging efficiency can be improved.

It is preferable that the diameter of the conductor powder be 1nm (10 Å) to 100 µ when measured by an electron microscope, more preferably 1nm (10 Å) to 10 µ.

Crushing of Positive Pole Activating Material

The prepared positive pole activating material must be crushed as to have an adequate grain size if obtained positive pole activating material is in the form of a block.

It is preferable to crush the positive pole activating material by using, while combining, means selected from a group consisting of a compression crushing machine, a shearing crushing machine, an impact crushing machine, a roll mill, a roller mill, a highspeed rotational mill, a ball mill, a medium stirring mill, a jet mill, a mortar and a stamping mill.

Coating Film Made of Conductor

The prepared compound of the transition metal and oxygen is covered with a conductor thin film by chemical plating (electroless plating) or by evaporation. As a result of the foregoing process, the current collecting efficiency can be raised, the intercalation/deintercalation of lithium ion can be facilitated and the battery capacity can be enlarged.

The conductor thin film may be made of one or more types of materials selected from a group consisting of carbon, titanium, nickel, cobalt, iron, chrome, manganese, vanadium, platinum, paradium, copper, silver, gold, zinc, tin, indium, lead, tungsten and molybdenum. It is preferable to use one or more types of elements selected from a group consisting of carbon, titanium, nickel, cobalt, iron, chrome, manganese, vanadium and platinum.

The chemical plating method is a method in which metal ions are deoxidized by a deoxidizer such as formaldehyde to precipitate the metal film.

The evaporation is performed by any one of the following methods: a method in which vapor of metal is generated by electron beams or laser beams as to be applied to the subject; a method in which a carbon or metal target is sputtered as to be applied to the subject; a method in which hydrocarbon or organic solvent or an organic metal compound is decomposed by discharge or laser or heat as to be applied to the subject. The decomposition of the hydrocarbon and the organic solvent enables a carbon film to be formed, while the decomposition of the organic metal compound enables a metal film to be formed.

It is preferable that the thickness of the conductor film ranges from 5nm (50 Å) to 1 µ.

Lipophilic Treatment

The positive pole activating material is subjected to the lipophilic treatment in such a manner that the organic metal compound is immersed in a solution, in which an organic solvent is dissolved, and then it is dried.

It is preferable that the organic metal compound for use in the lipophilic treatment be an organic metal compound such as silane coupling material or organic titanate. If dilution is performed, the dilution concentration with respect to the solvent ranges from 0.05 to 2 wt%.

The silane coupling material is exemplified by vinyltrimethoxysilane, vinylethoxysilane, N - (2 - aminoethyl) 3 - aminopropylmethyl dimethoxysilane, N - (2 - aminoethyl) 3 - aminopropyltrimethoxysilane, 3 - aminopropyltriethoxysilane, 3 - glycidexypropyltrimethoxysilane, 3 - glycidexypropylmethyldimethoxysilane, 2 - (3,4 - epoxycychlohexyl) ethyltrimethoxysilane, 3 - chloropropylmethyldimethoxysilane, 3 - chloropropyltrimethoxysilane, 3 - methacryloxytrimethoxysilane, 3 - mercaptotrimethoxysilane, and N - [2 - (vinylpenzilamino)ethyl] - 3 - aminopropyltrimethoxysilane.

The organic titanate is exemplified by tetra - i - propoxytitanium, tetra - n - butoxytitanium, tetrakis (2 - ethylhexyloxy)titanium, tetrastearyloxytitanium, di - i - proxy·bis (acetylacetate)titanium, dihydroxy·bis (lactato)titanium, titanium - i - propoxyoctylene glycol, titanium stearate, propane dioxytitanbis (ethylacetoacetate), propanedioxytitanium (acetylacetonate) (ethylacetoacetate), oxotitanbis (monoammonaium oxalate), tri - n - butoxytitanmonostearate, and titan polymer.

Analysis of Transition Metal and Oxygen Measurement of Size of Crystal Grain

The size of crystal grains was evaluated from the peak half width and the angle of diffraction of X-ray diffraction curve in accordance with the following Scherrer's Formula: <maths id="math0001" num="(Scherrer's Formula)"><math display="block"><mi mathvariant="normal">t</mi><mo>=</mo><mn>0.9</mn><mo>⁢</mo><mi mathvariant="normal">λ</mi><mo>/</mo><msub><mi mathvariant="normal">Bcosθ</mi><mi mathvariant="normal">B</mi></msub></math><img file="EP0809314B1_D0001.tif" /></maths> where t: size of crystal grain λ: wave length of X-ray beam B: peak half width θ_B: angle of diffraction

The size of the crystal grain of the positive pole activating material which is the compound of the transition metal and oxygen for use in the secondary battery according to the present invention is 50nm (500 Å) or less when calculated by using the foregoing Scherrer's Formula, more preferably 20nm (200 Å) or less.

Observation of Crystal Structure

The crystal structure of the positive pole activating material prepared by the method according to the present invention can be observed in such a manner that the waveform of the radial distribution function can be observed by X-ray diffraction, the diffraction pattern can be observed by reflecting high speed electron beam diffraction (RHEED) and the waveform of the X-ray diffraction curve can be observed.

The radial distribution function can be obtained by Fourier transforming the dispersion intensity of measured X-ray or neutron beam. The radial distribution function is expressed by the presence possibility of atoms with respect to an arbitrary atom or a function of the deviation distance from an average numerical density. If the specimen is made of amorphous material, a moderate peak curve can be obtained. If the specimen is crystal material, a discontinuous sharp peak can be obtained.

The RHEED enables a halo pattern to be observed if the specimen is made of amorphous material, enables a ring pattern to be observed if the specimen is made of microcrystal material and enables a spot pattern to be observed if the specimen is made of a multi-crystal material.

The dispersion angle and the dispersion intensity obtainable in the X-ray small angle dispersion method also enables of fluctuation of ununiform density peculiar to the amorphous material.

Further, the differential thermal analysis enables heat absorption or heat generation due to the structural relaxation or the crystallization structural change occurring to the temperature rise to be observed if the specimen is amorphous material. If a hydroxide group is present, heat absorption due to dehydration can be observed.

By using the foregoing means, the structure of the compound of the transition metal and oxygen prepared by the manufacturing method according to the present invention can be analyzed so that the amorphous structure, the microcrystal structure and the multi-crystal structure are confirmed.

Analysis of Hydrogen

The compound of the transition metal containing hydrogen and oxygen is subjected to qualitatively analyzed by SIMS (Secondary Ion Mass Spectrometry) analysis.

Manufacturing of Positive Electrode

The positive electrode is manufactured in such a manner that the bonding material, and conductive powder if necessary, is mixed with the powder of the compound of the transition metal and oxygen manufactured by the foregoing method, and then formed into the positive electrode together with the collector. It is preferable that the forgoing forming process be performed in dry air from which water has sufficiently been removed, more particularly under inactive gas atmosphere.

The conductive powder acts to enhance the electron conduction and facilitate the current collection because the active material, which is the compound of the transition metal and oxygen, does not substantially have the electron conductivity.

The conductive powder may be carbon material, such as acetylene black, ketchen black or graphite powder, or metal, such as nickel, titanium, copper or stainless steel. It is preferable that the mixture ratio of the conductive powder with respect to the positive pole active material be 1 or less.

The bonding material bonds the positive pole active material powder to one another and prevents generation of cracks in the charge and discharge cycle to prevent the separation from the collector. The bonding material may be one or more types of resin which are stable against the organic solvent and which are selected from a group consisting of fluororesin, polyethylene, polypropylene and silicon resin. It is preferable that the foregoing resin be in the form of liquid or solution or having a low melting point. Further, it is preferable that the solvent be removed and the resin is crosslinked during the process of manufacturing the positive pole. As a result, the content of the bonding material in the positive pole can be lowered and the capacity of the battery can be improved. The liquid resin or the resin which can be dissolved in the solvent is exemplified by fluororesin having an ether bond and silicon resin. If the fluororesin having the ether bond is used, the concentration can be lowered when it is dissolved in a solvent. Therefore, the content in the positive pole can be lowered as much as possible and the void ratio can be raised. Further, the state is very stable after crosslinking has been performed so that a satisfactory effect can be obtained upon the charge and discharge cycle.

It is also preferable that dehydration is performed with heat generated by microwaves and a vacuum drier is used to dehydrate the positive pole after the positive pole has been formed.

It is preferable that the mixture ratio of the bonding material with respect to the positive active material be 0.1 or less.

Examples

Examples of the present invention will now be described. It should be noted that the present invention is not limited to the examples below.

Preparation of Positive Pole Activating Material

Methods of preparing the positive pole activating material according to the present invention are exemplified in Preparation Methods 46-51 and 53-55 and the conventional preparation methods are exemplified by Comparative Preparation Methods.

Preparation Method 46

A lithium-manganese oxide was prepared as follows.

Manganese acetate was dissolved in water, and then super fine nickel powder ENP-005 manufactured by Sumitomo Denko was suspended in a water solution of manganese nitrate. Then, a water solution of lithium hydroxide was dripped until the pH was 8 or higher while vibrating the suspension solution with supersonic vibrations of 20 kHz so that sedimentation was generated. Then, ethyl alcohol was added, and supernatant liquid of the solution including the sediment was removed by decantation. The ethylalcohol cleaning and the decantation were repeated. Then, it was dissolved in 0.1% methyl alcohol solution of Sila Ace S210 (vinylmethoxysilane) which was a silane coupling material manufactured by Chisso. Then, the solvent was removed by a centrifugal separator. The obtained sedimentation was dried at 120°C, and dried at 200°C in a vacuum drier so that grains of manganese oxide were prepared.

The size of crystal grains was measured from the half value width of the X-ray analysis curve with respect to a manganese oxide and the angle of diffraction in accordance with the Scherrer's Equation. The size of the crystal grain was 6nm (60 Å) or larger.

The RHEED pattern resulted in a ring pattern like a halo pattern.

The X-ray radial distribution function resulted in a continuous and moderate peak curve.

The scattering angle and the scattering intensity obtainable from the X-ray small angle scattering method resulted in non-uniform density fluctuation to be observed.

The specific area was measured by the BET method, resulting in that the specific area was 123 m²/g.

Preparation Method 47

Vanadium oxide was prepared as follows.

Vanadium pentaoxide was gradually added to a water solution of lithium hydroxide as to be dissolved. While applying supersonic vibrations, the water solution was sprayed into liquid nitrogen as to be frozen. Then, the temperature was raised to -20°C, and the pressure was lowered so that freezing and drying were performed to dehydrate and dry the material. Obtained grains were dried at 150°C, and further dried in a vacuum drier at 250°C so that grains of vanadium oxide were obtained. Then, the sample was immersed in 0.1 % isopropylalcohol solution of tetra-iso-propoxytitanium, and then the solvent was removed by a centrifugal separator. The obtained sedimentation was dried at 120°C, and then dried at 200°C in a vacuum state so that grains of manganese oxide were prepared.

Although the size of crystal grains was intended to measure from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation, it could not be measured because the diffraction curve resulted in a broad form.

The RHEED pattern resulted in a halo pattern.

The X-ray radial distribution function resulted in a continuous and moderate peak curve.

The scattering angle and the scattering intensity obtainable from the X-ray small angle scattering method resulted in non-uniform density fluctuation to be observed.

The specific area was measured by the BET method, resulting in that the specific area was 105 m²/g.

Preparation Method 48

A lithium-nickel oxide was prepared as follows.

Nickel acetate was dissolved in a mixture solvent of acetic acid, ethyl alcohol and water. While vibrating the solution with supersonic vibrations of 20 kHz, an ethyl alcohol solution of ethoxylithium, which was alkoxide, was dripped as to be mixed. Then, the solution was heated to 80°C to enhance the hydrolysis decomposition reactions so that sol was generated. The supernatant liquid of the solution including the sol-shape sedimentation was removed by decantation, cleaned with ethyl alcohol, the decantation was repeated and the solvent was removed by a centrifugal separator. The obtained sedimentation was dried at 150°C, and then suspended in a non-electrolyzed nickel plating solution Ni-701 manufactured by Kojundo Kagaku. Then, it was heated to 70°C, nickel coating was performed, and water cleaning and decantation were repeated. Then, ethyl alcohol cleaning was performed, and decantation was repeated, and then the solvent was removed by a centrifugal separator. The sample was dried at 230°C in a vacuum state so that grains of nickel oxide were obtained.

Although the size of crystal grains was intended to measure from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation, it could not be measured because the diffraction curve with respect to an oxide resulted in a broad form.

The RHEED pattern resulted in a ring pattern considered due to nickel plating. The pattern before the nickel plating process resulted in a halo pattern.

The X-ray radial distribution function resulted in a continuous and moderate peak curve. The scattering angle and the scattering intensity obtainnable from the X-ray small angle scattering method resulted in non-uniform density fluctuation to be observed.

The specific area was measured by the BET method, resulting in that the specific area was 210 m²/g.

Preparation Method 49

A lithium-nickel-cobalt oxide was prepared by the following method.

Nickel nitrate and cobalt nitrate were dissolved in water, and then a water solution of lithium hydroxide was dripped to a solution of the nickel nitrate and cobalt nitrate while vibrating with supersonic vibrations of 20 kHz until the pH was 8 or higher so that sedimentation was generated. Then, ethyl alcohol was added so that the supernatant liquid of the solution including the sedimentation was removed by decantation. The ethyl alcohol cleaning and the decantation were repeated and the solvent was removed by a centrifugal separator. The obtained sedimentation was dryed at 120°C, dried at 200°C in a vacuum state so that grains of a nickel cobalt oxide were prepared.

The size of crystal grains was measured from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation. The size of the crystal grain was 14nm (140 Å).

The RHEED pattern resulted in a ring pattern like a halo pattern.

The X-ray radial distribution function resulted in a continuous and moderate peak curve.

The scattering angle and the scattering intensity obtainable from the X-ray small angle scattering method resulted in non-uniform density fluctuation to be observed.

The specific area was measured by the BET method, resulting in that the specific area was 160 m²/g.

Preparation Method 50

Vanadium-molybdenum oxide was prepared as follows.

Vanadyl sulfate and molybdenum sulfate were added to water as to be suspended, and acetic acid was gradually added as to be dissolved. Then, a water solution of lithium hydroxide was dripped to a solution of the vanadium oxide and acetic acid while vibrating with supersonic vibrations of 20 kHz until the pH was 8 or higher so that sedimentation was generated. Then, ethyl alcohol was added so that the supernatant liquid of the solution including the sedimentation was removed by decantation. The ethyl alcohol cleaning and the decantation were repeated and the solvent was removed by a centrifugal separator. The obtained sedimentation was dryed at 120°C, dried at 200°C in a vacuum state so that grains of a vanadium oxide were prepared.

The size of crystal grains was measured from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation. The size of the crystal grain was 8nm (80 Å).

The RHEED pattern resulted in a ring pattern like a halo pattern.

The X-ray radial distribution function resulted in a continuous and moderate peak curve.

The scattering angle and the scattering intensity obtainable from the X-ray small angle scattering method resulted in non-uniform density fluctuation to be observed.

The specific area was measured by the BET method, resulting in that the specific area was 100 m²/g.

Preparation Method 51

Vanadium-molybdenum oxide was prepared by the following method.

The vanadium oxide and the molybdenum oxide were mixed at a ratio of 7:3, and heated up to 800°C as to be melted and mixed so that a molten bath was made. Then, the molten bath was dispersed by jet gas which was a mixture of 20% oxygen and 2% hydrogen with argon gas. It was sprayed at high speed to a cooled and retaining metal disc so that grains of vanadium oxide and molybdenum oxide were prepared.

The size of crystal grains was measured from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation. The size of the crystal grain was 11nm (110 Å).

The RHEED pattern resulted in a ring pattern having weak intensity.

The X-ray radial distribution function resulted in a continuous and moderate peak curve.

The scattering angle and the scattering intensity obtainable from the X-ray small angle scattering method resulted in non-uniform density fluctuation to be observed.

The specific area was measured by the BET method, resulting in that the specific area was 60 m²/g.

Preparation Method 52

Titanium sulfide was prepared by the following method.

Hydrogen gas was allowed to flow by 500 sccm into a reaction chamber of a plasma CVD apparatus degasified as to be vacuum state. The pressure was maintained at 1.3kPa (10 Torr) and discharge was caused to take place at a high frequency wave of 13.56 MHz. Then, 200 sccm of helium gas was, as a carrier gas, bubbled in a hexane solution of tetrabutoxytitanium, and injected by 200 sccm through a nozzle into the reaction chamber of the plasma CVD apparatus. Simultaneously, 250 sccm of hydrogen sulfide was introduced as to be reacted in a gas phase to capture grains of titanium sulfide by a capturing machine.

The size of crystal grains was measured from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation. The size of the crystal grain was 20nm (200 Å).

The RHEED pattern resulted in a ring pattern having weak intensity.

The X-ray radial distribution function resulted in a continuous and moderate peak curve.

The scattering angle and the scattering intensity obtainable from the X-ray small angle scattering method resulted in non-uniform density fluctuation to be observed.

The specific area was measured by the BET method, resulting in that the specific area was 175 m²/g.

Preparation Method 53

Lithium-iron-cobalt oxide was prepared by the following method.

A mixture solution of 0.5 mol/l cobalt chloride and 1 mol ferric chloride mixed at a ratio of 1:1 was gradually added to a 5 mol/l water solution of lithium hydroxide while stirring and bubbling argon gas. Then, reaction chamber was set to 100°C to be matured. After the maturation, it was injected into cooled water, and cleaning was performed with water cooled by water by means of decantation until the pH of the solution was 8. It was dried at 200°C in a vacuum state, and crushed by a ball mill in an atmosphere of argon gas.

The size of crystal grains was measured from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation. The size of the crystal grain was 15nm (150 Å).

The RHEED pattern resulted in a ring pattern having weak intensity to be observed.

The X-ray radial distribution function resulted in a continuous and moderate peak curve.

The scattering angle and the scattering intensity obtainable from the X-ray small angle scattering method resulted in non-uniform density fluctuation to be observed.

The specific area was measured by the BET method, resulting in that the specific area was 2100 m²/g.

Example 54

Manganese Acetate, magnesium chloride and urea were added to a solution in which 300 g of vanadium pentoxide was dissolved in 2 liters of hydrochloric acid, followed by heating the solution to 95 to 95°C for 10 minutes to generate ammonia. Lithium hydride solution was dripped to make the pH to generate sediment. Then, decantation and water cleaning were repeated, and then cleaning with ethyl alcohol was performed, and the material was dried by a spray drier. Then, the sample was dried at 200°C in a vacuum state.

The size of crystal grains was measured from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation. The size of the crystal grain was 9nm (90 Å).

The RHEED pattern resulted in a ring pattern like a halo pattern.

The X-ray radial distribution function resulted in a continuous and moderate peak curve.

The scattering angle and the scattering intensity obtainable from the X-ray small angle scattering method resulted in non-uniform density fluctuation to be observed.

The specific area was measured by the BET method, resulting in that the specific area was 80 m²/g_.

Preparation Method 55

A lithium-copper-cobalt oxide was prepared by the following method.

An oxalic acid was added to a water solution in which a copper sulfate and a cobalt nitrate were dissolved. Then, supersonic vibrations were applied, and lithium hydroxide was dripped until the pH was 7 so that sedimentation was generated. Water cleaning and decantation were repeated, and then, a water solution of lithium hydroxide was added, supersonic vibrations were applied, and an ethyl alcohol was added. Decantation and cleaning with ethyl alcohol were repeated, and the material was dried by using a spray drier. Further, the material was dried at 200°C in a vacuum state.

The size of crystal grains was measured from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation. The size of the crystal grain was 16nm (160 Å).

The RHEED pattern resulted in a ring pattern having weak intensity.

The X-ray radial distribution function resulted a continuous and moderate peak curve.

The scattering angle and the scattering intensity obtainable from the X-ray small angle scattering method resulted in non-uniform density fluctuation to be observed.

The specific area was measured by the BET method, resulting in that the specific area was 50 m²/g.

Other Analyses

The SIMS analysis resulted that the positive pole activating materials according to Preparation Methods 46 to 55 contained hydrogen and lithium. Also the dehydration peak of each TG (Thermogravimetric analysis), DTA (Differential Thermal Analysis) and DSC (Differential Scan Thermal Heating Value Measurement) and the absorption spectrum of FTIR (Fourier Transform Infrared) resulted that a hydroxyl group was present.

Comparative Preparation Method 46

A lithium-manganese oxide was prepared by the following method.

Powder of electrolyzed manganese dioxide manufactured by Mitsui Kinzoku and lithium carbonate were mixed with each other at a ratio of 1:0.4 and they were heated at 800°C so that lithium manganese oxide was prepared.

The size of crystal grains was measured from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation. The size of the crystal grain was 60nm (600 Å) or larger.

The RHEED pattern resulted in a ring pattern in which a spot pattern could be confirmed.

The X-ray radial distribution function resulted in discontinuous peak curve.

The specific area was measured by the BET method, resulting in that the specific area was 40 m²/g.

Comparative preparation Method 47

A reagent manufactured by Wako was dried at 400°C in a vacuum state.

The size of crystal grains was measured from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation. The size of the crystal grain was 80nm (800 Å).

The RHEED pattern resulted in a ring pattern in which a spot pattern could be confirmed.

The X-ray radial distribution function resulted in discontinuous peak curve.

The specific area was measured by the BET method, resulting in that the specific area was 4 m²/g.

Comaprative Preparation Method 48

A lithium-nickel oxide was prepared by the following method.

A lithium carbonate and nickel nitrate were mixed at an equal mol ratio of 1:1 and the mixture was heated to 800°C so that a lithium-nickel oxide was prepared.

The size of crystal grains was measured from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation. The size of the crystal grain was 200nm (2000 Å) or larger.

The RHEED pattern resulted in a ring pattern in which a spot pattern could be confirmed.

The X-ray radial distribution function resulted in discontinuous peak curve.

The specific area was measured by the BET method, resulting in that the specific area was 50 m²/g.

Comparative Preparation Method 49

A lithium-nickel-cobalt oxide was prepared by the following method.

A lithium carbonate, nickel carbonate and cobalt carbonate were mixed at a mol ratio of 10:3:7 and the mixture was heated to 900°C for 20 hours as to be decomposed so that a nickel-cobalt oxide was prepared.

The size of crystal grains was measured from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation. The size of the crystal grain was 110nm (1100 Å) or larger.

The RHEED pattern resulted in a ring pattern in which a spot pattern could be confirmed.

The X-ray radial distribution function resulted in discontinuous peak curve.

The specific area was measured by the BET method, resulting in that the specific area was 40 m²/g.

Comparative Preparation Method 50

A vanadium-molybdenum oxide was prepared by the following method.

A vanadium oxide and a molybdenum oxide were mixed at a ratio of 7:3, and the mixture was heated to 800°C in a platinum crucible as to be melted and mixed. Then, the mixture was cooled gradually so that the block-shape vanadium oxide and molybdenum oxide were prepared. They were crushed by a roller mill so that grains of vanadium oxide-molybdenum oxide were prepared.

The size of crystal grains was measured from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation. The size of the crystal grain was 70nm (700 Å) or larger.

The RHEED pattern resulted in a ring pattern in which a spot pattern could be confirmed.

The X-ray radial distribution function resulted in discontinuous peak curve.

The specific area was measured by the BET method, resulting in that the specific area was 10 m²/g.

Comparative Preparaton method 51

A titanium sulfide was prepared by the following method.

A titanium disulfide powder manufactured by Kojundo Kagaku was dried at 400°C in a vacuum state.

The size of crystal grains was measured from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation. The size of the crystal grain was 90nm (900 Å) or larger.

The RHEED pattern resulted in a ring pattern in which a spot pattern could be confirmed.

The X-ray radial distribution function resulted in discontinuous peak curve.

The specific area was measured by the BET method, resulting in that the specific area was 50 m²/g.

Comparative Preparation method 52

A lithium-iron-cobalt oxide was prepared by the following method.

Lithium carbonate, iron acetate and cobalt carbonate were mixed at the same mole ratio, and decomposed at 600°C in air so that an iron cobalt oxide was prepared. Then, it was crushed by a ball mill so that grains were obtained.

The size of crystal grains was measured from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation. The size of the crystal grain was 100nm (1000 Å) or larger.

The RHEED pattern resulted in a ring pattern in which a spot pattern could be confirmed.

The X-ray radial distribution function resulted in discontinuous peak curve.

The specific area was measured by the BET method, resulting in that the specific area was 40 m²/g.

Comparative Preparation Method 53

A manganese containing magnesium added thereto-vanadium oxide was prepared by the following method.

A manganese dioxide, vanadium pentaoxide and magnesium hydroxide were mixed at a mol ratio of 10:10: 1, and then they were decomposed at 700°C in air. As a result, the manganese containing magnesium added thereto-vanadium oxide was prepared. Then, they were crushed by a ball mill so that grains were obtained.

The size of crystal grains was measured from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation. The size of the crystal grain was 130nm (1300 Å) or larger.

The RHEED pattern resulted in a ring pattern in which a spot pattern could be confirmed.

The X-ray radial distribution function resulted in discontinuous peak curve.

The specific area was measured by the BET method, resulting in that the specific area was 27 m²/g.

Comparative Preparation Method 54

A lithium-copper-cobalt oxide was prepared by the following method.

A lithium carbonate, cobalt carbonate and copper carbonate were mixed at the same mol ratio, and then they were decomposed at 600°C in air. As a result, the manganese containing magnesium added thereto-vanadium oxide was prepared. Then, they were crushed by a ball mill so that grains were obtained.

The size of crystal grains was measured from the half value width of the X-ray analysis curve and the angle of diffraction in accordance with the Scherrer's Equation. The size of the crystal grain was 110nm (1100 Å) or larger.

The RHEED pattern resulted in a ring pattern in which a pot pattern could be confirmed.

The X-ray radial distribution function resulted in discontinuous peak curve.

The specific area was measured by the BET method, resulting in that the specific area was 10 m²/g.

Analyzing Apparatus

The positive electrode active material prepared by Preparation Methods 46 to 55 and Comparative Preparation Methods 46 to 54 were analyzed by using the following apparatuses. The X-ray diffraction measurement was performed by using MXP3VA manufactured by MacScience.

The RHEED measurement was performed by using JEM-100SX manufactured by Nihon Denshi.

The specific area measurement by the BET method was performed by using GEMIN12300 manufactured by Micromeritex.

As a result of the comparisons the compounds according to the present invention exhibited smaller particle grain size as compared with the results of Comparative Preparation Method while having an amorphous or microcrystal structure.

Manufacturing of Lithium Secondary Battery

Lithium secondary batteries were manufactured by using the positive electrode active materials prepared by the foregoing preparation methods.

Example 46

The positive electrode active material prepared by the foregoing Preparation Method 46 was used to manufacture a battery which had a simple structure, which could be assembed simply and which had a cross sectional shape schematically shown in <figref idref="f0001">Fig. 2</figref>.

In an atmosphere of dry argon gas, the negative pole activating material 201 was used in such a manner that the titanium mesh collector 200 was pressed against the reverse side of the lithium metal foil. Then, the surface of lithium was covered with a fluororesin thin film by using thin solution of Lumiflon, which was a fluororesin paint manufactured by Asahi Glass, so that the negative electrode was manufactured.

Acetylene black powder and xylene solution of the Lumiflon, which was a fluororesin paint manufactured by Asahi Glass, were mixed with the positive electrode active material which was prepared by Preparation Methood 46 and which was lithium-manganese oxide. The mixture was applied to the titanium mesh, and it was hardened at 80°C, and then heated with microwaves. As a result, the positive pole 203 was formed.

The electrolytic solution was prepared by dissolving, by 1 M (mol/l), boronic acid tetrafluoride lithium salt in an equal quantity mixture solvent of propylene carbonate (PC) and dimethoxyethane (DME).

The separator 208 was manufactured in such a manner that a polypropylene separator having small apertures was sandwiched by unwoven polypropylene sheets.

The assembly was performed in such a manner that the separator 208 was sandwiched between the negative electrode 201 and the positive electrode 203, followed by inserting them into a positive electrode case 207 made of titanium clad stainless steel. Then, the electrolyte solution was injected. Then, the negative electrode cap 206 made of the titanium clad stainless steel and the insulating packing 210 made of fluorine rubber were used for sealing so that the lithium secondary battery was manufactured.

Example 47

The vanadium oxide prepared by Preparation Method 47 was used as the positive electrode active material, a battery having a cross sectional shape schematically shown in <figref idref="f0001">Fig. 2</figref> was manufactured.

First, the nickel mesh collector was pressed against the reverse side of the lithium metal foil in an atmosphere of dry argon gas so that the negative electrode was manufactured.

Acetylene black powder and Super Konak F which was a fluororesin paint manufactured by Nihon-Yushi were mixed with the vanadium oxide serving as the positive electrode activating material and prepared by Preparation Method 2, followed by adding xylene by a small quantity. The mixture was applied to the nickel mesh, and it was hardened at 150°C. As a result, the positive electrode was manufactured.

Then, similar processes to those according to Example 46 were performed so that the lithium secondary battery shown in <figref idref="f0001">Fig. 2</figref> was assembled.

Example 48

By using the positive electrode active material prepared by Preparation Method 48, a battery which had a simple structure, which could be assembled simply and which had a cross sectional shape schematically shown in <figref idref="f0001">Fig. 2</figref> was assembled.

First, the nickel mesh collector was pressed against the reverse side of the lithium metal foil in an atmosphere of dry argon gas so that the negative electrode was manufactured.

Acetylene black powder and tetrafluoroethylene polymer powder were mixed with the lithium-nickel oxide prepared by Preparation Method 48 and serving as the positive electrode active material. The mixture was pressed against the nickel mesh with heat as to be formed into the positive electrode 203.

Then, similar processes to those according to Example 46 were performed so that the lithium secondary battery shown in <figref idref="f0001">Fig. 2</figref> was assembled.

Example 49

The lithium-nickel-cobalt oxide prepared by Preparation Method 49 was used as the positive electrode active material so that the battery shown in <figref idref="f0001">Fig. 2</figref> was manufactured by the process similar to that according to Example 48.

Example 50

The vanadium-molybdenum oxide prepared by Preparation Method 50 was used as the positive electrode active material so that the battery shown in <figref idref="f0001">Fig. 2</figref> was manufactured by the process similar to that according to Example 48.

Example 51

The vanadium-molybdenum oxide prepared by Preparation Method 51 was used as the positive electrode active material so that the battery shown in <figref idref="f0001">Fig. 2</figref> was manufactured by the process similar to that according to Example 48.

Example 52

The titanium sulfide prepared by Preparation Method 52 was used as the positive electrode active material so that the battery shown in <figref idref="f0001">Fig. 2</figref> was manufactured by the process similar to that according to Example 48.

Example 53

The lithium-iron-cobalt oxide prepared by Preparation Method 53 was used as the positive electrode active material so that the battery shown in <figref idref="f0001">Fig. 2</figref> was manufactured by the process similar to that according to Example 48.

Example 54

The manganese containing magnesium added thereto-vanadium oxide prepared by Preparation Method 54 was used as the positive electrode active material so that the battery shown in <figref idref="f0001">Fig. 2</figref> was manufactured by the process similar to that according to Example 48.

Example 55

The lithium-copper-cobalt oxide prepared by Preparation Method 55 was used as the positive electrode active material so that the battery shown in <figref idref="f0001">Fig. 2</figref> was manufactured by the process similar to that according to Example 48.

Comparative Example 46

By using the positive electrode active material prepared by Comparative Preparation method 46, the battery having a cross sectional shape schematically shown in <figref idref="f0001">Fig. 2</figref> was manufactured.

First, the titanium mesh collector 200 was pressed against the reverse side of the lithium metal foil in an atmosphere of dry argon so that the negative electrode was manufactured.

Acetylene black powder and tetrafluoroethylene polymer powder were mixed to the lithium-manganese oxide prepared by Comparative Preparation Method 46 and serving as the positive electrode active material as to be, with heat, pressed and formed into the positive electrode 203.

Then, similar processes to those according to Example 46 were performed so that the lithium secondary battery was assembled.

Comparative Example 47

The vanadium oxide prepared by Comparative Preparation Method 47 was used as the positive electrode active material so that the battery shown in <figref idref="f0001">Fig. 2</figref> was manufactured by the process similar to that according to Example 48.

Comparative Example 48

The lithium-nickel oxide prepared by Comparative Preparation Method 48 was used as the positive electrode active material so that the battery shown in <figref idref="f0001">Fig. 2</figref> was manufactured by the process similar to that according to Example 48.

Comparative Example 49

The lithium-nickel-cobalt oxide prepared by Comparative Preparation Method 49 was used as the positive electrode active material so that the battery shown in <figref idref="f0001">Fig. 2</figref> was manufactured by the process similar to that according to Example 48.

Comparative Example 50

The vanadium-molybdenum oxide prepared by Comparative Preparation Method 50 was used as the positive electrode active material so that the battery shown in <figref idref="f0001">Fig. 2</figref> was manufactured by the process similar to that according to Example 48.

Comparative Example 51

The titanium sulfide prepared by Comparative Preparation Method 51 was used as the positive electrode active material so that the battery shown in <figref idref="f0001">Fig. 2</figref> was manufactured by the process similar to that according to Example 48.

Comparative Example 52

The lithium-iron-cobalt oxide prepared by Comparative Preparation Method 52 was used as the positive electrode active material so that the battery shown in <figref idref="f0001">Fig. 2</figref> was manufactured by the process similar to that according to Example 48.

Comparative Example 53

The manganese containing magnesium added thereto-vanadium oxide prepared by Comparative Preparation Method 53 was used as the positive electrode active material so that the battery shown in <figref idref="f0001">Fig. 2</figref> was manufactured by the process similar to that according to Example 48.

Comparative Example 54

The lithium-copper-cobalt oxide prepared by Comparative Preparation Method 54 was used as the positive electrode active material so that the battery shown in <figref idref="f0001">Fig. 2</figref> was manufactured by the process similar to that according to Example 48.

Evaluation of Performance of Lithium Secondary Battery

The performance of lithium secondary batteries according to Examples and Comparative Examples was evaluated. The evaluation was performed by a charge and discharge cycle test under the following conditions with respect to the cycle life of the batteries according to Comparative Examples.

The conditions for the cycle test were made as follows: the charge and discharge was performed by 0.2C (electric current which was 0.2 times capacity/time), pause for 30 minutes and a cut-off voltage of 1.0V was applied. A charging/discharging apparatus HJ-101M6 manufactured by Hokuto Electric was used. The charge/discharge test was commenced at discharge, the battery capacity was evaluate the quantity of the third discharge and the cycle life was evaluate by the number of cycles when the battery capacity had deteriorated to 60% or less.

The lithium batteries using the positive electrode active materials respectively according to the present invention and the comparative examples, that is, the battery capacities and cycle life of the examples of the present invention and the comparative examples were evaluated as shown in Table 12 while making the performance of the battery according to the comparative example to be a reference value of 1.

As can be understood from Table 12, the comparisons made between Examples 46 to 55 and Comparative Examples 46 to 54 resulted that the use of the batteries according to the present invention enabled the capacity of the battery to be enlarged and the cycle life to be lengthened. <tables id="tabl0001" num="0001"><table frame="all"><title>Table 12</title><tgroup cols="4"><colspec colnum="1" colname="col1" colwidth="21mm" /><colspec colnum="2" colname="col2" colwidth="41mm" /><colspec colnum="3" colname="col3" colwidth="52mm" /><colspec colnum="4" colname="col4" colwidth="53mm" /><thead><row><entry namest="col1" nameend="col2" align="center" valign="middle">Lithium Battery Manufactured</entry><entry morerows="1" valign="top">Capacity of Battery (Present Invention/ Comparative Example)</entry><entry morerows="1" valign="top">Cycle life (Present Invention/ Comparative Example)</entry></row><row><entry align="center" valign="middle">Examples</entry><entry valign="middle">Comparative Examples</entry></row></thead><tbody><row><entry align="center" valign="middle">Example 46</entry><entry valign="middle">Comparative Example 46</entry><entry valign="middle" align="char" char=".">2.3</entry><entry valign="middle" align="char" char=".">4.8</entry></row><row><entry align="center" valign="middle">Example 47</entry><entry valign="middle">Comparative Example 47</entry><entry valign="middle" align="char" char=".">3.1</entry><entry valign="middle" align="char" char=".">3.2</entry></row><row><entry align="center" valign="middle">Example 48</entry><entry valign="middle">Comparative Example 48</entry><entry valign="middle" align="char" char=".">2.1</entry><entry valign="middle" align="char" char=".">1.7</entry></row><row><entry align="center" valign="middle">Example 49</entry><entry valign="middle">Comparative Example 49</entry><entry valign="middle" align="char" char=".">2.0</entry><entry valign="middle" align="char" char=".">1.4</entry></row><row><entry align="center" valign="middle">Example 50</entry><entry valign="middle">Comparative Example 50</entry><entry valign="middle" align="char" char=".">4.1</entry><entry valign="middle" align="char" char=".">2.9</entry></row><row><entry align="center" valign="middle">Example 51</entry><entry valign="middle">Comparative Example 50</entry><entry valign="middle" align="char" char=".">3.2</entry><entry valign="middle" align="char" char=".">2.1</entry></row><row><entry align="center" valign="middle">Example 52</entry><entry valign="middle">Comparative Example 51</entry><entry valign="middle" align="char" char=".">2.4</entry><entry valign="middle" align="char" char=".">1.4</entry></row><row><entry align="center" valign="middle">Example 53</entry><entry valign="middle">Comparative Example 52</entry><entry valign="middle" align="char" char=".">2.3</entry><entry valign="middle" align="char" char=".">1.5</entry></row><row><entry align="center" valign="middle">Example 54</entry><entry valign="middle">Comparative Example 53</entry><entry valign="middle" align="char" char=".">1.7</entry><entry valign="middle" align="char" char=".">2.0</entry></row><row><entry align="center" valign="middle">Example 55</entry><entry valign="middle">Comparative Example 54</entry><entry valign="middle" align="char" char=".">2.2</entry><entry valign="middle" align="char" char=".">1.8</entry></row></tbody></tgroup></table></tables>

Further, combinations of the embodiments of the present invention will enable further improved secondary battery to be obtained.

According to the present invention, if dendrites of lithium grow at the time of charge, short circuits between the negative electrode and the positive electrode can be prevented. Therefore, a lithium secondary battery exhibiting a long charge/discharge cycle life can be manufactured. Further, the metal lithium can be used as the negative electrode active material. Therefore, a secondary battery exhibiting a high energy density can be manufactured while improving safety.

Although the invention has been described in its preferred form with a certain degree of particularly, it is understood that the present disclosure of the preferred form can be changed in the details of construction and the combination and arrangement of parts may be resorted to without departing from the scope of the invention as hereinafter claimed.