Electric separator, method for making same and use thereof in high-power lithium cells

Translation of description of equivalent WO 2004021499 A2

Electrical separator. Process for its preparation and use in high-capacity batteries, lithium

An electrical separator is a separator to be used in batteries and other devices in which electrodes, for. Example, while maintaining ion conductivity of each other must be separated.

The separator is customarily a thin porous insulating material possessing high ion permeability, good mechanical strength and long-term stability in the system, z. B. in the electrolyte of the battery, chemicals used and solvents. In batteries, the cathode from the anode fully electronically insulate but be permeable to the electrolyte. He also has to be permanently elastic and follow movements in the system, z. B. in the electrode pack during charging and discharging.

The separator largely determines the life of the assembly, in which it is used, eg. As the battery cells. The development of rechargeable batteries is therefore marked by the development of suitable separator.

General information about electrical separators and batteries can be found eg. B. at JO Besenhard in "Handbook of Battery Materials" (NCH-Nerlag, Weinheim 1999).

Separators at present consist predominantly of porous organic polymeric films or of inorganic nonwovens such. As nonwovens of glass or ceramic materials or else ceramic papers. These are produced by various companies. Major producers are: Celgard, Tonen, Practice, Asahi, Binzer, Mitsubishi, Daramic and others. A typical organic separator consists for. Example of polypropylene or of a polypropylene / polyethylene / polypropylene composite.

Disadvantages of these organic polyolefin are their relatively low thermal stability of well below 150 ° C as well as their low chemical stability in inorganic lithium battery cells. The Polyolefϊne used are the lithium batteries upon contact of the separator with the lithium or the lithiated graphite slowly attacked. For systems with a polymer electrolyte, it therefore leads to the formation of a dense oxidation product layer, which prevents further destruction of the separator in Li-ion batteries.

There are first attempts to use inorganic composite materials as separators. As in DE 198 38 800 an electrical separator is described, which comprises a sheet, provided with a plurality of openings, flexible substrate having a coating thereon, which is characterized in that the material of the substrate is selected from metals, alloys, plastics glass and carbon fiber, or a combination thereof, and the coating is a two-dimensionally continuous porous, electrically non-conductive ceramic coating. The separators, which have a support of electrically conductive material (as indicated in the example), however, have been found to be unsuitable for lithium ion cells, because the coating in the thickness described can not be produced on a large area without flaws and it makes it much easier to shorts comes.

In summary it can be stated that there is at present no suitable separator, with which one can produce particular wound inorganic high performance or high energy batteries cost.

In previous work (DE 101 42 622) it could be shown that this is feasible with a material comprising a sheet, provided with a plurality of openings, flexible substrate having an on and in said substrate coating, wherein the material of the substrate is selected from woven or non-woven electrically conductive fibers of glass or ceramic or a combination of such materials and the coating being a porous electrically insulating ceramic coating, and wherein the resulting separator has a thickness of less than 100 microns and is bendable, a in communication with the electrolyte sufficiently low resistance while having a sufficiently high long-term stability. For a variety of applications, the resistance of these separators, however, is still too high, because as the carrier, a glass fabric is used, which is firstly too thick and secondly has a too low porosity. It is desirable to also be able to use a same thermally and chemically resistant separator. It was therefore an object of the present invention a provide separator which is more thermally stable than known up to now polymeric separators.

In the further optimization of the properties of the separators described in DE 101 42 622 has been found that separators can be realized with the mentioned properties, when polymeric substrate materials are used. This provides electrical separators comprise a sheet, provided with a plurality of openings, flexible substrate having a coating on and in said substrate, wherein the material of the substrate being selected from non-woven electrically nonconductive fibers of polymers and said coating a porous electrically insulating ceramic coating. The separator has a thickness of less than 80 .mu.m, is bendable and displays in connection with an electrolyte, a sufficiently low resistance and also has a sufficient long-term durability. The chemical resistance to strong bases are obtained by use of stable polymers such. As polypropylene / polyethylene or polyacrylonitrile nonwoven and resistant ceramic materials such as ZrO₂ and TiO₂, Although the separators described in the as yet unpublished application DE 102 08 277 are very well suited to the tasks described, we found that the separators described there but are not particularly well suited for use in high power lithium batteries because these batteries in no time at nearly constant voltage large currents must be issued. Therefore, the separators described in DE 102 08 277 to meet the performance requirements of such separators for high power lithium batteries probably not because they have too low a porosity and large thickness and, consequently, a still too low ionic conductivity.

It was therefore an object of the present invention to provide a separator which is suitable for use in high power lithium batteries. Thus, a separator is used for such a battery system, the separator must have a significantly improved porosity and as thin as possible, so it was also an object of the present invention to provide a separator which has a higher porosity than prior art separators, but at the same time high mechanical and thermal stability comprises using the minimum thickness.

Surprisingly, it has been found that separators, the smaller a fleece having a thickness 30 microns, a porosity of more than 50% and a largely homogeneous pore radius distribution in which at least 50% of the pores have pore radii of 75 to 150 microns and in which the non-woven with an on and in the nonwoven porous inorganic coating is provided, which having bonded preferably with zirconium oxide or silicon oxide particles having a particle size of 0.5 to 7 microns, a high porosity, an ideal pore size and a small thickness with very good thermal, mechanical and chemical stability and therefore have significantly better as separators in lithium Hochleisτungsbatterien can be used.

The present invention therefore provides a separator comprising a flexible web having an on and in this non-woven porous inorganic coating, wherein the material of the nonwoven fabric is selected from non-woven electrically conductive polymer fibers, which is characterized in that the nonwoven has a thickness of less than 30 microns, a porosity of more than 50%, preferably 50 to 97% and a pore radius distribution having at least 50% of the pores have a pore radius of 75 to 150 microns.

Furthermore, object of the present invention is a method for producing a separator according to the invention, which is characterized in that a flexible non-woven, having a thickness of less than 30 microns, a porosity of 50 to 97% and a pore radius distribution in which at least 50% the pores have a pore radius of 75 to 150 microns, is provided on and in said substrate with a coating, wherein the material of the fabric is selected from non-woven electrically conductive polymer fibers.

Likewise, the present invention is the use of a separator according to the invention as a separator in high power lithium batteries and corresponding lithium high power batteries that have a separator of the invention.

In general it can be stated that - for the same porosity and Tortousität - the larger the pores in the separator are the lower is the be-adjusting resistance of the separator impregnated with electrolyte. Moreover, by choosing appropriate particle porosity of the separator are affected, resulting in the same way amended properties. One characteristic frequently used in this context, a separator is the Gurley number. It is a measure of the gas permeability of the dry porous separator. As described by O. Besenhard in "Handbook of Battery Materials", it can be concluded directly from the Gurley number on the conductivity of a known system. More generally it can be stated that a greater gas permeability (ie, smaller Gurley number) a higher conductivity for the wetted separator causes in the battery cell. the values ​​of Gurley number of commercially available separators are 10 to 50 when the pore diameter is about 0.1 microns, and wherein 20 to 100, when the pore diameter is 0.05 micrometers. ( G. Venugiopal; J. of Power Sources 77 (1999) 34- 41).

However, it is always to be aware that an exceptionally small Gurley number may also indicate defects, ie large holes, in the separator. These defects can in the operation of a battery lead to an internal short circuit. The battery can then very quickly discharged themselves in a dangerous reaction. This will produce such large electric currents that a closed battery cell can in the worst case can even explode. For this reason, the separator can contribute significantly to the safety or for the lack of security of Lithiumhochleistungs- or -hochenergie battery. Therefore, the separator is a crucial component in a battery and deserving great deal of attention.

Polymeric separators provide for example, the time required for lithium batteries certainty by preventing a certain temperature (the shutdown temperature is about 120 ° C) any current transport through the electrolyte. This is accomplished in that at this temperature the pore structure of the separator collapses and all the pores are closed. The fact that ions can no longer be transported, the dangerous reaction that can lead to an explosion comes to a halt. If the cell is due to external factors but further heated at about 150 to 180 ° C, the break-down temperature is exceeded. From this temperature, the separator melts, said contracts. at many locations in the battery cell, there is a direct contact between the two electrodes and thus a large area internal short circuit. This leads to an uncontrolled reaction that a Explosion of the cell ends, or the resultant pressure is (a bursting disk) often degraded by a pressure relief valve of fire.

In the hybrid, ie inorganic components and polymeric carrier material having a separator according to the invention it comes to shutdown (shutdown) when the high temperature melts the polymer structure of the carrier material and penetrates into the pores of the inorganic material, thereby closing them. For so-called Melt Down (collapse) occurs in the separator of the invention is not. Thus, the separator of the invention meets the requirements, voiced by various battery manufacturers safety shutdown by the shutdown mechanism in the battery cells. The inorganic particles ensure that there can never be a meltdown. This ensures that there are no operating states where large-area short circuit can occur.

If an additional Shut down mechanism (shutdown) is imperative for the application, this can also be achieved by equipping the surface and / or the pores of the ceramic or hybrid separator of the invention are provided with a substance which when reaching the temperature limit closes the pores and prevents continued ion flux. This can for example be achieved by a polymer or a wax whose melting point is in this range.

Even when an internal short circuit, the z. B. was caused by an accident, the separator of the invention is very safe. . Would be eg drill a nail by a battery occurs depending separator following: The polymer separator would at the puncture (a short-circuit current flows through the nail and causes it to heat up) melt and shrink. Thus, the short-circuit location will become larger and the reaction goes out of control. In the hybrid separator of the invention melts at best the polymeric substrate material, but not the inorganic separator material. Thus, the reaction in the interior of the battery cell following such an accident much more moderately. This battery is thus distinctly safer than one with a polymeric separator. This is particularly important in mobile applications in particular.

In addition, the separator of the invention has a distinct cost advantage over Separators based on glass or ceramic fabrics as z. B. DE describes 101 42 622. This is in addition to the significantly different material costs, among other things, that the polymer substrate is much easier to handle than glass or ceramic fabric, which still has a certain brittleness and is destroyed by careless handling. The entire production process is therefore complicated and therefore costly.

By the nature of the fabric used, which has a particularly suitable combination of thickness and porosity, separators can be made ​​that can be the requirements for separators in high-performance batteries, especially lithium batteries high performance requirements. The simultaneous use of in their precisely coordinated r particle size oxide particles for producing the porous ceramic coating has a very high porosity of the final separator is achieved, the pores are still small enough to prevent a penetration by lithium whiskers through the separator ,

To achieve an ideal pore size or porosity for the separator, it has proven to be particularly advantageous, the oxide films prior to suspend classify by winnowing, to ideally equal-sized oxide particles, since often a not commercially available metal particles inconsiderable proportion of particles which are significantly smaller than the average particle size. The presence of a large number of small particles has the consequence that the pores are partially reduced by these small particles or completely closed. The ideal pore size or porosity of the separator is then not always reach.

A hydroclassification in the form of a wet screening can also be carried out to separate to large particles. The coarse fraction of up to 5 wt .-% of the total amount of powder has, in the worst case, particles which are greater than the total thickness of the separator. These powders can not perform error-free coatings. Consequently, these have to be removed in any case. The maximum particle size is preferably from 1/3 to 1/5, and particularly preferably less than or equal to 1/10 of the nonwoven thickness.

Further, the particle-containing suspensions (slurry) can Klassierzentrifugation so be separated that case exclusively to the ideal particle fraction, which also has a fairly narrow particle size distribution.

Due to the high porosity in combination with the small thickness of the separator, it is also possible to soak the separator completely or at least almost completely with the electrolyte, so can that no dead spaces occur in some areas of the separator and thus in certain windings or layers of the battery cells where no electrolyte exists. This is achieved in particular in that the separators are free or substantially free of closed pores by observing the particle size of the oxide particles, in which the electrolyte can not penetrate.

The separators according to the invention also have the advantage that attach to the inorganic surface of the separator, the anions of the conductive salt partially, leading to an improvement in dissociation and thus to a better ionic conductivity in the high current range. Another not inconsiderable advantage of the inventive separator is in very good wettability. Due to the hydrophilic ceramic coating wetting with electrolytes is very rapid, which also leads to a slightly improved conductivity.

Summarizing, the advantages of the separator according to the invention for use in Hochleisungs lithium-ion batteries to:

♦ High porosity

♦ Ideal pore width

♦ Low thickness of the separator ♦ Low grammage

♦ Very good wetting behavior

♦ Improved dissociation of the electrolyte salt

The separator according to the invention and a method for its preparation is described below, without the invention being restricted to these embodiments.

The erfϊndungsgemäße separator comprising a flexible fabric having on and in this Nonwoven located porous inorganic coating, wherein the material of the nonwoven fabric is selected from non-woven electrically conductive polymer fibers, is characterized in that the nonwoven has a thickness of less than 30 microns, a porosity of more than 50%, preferably 50-97 % and a pore radius distribution having having at least 50% of the pores have a pore radius of 75 to 150 microns.

Particularly preferably, the inventive separator comprises a nonwoven fabric having a thickness of 5 to 30 microns, preferably a thickness of 10 to 20 microns. Especially important for use in a separator according to the invention a homogeneous pore radius distribution is shown in the web above. An even more homogeneous pore radius distribution in the nonwoven in conjunction with optimally adapted oxide particles of a certain size to an optimized porosity of the separator according to the invention.

Preferably, the nonwoven has a porosity of 60 to 90%, particularly preferably from 70 to 90%. The porosity is defined as the volume of the nonwoven (100%) minus the volume of the fibers of the web, so the share of the volume of the nonwoven which is not taken up by material. The volume of the nonwoven can be calculated from the dimensions of the mat. The volume of the fibers is calculated from the measured weight of the nonwoven and the density of the polymer fibers. The high porosity of the substrate allows a higher porosity of the hybrid separator according to the invention, therefore, a higher intake of electrolytes can be achieved with the separator according to the invention. Preferred webs are webs of polymer fibers.

Thus, a separator having insulating properties can be obtained, that includes, as polymer fibers for the nonwoven is preferably not electrically conductive fibers of polymers which are preferably selected from polyacrylonitrile (PAN), polyesters such. As polyethylene terephthalate and / or polyolefin (PO ), such as, for example, polypropylene (PP) or polyethylene (PE) or blends of such polyolefins. The polymeric fibers of the nonwoven materials preferably have a diameter of 0.1 to 10 microns, more preferably 1-4 microns. Particularly preferred flexible webs have a basis weight of less than 20 g / m², Preferably from 5 to 10 g / m² on. The separators according to the invention preferably have a thickness of less than 35 microns, preferably less than 25 microns, more preferably a thickness of 15 to 25 .mu.m. The thickness of the substrate has a great influence on separator properties, since not only the flexibility but also the sheet resistance of the electrolyte-saturated separator is dependent on the thickness of the substrate. The low thickness provides a particularly low electrical resistance of the separator in use is achieved with an electrolyte. The separator itself naturally has a very high electrical resistance, since it has to have insulating properties. Moreover, thinner separators permit an increased packing density in a battery stack, so you can store a larger amount of energy in the same volume.

The separator according to the invention on and in the mat comprises a porous electrically insulating ceramic coating. Preferably, the on and in the nonwoven porous inorganic oxide coating particles of the elements Al, Si and / or Zr having an average particle size of 0.5 to 7 microns, preferably from 1 to 5 microns and most preferably from 1.5 to 3 .mu.m. Particularly preferably, the separator has a nonwoven on and in the porous inorganic coating on which alumina particles having an average particle size of 0.5 to 7 microns, preferably from 1 to 5 microns and most preferably from 1.5 to 3 microns which are bonded with an oxide of the elements Zr or Si. In order to achieve a very high porosity, more than 50 wt .-% and particularly preferably more than 80 wt .-% of all particles are preferably in the above-mentioned limits for the average particle size. As described above, the maximum particle size is preferably 1/3 to 1/5 and more preferably less than or equal to 1/10 of the thickness of the nonwoven used.

Preferably, the separator has a porosity of 30 to 80%, preferably from 40 to 75% and particularly preferably from 45 to 70%. Porosity refers to the accessible, ie open pores. The porosity can be determined by the familiar method of mercury porosimetry or can be calculated from the volume and the density of the materials used, if it is assumed that there are only open pores. The inventive separators are characterized by the fact that they may have a tensile strength of at least 1 N / cm, preferably at least 3 N / cm and most preferably from 3 to 10 N / cm. The inventive separators can preferably without damage down to any radius down to 100 m, preferably down to 50 mm and most preferably down to 1 mm. The high breaking strength and the good bendability of the separator according to the invention has the advantage that during charging and discharging of a battery occurring changes in electrode geometry which is able to follow through the separator without being damaged. The flexibility also has the advantage that commercially standardized wound cells can be manufactured using this separator. In these cells, the electrode / separator plies are wound in a standard size with each spiral and contacted.

It may be advantageous if the separator has a noninherent shutdown mechanism. This can eg. B. be realized that a very thin wax or polymer particle layer is present on or in the separator, which melt at a desired shutdown, so-called shutdown. Particularly preferred materials from which the shutdown particles include for example natural or artificial waxes or low-melting polymers, such. As polyolefins, the material for the shutdown is selected so that the particles melt at the desired shutdown and the pores of the separator closed so that further ion flux is prevented.

Preferably, the shutdown have a mean particle size (D_w) Which is greater than or equal to the average pore size (d_s) Of the pores of the porous inorganic layer of the separator is. This is particularly advantageous because this prevents penetration and closing the pores of the separator, which would result in a reduction of the pore volume and thus the conductivity of the separator and also the performance of the battery the consequence is prevented. The thickness of the shutdown is only critical insofar as it would an excessively thick layer increase the resistance in the battery system unnecessarily. In order to achieve a safe shutdown, the shutdown should have a thickness (z_w) Which is approximately in the mean particle size of the shutdown (D_w) Up to 10 D_w, Preferably from 2 D_w to D_w is. A thus equipped separator has a primary Safety feature on. In contrast to the purely organic separator, this separator can not melt completely, however, and it can never be a meltdown. These security features are very important because of the very large amounts of energy for high energy batteries and therefore are frequently mandated.

The separator according to the invention is preferably obtainable by a process for producing a separator, which is characterized in that in or on a flexible web having a thickness of less than 30 microns, a porosity of more than 50%, preferably from 50 to 97% and having a pore radius distribution having at least 50% of the pores have a pore radius of 75 to 150 microns, by applying a suspension and heating at least once, wherein the suspension to and solidified in the nonwoven fabric, a porous inorganic coating is placed, wherein comprising the suspension metal oxide particles and at least one sol and the material of the nonwoven fabric is selected from non-woven electrically conductive polymer fibers. Preferably, the suspension of metal oxide particles having an average particle diameter of 0.5 to 7 microns, preferably from 1 to 5 microns and most preferably from 1.5 to 3 microns of the metals Al, Zr and / or Si and at least one sol.

The process itself is known in principle from WO 99/15262, however, not all the parameters and ingredients, especially non-electrically conductive materials used, using for the production of the separator according to the invention. In particular, the particles used for preparing the dispersion as well as the non-woven fabrics used as the substrate are quite different from the starting materials described previously.

The suspension may, for. Example, be brought by printing on, pressing in, rolling on, doctoring, brushing, dipping, spraying or pouring on in the fleece.

The nonwoven fabric used preferably has a thickness of less than 20 microns, preferably less than 15 microns and most preferably a thickness of 7.5 to 15 microns. Particularly preferably used are those non-woven fabrics, as described in the description of the separator according to the invention.

The nonwoven fabric used is preferably a web of polymeric fibers or a nonwoven fabric which z ^ urründest polymer fibers. The polymer fibers are preferably selected from polyacrylonitrile, polyester, such as. For example, polyethylene terephthalate, and / or polyolefins. But all other known polymeric fibers can be used, provided that they have both the necessary for producing the separators temperature stability are also stable under the operating conditions in the lithium battery. Preferably, the separator of the invention comprises polymeric fibers having a softening temperature of above 100 ° C and a melting temperature of greater than 110 ° C. It may be advantageous if the polymer fibers have a diameter of 0.1 to 10 microns, preferably 1-5 microns.

The suspension used for coating comprises at least one sol of the elements Al, Zr and / or Si, and is prepared by suspending oxide particles in at least one of these sols. The brine can be obtained by hydrolyzing at least one compound with water or an acid or a combination thereof. It may be advantageous to be hydrolyzed compound before hydrolysis into alcohol or an acid or a combination thereof. As a compound to be hydrolyzed, a nitrate, a chloride, a carbonate, an alkoxide of the elements Al, Zr and / or Si is hydrolyzed preferably at least. The hydrolysis is preferably carried out in the presence of water, water vapor, ice or an acid or a combination thereof.

In one embodiment of the inventive process, particulate sols are prepared by hydrolysis of the compounds to be hydrolyzed. These particulate sols are distinguished in that in the sol compounds formed by hydrolysis are present in particulate form. The particulate sols can be prepared as described above or as described in WO 99/15262. These sols customarily have a very high water content, which is preferably greater than 50 wt .-%. It may be advantageous to be hydrolyzed compound before hydrolysis into alcohol or an acid or a combination thereof. The hydrolyzed compound may be peptized with at least one organic or inorganic acid, preferably with a 10 to 60% organic or inorganic acid, particularly preferably treated with a mineral acid selected from sulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid and nitric acid or a mixture of these acids will. The thus prepared particulate sols can be used for the preparation of suspensions subsequently, wherein the preparation of suspensions for application to polymeric sol pretreated with polymeric fibrous webs being preferred.

In a further embodiment of the method according to the invention, polymeric sols are prepared by hydrolysis of the compounds to be hydrolyzed. In this preferred embodiment of the method according to the invention, the sol has a fraction of water and / or acid from less 50 wt .-%. These polymeric sols are distinguished in that in the sol compounds formed by hydrolysis polymer (ie catenary networked over a wider area) present. Polymeric sols usually less than 50 wt .-%, and preferably much less than 20 wt .-% of water and / or aqueous acid. To obtain the preferred fraction of water and / or aqueous acid, the hydrolysis is preferably carried out so that the compound to be hydrolyzed with 0.5 to ten-fold molar ratio and preferably with half the molar ratio of water, water vapor or ice, based on the hydrolyzable group of the hydrolyzable compound is hydrolyzed. An up to tenfold amount of water can be used at very slow to hydrolyze, such. As tetraethoxysilane. Very quick to hydrolyze compounds such as zirconium tetraethoxide can form particulate sols, so to hydrolyze such compounds preferably 0.5 times the amount of water is used under these conditions thoroughly. A hydrolysis with less than the preferred amount of water, water vapor or ice likewise leads to good results. Although using the preferred amount of half the molar ratio greater than 50% is possible but not very useful because when it falls below this value, the hydrolysis is no longer complete and coatings based on such sols are not very stable.

For the production of sols having a desired very low proportion of water and / or acid in the sol, it may be advantageous if the compound to be hydrolyzed in an organic solvent, in particular ethanol, isopropanol, butanol, amyl alcohol, hexane, cyclohexane, ethyl acetate and or mixtures of these compounds, is achieved before the actual hydrolysis is carried out. A sol thus prepared can be used for preparing the suspension according to the invention. Both particulate sols (high water content, low solvent content) and polymeric sols (low water content, high solvent content) can be used as a sol in the process for producing the inventive suspension. As well as sols obtainable as just described, also commercially available sols such. Example zirconium nitrate sol or silica can be used in principle. The process of preparing separators by applying and solidifying a suspension on a support in itself is known from DE 101 42 622 and in similar form from WO 99/15262, however, not all the parameters and ingredients, in the manufacture of transmitted inventive membrane. The process, which is described in WO 99/15262, particularly not without fully applicable to polymeric nonwoven materials transferable in this form, as outlined therein very watery sol systems, often do not allow for continuous wetting of the customarily hydrophobic polymeric nonwovens in depth, since the very watery sol systems not only badly wetted most polymeric nonwovens. It was found that even the most minute non-wetted areas in the nonwoven material to membranes or separators being obtained that have defects and hence are inutile.

It has now surprisingly been found that a sol system or a suspension, which was and which adapted to the polymers wetting behavior, the nonwoven materials completely saturated and therefore error-free coatings. it is therefore preferable in the present process to adapt the wetting behavior of the sol or suspension. This is preferably accomplished by the preparation of sols or suspensions, these sols comprise one or more alcohols, such as. For example, methanol, ethanol or propanol or mixtures thereof, and / or aliphatic hydrocarbons, include. However, other solvent mixtures are conceivable, which may be the sol or suspension added to adjust to the nonwoven used in networking behavior.

the mass fraction of the suspended component is preferably (metal oxide particles) of the suspension contains 1 to lOOfache, particularly preferably 1 to 50 times, and most preferably 1 to the tenfold of the sol used. the suspension of metal oxide particles alumina particles are particularly preferably used for the preparation, preferably having a mean particle size of 0.5 to 7 microns. Alumina particles be in the range of the preferred particle sizes, for example, by the company Martin under the designations MDS 6; DN 206, MZS 3 and MZS 1 and offered by the company. Alcoa called CL3000 SG, CT800 SG and HVA SG.

It has been found that the use of commercially available metal oxide particles may lead to unsatisfactory results since frequently very large particle size distribution. There metal oxide particles are therefore preferably used, which were classified by a conventional method, such. As wind sifting, centrifuging and hydroclassification. Such groups are preferably used as a metal oxide, in which the coarse fraction, which accounts for up to 10% of the total, was separated by wet screening. This disturbing coarse fraction, which can not or only with difficulty be crushed by the typical in the production of slurry processes such as grinding (ball mill, attrition mill, mortar mill), dispersing (Ultra-Turrax, ultrasound), trituration or chopping, z can. B. consist of aggregates, hard agglomerates, grinding media attritus. The aforementioned measures it is achieved that the inorganic porous layer has a very uniform pore size distribution. This is achieved in particular in that the metal oxide particles are used which have a maximum particle size of preferably from 1/3 to 1/5 and more preferably less than or equal to 1/10 of the thickness of the nonwoven used.

The following Table 1 gives an overview of how the choice of the various aluminum oxides affects the porosity and the resulting pore size of the respective porous inorganic coating. In order to determine this data, the corresponding slips (suspensions) were prepared and dried as pure moldings at 200 ° C and solidified.

Table 1: Typical data of ceramics depending on the used powder type

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To improve the adhesion of the inorganic components to polymeric fibers as a substrate, it may be advantageous to administer suspensions used adhesion promoters such. B. accompanied organo-functional silanes. As adhesion promoters, in particular compounds selected from the octylsilanes, the vinyl silanes, the amine-functionalized silanes and / or the glycidyl-functionalized silanes such. B. Degussa are the Dynasilanes from. Usable. Particularly preferred adhesion promoters for polyethylene (PE) and polypropylene (PP) are vinyl, methyl and octylsilanes, wherein an exclusive use of methylsilanes is not optimal, for polyamides and polyamines are Aminfünktionelle silanes, for polyacrylates and polyesters, there are glycidyl fünktionalisierte silanes and for polyacrylonitrile also possible to use glycidyl silanes. Other adhesion promoters can be used, but must be matched to the respective polymers. The adhesion promoters have to be chosen such that the solidification temperature is below the melting or softening of the polymer used as the substrate and below its decomposition temperature. Preferably, suspensions according to the invention very much less than 25 wt .-%, preferably less than 10 wt .-% compounds which can function as adhesion promoters. An optimal fraction of adhesion promoter results from coating the fibers and / or particles with a monomolecular layer of adhesion promoter. The purpose required amount of bonding agent in grams, by multiplying the amount of the oxides used, or the fiber (in g) with the specific surface area of ​​the materials (in m²G^_1) And then dividing by the specific area required by the adhesion promoters (in m² G^"1) Are obtained, wherein the specific area required frequently in the order of 300 to 400 mg^" lies.

Table 2 below contains an illustrative overview of usable adhesion promoters based on organofunctional Si compounds for typical nonwoven material polymers. Table 2

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With:

AMEO 3-aminopropyltriethoxysilane = DAMO = 2-aminoethyl-3-aminopropyltrimethoxysilane

GLYMO = 3 glycidyloxytrimethoxysilane

MEMO = 3-methacryloxypropyltrimethoxysilane

Silfin = vinylsilane + initiator + catalyst

VTEO = vinyltriethoxysilane VTMO = vinyltrimethoxysilane

VTMOEO = vinyltris (2-methoxyethoxy) silane

In a particular embodiment of the method the abovementioned adhesion promoters are applied in an upstream step on polymeric nonwoven (substrate). For this purpose the coupling agent in a suitable solvent, such. As dissolved ethanol. This solution may additionally include a small amount of water, preferably from 0.5 to tenfold amount based on the molar amount of the hydrolyzable group, and small amounts of an acid, such as., HCl or HNO, as a catalyst for the hydrolysis and condensation the Si-OR groups. By known techniques, such. As spraying, printing, Auφressen, pressing in, rolling on, doctoring, brushing, dipping, spraying or pouring this solution is applied to the substrate and the adhesive by a heat treatment at 50 to a maximum of 350 ° C on the substrate fixed. Only after the application of the adhesive takes place in this variant of the method the application and solidification of the suspension. By applying a primer before the actual application of the suspension, the adhesion behavior of the substrates can be improved, in particular to aqueous particulate sols, which is why so pretreated substrates with suspensions based on commercially available sols such. Example zirconium nitrate sol or silica sol can be inventively coated , But this way of applying an adhesion promoter also means that the production of the separator according to the invention has to be extended by an intermediate or pre-treatment step. This is feasible albeit more costly than the use of adapted sols to which adhesion promoters have been added, but also has the advantage that even when using suspensions based on commercially available sols better results.

The coatings of the invention are brought by solidifying the suspension on and in the web in and to the nonwoven. According to the invention which are solidified to and present in the nonwoven suspension by heating to 50 to 350 ° C. Since when using polymeric substrate materials are the maximum temperature is determined by the web, this is adjusted accordingly. So depending on the variant of the method according to the invention, the suspension on and in the nonwoven existing is solidified by heating at 100 to 350 ° C and very particularly preferably by heating to 110 to 280 ° C. It may be advantageous if the heating is carried out for 1 second to 60 minutes at a temperature of 100 to 350 ° C. More preferably, the heating to solidify the suspension to a temperature from 110 to 300 ° C., most preferably at a temperature of 110 to 280 ° C and preferably for 0.5 to 10 min.

The heating of the composite according to the invention can be carried out by means of heated air, hot air, infrared radiation or other heating methods according to the prior art.

The inventive method can be z. B. carried out so that the polymer fabric is unrolled as a substrate from a roll at a speed of 1 m / h to 2 m / s, preferably at a speed of 0.5 m / min. to 20 m / min and most preferably at a speed of 1 m min to 5 m / min through at least one apparatus that brings the suspension onto and into the substrate, such. as a roller, and at least one further apparatus on which the suspension is solidified, and in which allows support by heating, such. as by an electrically heated furnace and the separator thus produced up on a second roll. In this way it is possible to fabricate the separator according to the invention in a continuous process. The pretreatment steps may be performed in a continuous process while retaining the above-mentioned parameters.

It has proved to be particularly advantageous when the method is carried out so that the fleece, in particular the polymeric nonwoven during the coating process or coating processes having a maximum tension in the longitudinal direction of 10 N / cm, preferably of 3 N / cm. Under coating processes in this case be understood all the method steps, in which a material is brought to and into the substrate where it is solidified by heat treatment, including the application of the adhesion promoter. Preferably the substrate during the coating processes with a maximum force of 0.01 N / cm is stretched. Particularly preferably, it may be when the substrate during the coating process or coating processes is performed unstressed in the longitudinal direction.

By controlling the tension during the coating process can be avoided that a deformation (and elastic) of the carrier material takes place. Due to some deformation (elongation) at too high a tension, the ceramic coating can not follow the nonwoven material, resulting in that the coating is dissolved over the entire surface of the nonwoven material. The resulting product can then not be used as intended.

The separator according to the invention with an additional automatic shutdown mechanism be equipped, it z. B. can be done in that after solidification of the coating applied to the substrate suspension a layer of particles, which melt at a desired temperature and close the pores of the separator, so-called shut-down, is attached and fixed to generate a shut-off mechanism on the separator. The layer of shutdown can z. B. greater than the average pore size of the separator produced in a sol, water, solvent or solvent mixture by applying a suspension of waxy particles having an average particle size. The suspension for applying the particles preferably contains from 1 to 50 wt .-%, preferably from 5 to 40 wt .-% and very particularly preferably from 10 to 30 wt .-% of shut-down, and in particular wax particles in the suspension.

Since the inorganic coating of the separator often has a very hydrophilic nature, it has proven to be advantageous if the coating of the separator was prepared using a silane in a polymeric sol as a bonding agent and has thus been rendered hydrophobic. To achieve good adhesion and uniform distribution of the shutdown particles in the shutdown layer on hydrophilic hydrophobic porous inorganic separator, there are several possibilities.

In one embodiment of the method according to the invention, it has proven to be advantageous hydrophobing the porous inorganic layer of the separator before the application of the shutdown. The production of hydrophobic membranes which works on the same principle is described for example in WO 99/62624. Preferably, the porous inorganic coating is removed by treatment with alkyl, aryl or fluoroalkylsilanes marketed for. Example, under the tradename Dynasylan® from Degussa, hydrophobic. It can be, for example the familiar hydrophobicization methods which are employed inter alia for textiles (D. Knittel; E. Schollmeyer; Melliand Textilber (1998) 79 (5), 362-363.)., With minimal changes to the recipes are applied for the porous coatings of the separator. For this purpose, the coating or the separator is treated with a solution containing at least one hydrophobic material. It may be advantageous if the solution as solvent water, preferably with an acid, preferably acetic acid or hydrochloric acid, was adjusted to a pH of 1 to 3, and / or an alcohol, preferably ethanol. The proportion of acid-treated water or to alcohol solvents may be .-% each from 0 to 100 Vol. Preferably, the proportion of water in the solvent from 0 to 60 Vol .-% and the proportion of alcohol from 40 to 100 Vol .-%. In the solvent to create the solution contains 0.1 to 30 wt .-%, preferably 1 to 10 wt .-% of a hydrophobic substance added. Useful hydrophobic materials include. For example the silanes listed above are used. Surprisingly, good hydrophobicization is obtained not just with strongly hydrophobic compounds such as triethoxy (3,3,4,4,5,5,6,6,7,7,8,8-tridecafluorooctyl) silane, but a Treatment with methyltriethoxysilane or i-butyl-triethoxysilane is completely sufficient to achieve the desired effect. The solutions are stirred for uniform distribution of the hydrophobic materials in the solution, at room temperature and then applied to the inorganic coating on the separator and dried. Drying may be accelerated by treatment at temperatures from 25 to 100 ° C.

In another version of the process according to the invention, the porous inorganic coating can be treated prior to application of the shutdown with other bonding agents. The treatment with one of the below mentioned coupling agent can be effected as described above, then also, that the porous inorganic layer is treated with a polymeric sol comprising a silane adhesion promoter.

The layer of shutdown is preferably formed by applying a suspension of shutdown in a suspending agent selected from a sol, water or

Solvents, such as. For example, alcohol, ether, or ketone, or a solvent mixture formed on the inorganic coating of the separator and subsequent drying. The

Particle size of the present in the suspension to include shutdown is arbitrary in principle. However, it is advantageous for the suspension to include shutdown particles having an average particle size (D_w) Greater than or equal to, preferably greater than the average pore size of

Pores of the porous inorganic layer (d_s) Are present, because it ensures that the

Pores of the inorganic layer are not clogged by shutdown particles in the production of the separator according to the invention. Preferably, the shutdown particles used have an average particle size (D_w) Which is greater than the average pore diameter (d_s) And less than 5 d_s, More preferably less than 2 d_s is.

Should it employ shutdown, which have a particle size less than the size of the pores in the porous inorganic layer, it must be avoided that the particles penetrate into the pores of the porous inorganic separator layer. Reasons for the use of such particles can, for. Example, in large price differences, but also lie in the availability of such particles. One way to prevent the penetration of the shutdown in the pores of the porous inorganic layer is, the viscosity of the suspension so that in the absence of external shear forces occurs no penetration of the suspension into the pores of the inorganic layer of the separator. Such a high viscosity of the suspension can be achieved, for. Example, the fact that the suspension auxiliaries which influence the flow behavior, such as. For example, silicic acids (Aerosil, Degussa) are added. When auxiliaries such as. For example, Aerosil 200, a proportion of 0.1 to 10 wt .-%, preferably 0.5 to 50 wt .-% silica, based on the suspension, sufficient for a sufficiently high viscosity the suspension to achieve. The fraction of auxiliaries can in each case determined by simple preliminary.

It may be advantageous if the shutdown particle suspension used to contain adhesion promoters. Such suspension with adhesion promoter can be applied directly to an inorganic layer of the separator, even if this was not hydrophobicized beforehand. Of course, an adhesion promoter can also be applied to a hydrophobicized layer or to a separator, in whose preparation a bonding agent was used a suspension with. Adhesion promoters in the shutdown particle suspension preferably silanes having amino, vinyl or methacryloyl. Such adhesion promoters are, for. Example AMEO (3-aminopropyltriethoxysilane), MEMO (3-methacryloxypropyltrimethoxysilane), Silfin (vinylsilane + initiator + catalyst), VTEO (vinyltriethoxysilane) or VTMO (vinyltrimethoxysilane). Such silanes are z. B. by Degussa in aqueous solution under the name Dynasylan® 2926, 2907 or 2781.. A proportion of at most 10 wt .-% of adhesion promoter has been found to be sufficient for ensuring sufficient adhesion of the shutdown particles to the porous inorganic layer. Adhesion promoter preferably having Shutdown particle suspensions of 0.1 to 10 wt .-%, preferably from 1 to 7.5 wt .-% and most preferably from 2.5 to 5 wt .-%, based on adhesive to the suspension in ,

Useful shutdown all particles can be used, which have a defined melting point. The particle material is chosen according to the desired shutdown. Since relatively low shutdown temperatures are desired for most batteries, it is advantageous to use shutdown, which are selected from particles of polymers, polymer blends, natural and / or artificial waxes. Particularly preferred shutdown Particles of polypropylene or polyethylene wax used.

The application of the shutdown particle suspension can be done by printing, Auφressen, pressing in, rolling on, doctoring, brushing, dipping, spraying or pouring on the porous inorganic layer of the separator. The shutdown layer is preferably obtained in that the suspension applied is dried at a temperature of from room temperature to 100 ° C, preferably from 40 to 60 ° C.

It may be advantageous if the shutdown after application to the porous inorganic layer by heating at least once to a temperature above the glass transition temperature, so that a melting of the particles is achieved without changing the actual shape, fixed. In this way it can be achieved that the shutdown particles adhere particularly firmly to the porous inorganic separator layer.

The application of the shutdown particle suspension with subsequent drying and any heating to above the glass transition temperature can be carried out continuously or quasi-continuously. If a flexible separator used as a starting material, it can again be unwound from a roll, passed through a coating, drying and, if appropriate, heating apparatus and then rolled up again.

Hybrid separators according to the invention can be used as separators in batteries. In the inventive use of the separator as a separator in batteries, the separator is typically impregnated with the electrolyte between the anode and the cathode placed.

The separator according to the invention is for primary and secondary (rechargeable) lithium batteries, for nickel metal hydride, nickel-cadmium, silver-zinc, and suitable zinc-air batteries. Due to its particularly high porosity and large pores of the separator of the invention is particularly suitable for use in high power lithium batteries.

In addition to batteries having a separator according to the invention, therefore, are the subject the present invention particularly high performance lithium batteries comprising a separator according to the invention.

Also suitable are the inventive separators for use in batteries to be charged quickly. Such high-capacity batteries can be quickly charged and also discharged. are advantageous especially the optimized properties of the separator with regard to thickness, pore radius, porosity and thereby the high ionic conductivity of the electrolyte-saturated separator. The high temperature resistance of the separator of the invention is a battery that is equipped with this separator will not be so sensitive to temperature and can therefore withstand the temperature rise due to the rapid charging without adverse changes to the separator or damage to the battery. Consequently, these batteries must be recharged much faster.

This is a distinct advantage of using such equipped batteries in electric vehicles, since they no longer have to be charged for several hours, but recharging within ideally be carried out by one hour or less than an hour.

The present invention will be described by the following examples, without being limited thereto.

Example 1: Preparation of a S450PET Separator

To 160 g of ethanol 15 g of a 5 wt .-% aqueous HCl solution, 10 g Tefraethoxysilan, 2.5 g of methyltriethoxysilane and 7.5 g of Dynasylan® GLYMO are first (manufacturer of all Dynasilanes: Degussa AG) were added. This sol, which was initially stirred for some hours, then 125 g each of aluminum Martoxid MZS-1 and Martoxid MZS- be 3 (both aluminas Martinswerke). This slip is homogenized for at least another 24 hours with a magnetic stirrer, the mixing vessel must be covered so as to avoid loss of solvent.

A PET nonwoven having a thickness of about 30 microns and a basis weight of about 20 g / m is in a continuous roll coating process (belt speed of about 8 m / h, T = 200 ° C) coated with the above slurry. In this roll coating process, the slip is rolled with a roller turning opposite to the belt direction (the direction of movement of the nonwoven) moved to the web. The nonwoven subsequently passes through an oven having the temperature indicated. In the following experiments the same method or arrangement is used for coating. The end result is a separator having an average pore size of 450 nm and a thickness of about 50 microns. The Gurley number is about 6th

In parallel, a solid molding is produced, and also dried at 200 ° C and solidified with the above slurry. The porosity is about 47%, the average pore size 450 nm.

Example 2: Preparation of a S750PET separator

To 130 g of water and 30 g of ethanol were initially added 30 g of a 5 wt .-% aqueous HNO₃added: solution, 10 g of tetraethoxysilane, 2.5 g of methyltriethoxysilane and 7.5 g of Dynasylan® GLYMO (Degussa AG manufacturer of all Dynasilanes). This sol, which was initially stirred for some hours, then 260 g CL3000 SG will (make: AlCoA) suspended. This slip is homogenized for at least another 24 hours with a magnetic stirrer, the mixing vessel must be covered so as to avoid loss of solvent. Prior to coating this slurry is filtered through a 20 micron sieve to remove the coarse particle fraction.

A PET nonwoven having a thickness of about 15 microns and a basis weight of about 6 g / m (belt speed of about 8 m / h, T = 200 ° C) is thus coated with the above slip in a continuous roll coating. The end result is a separator having an average pore size of 755 nm and a thickness of 30 microns. The Gurley number is about. 3

In parallel, a solid molding is produced, and also dried at 200 ° C and solidified with the above slurry. The porosity is about 51%, the average pore size 755 nm. Example 3: Preparation of a S850PET separator

At 145 g of water and 15 g of ethanol were initially added 30 g of a 5 wt .-% aqueous HNO solution, 10 g Tefraethoxysilan, 2.5 g of methyltriethoxysilane and 7.5 g of Dynasylan® GLYMO (manufacturer of all Dynasilanes: Degussa AG), where , This sol, which was initially stirred for some hours, then 280 g HVA SG will (make: AlCoA) suspended. This slip is homogenized for at least another 24 hours with a magnetic stirrer, the mixing vessel must be covered so as to avoid loss of solvent. Prior to coating this slurry is filtered through a 15 micron sieve to remove the coarse particle fraction.

A PET fleece having a thickness of about 15 microns and a basis weight of about 6 g / m² is so (about 8 m / h, T = 200 ° C belt speed) coated in a continuous roll coating with above slip. The end result is a separator having an average pore size of 865 nm and a thickness of 30 microns. The Gurley number is about. 2

In parallel, a solid molding is produced, and also dried at 200 ° C and solidified with the above slurry. The porosity is about 53%, the average pore size 865 nm.

Example 4: Li-Ion Battery with Hybrid Ceramic Separator An established according to Example 1 S450PET separator is installed in a lithium ion cell consisting of a positive mass of LiCoO₂, A negative mass consisting of graphite and an electrolyte of LiPFβ in ethylene carbonate / dimethyl carbonate [LiCoO2 // S-450 PET, EC / DMC 1: 1, IM LiPF₆ // Graphite]. There, the charging and discharging of this battery was checked. The battery is facing about 250 cycles (charging / discharging at C / 5) only a small drop in capacity by a few percentage points. Even increasing the charging voltage from 4.1 to 4.2 volts in the 200th charge cycle does not harm the battery.

We this battery but with C (about 3 mA / cm²) Discharged so can not unload the entire capacity at these high currents. This is due to the still high internal resistance. Example 5: i-Ion Battery with Hybrid Ceramic Separator

A prepared in Example 3 S850PET separator is installed in a lithium ion cell consisting of a positive mass of LiCoO₂, A negative mass consisting of graphite and an electrolyte of LiPFβ in ethylene carbonate / dimethyl carbonate [LiCoO2 // S-450 PET, EC / DMC 1: 1, IM LiPF₆ // Graphite]. There, the charging and discharging of this battery was checked. The battery is facing about 250 cycles (charging / discharging at C / 5) only a small drop in capacity by a few percentage points. Even increasing the charging voltage from 4.1 to 4.2 volts in the 200th charge cycle does not harm the battery.

We unload this battery with C (about 3 mA / cm), it can be in these high currents virtually the entire capacity of the battery is discharged. This is the ιrückzuführen compared to Example 4, higher porosity, larger pore size smaller thickness and, associated with lower internal resistance. 2

This separator is therefore particularly well suited for high current battery.