High discharge capacity lithium battery

ES 2 304 697 T3

DESCRIPTION

Lithium battery with high discharge capacity.

Field of the invention

This invention relates to electrochemical battery cells, particularly cells with a negative lithium electrode and a positive iron disulfide electrode. In one embodiment, the positive electrode includes iron disulfide particles that have a specific range of small average particle sizes, which allows the electrochemical cell to display desirable properties for both low- and high-rate applications. The iron disulfide particles are formed by means of a wet or dry process, which reduces their particle size to a predetermined size range. In a preferred method of the invention, a cathode suspension comprising the iron disulfide particles is milled using a "media mill" media mill that reduces the iron disulfide particles to a desired average particle size range, to its incorporation into the positive electrode. In a further preferred embodiment, the iron disulfide particles are made using jet milling prior to being incorporated into the positive electrode.

Background of the invention

Lithium batteries (batteries containing metallic lithium as the active material of the negative electrode) are becoming increasingly popular as portable power sources, for electronic devices that have high power operating requirements. Lithium batteries for the common consumer include lithium / manganese dioxide (Li / MnO₂) and lithium / iron disulfide (Li / FeS₂), which have nominal voltages of 3.0 and 1.5 volts per cell, respectively.

Battery manufacturers are continually striving to design batteries with higher discharge capacity. This can be achieved by minimizing the volume of the stack occupied by the envelope, which includes the seal and the valve, thereby maximizing the internal volume available for the active materials. However, there will always be practical limitations on the maximum internal volume.

Another approach is to modify the internal design of the pile and the materials to increase the discharge capacity. How best to achieve this depends at least in part on the discharge requirements of the devices to be powered by batteries. For devices with low power requirements, the amount of active materials tends to be very important, while for devices with high power requirements, discharge efficiencies tend to be more important. Lithium batteries are often used in high-power devices, as they are capable of excellent discharge efficiencies at high-power discharges.

In general, the discharge efficiency of the battery decreases rapidly when the discharge power increases. So silly high discharge efficiency. This often means using designs that contain fewer active materials, thus sacrificing low-power, low-rate discharge capacity. For example, for good efficiency in high power discharges, a high interfacial surface between the negative electrode (anode) and the positive electrode (cathode) is desirable, relative to the volume of the electrodes. This is often accomplished using a spiral wound electrode assembly, in which relatively long, thin electrode bands are wound together on a coil. Unless the electrode compositions have high electrical conductivity, such long, thin electrodes typically require a current collector that extends over much of the length and width of the electrode band. The high interface surface of the electrodes also means that more spacer material is needed to electrically isolate the positive and negative electrodes from each other. Since maximum external dimensions for batteries are often set, either by industry standards, or by the size and shape of battery compartments in equipment, increasing the electrode interface also means having to reduce the amount of active electrode materials that can be used.

For batteries intended for both high- and low-power use, it is less desirable to reduce the input of active material from the cell to maximize high-power performance than for batteries intended for high-power use only. For example, Li / FeS batteries₂ (FR6 size) 1.5 volt AA size are intended for use in high power applications such as flash photography and digital still cameras, as well as general replacement for alkaline Zn / MnO batteries₂ 1.5 volt AA size, often used in low power devices. In such situations, it is important to maximize both the high power discharge efficiency and the input capacity of the cell. Although it is generally desirable to maximize the input capacity of the electrode in any cell, the relative importance of doing so is greater in cells for low power use.

To maximize the introduction of active materials into the cell, and consequently mitigate the effects of increasing the interface of the electrodes, it is desirable to use spacer materials that occupy the least possible internal volume in the cell. There are practical limitations to doing so. The separator must be able to withstand the cell manufacturing procedures without damage, provide adequate electrical insulation and ion transport between the anode and the cathode, and do so without developing defects that result in internal shorts between the anode and the cathode. when the battery is subjected to normal and abnormal conditions of handling, transport, storage and use.

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The properties of the spacer can be modified in various ways, to improve strength and resistance to damage. Examples are described in US Patent Nos. 5,952,120, 6,368,742, 5,667,911, and 6,602,593. However, changes made to increase strength may also adversely affect separator performance, based in part on factors such as cell chemistry, electrode design and characteristics, cell manufacturing process, and usage. intended for the battery, the intended conditions of storage and use, etc.

For certain battery chemistries, which maximize the amounts of active materials in the battery, it can be more difficult. In lithium batteries, in which the active material of the cathode reacts with the lithium to produce the reaction products, which have a total volume greater than that of the reactants, the swelling of the electrode assembly creates additional forces on the battery. These forces can cause the cell shell to bulge and shorts through the separator. Possible solutions to these problems include the use of strong (often thicker) materials for the cell envelope, and inert components within the cell, further limiting the internal volume available for the active materials in cells with such active materials, compared to stacks with lower volume reaction products. For Li / FeS batteries₂Another possible solution, described in US Patent No. 4,379,815, is to balance the expansion of the cathode and the contraction of the anode by mixing another active material with the FeS.₂. Such active cathode materials include CuO, Bi₂OR₃, Pb₂Bi₂OR₅, P₃OR₄, CoS₂, and their mixtures. However, adding other active materials to the cathode mix can affect the electrical and discharge characteristics of the cell.

As battery manufacturers are continually trying to improve discharge capacity, they are also continually working to improve other battery characteristics, such as safety and reliability; building batteries that are more resistant to internal short circuits can contribute to both. As is clear from the above discussion, changes made to improve internal short circuit resistance may be counterproductive to maximize discharge capacity.

Pyrite or iron disulfide (FeS₂) used in electrochemical cell cathodes are typically derived from natural mineral that is crushed, heat treated, and dry ground to a particle size of 20 to 30 microns (pm). The fineness of the grinding is limited by the reactivity of the particles with air and humidity. As the size of the particles is reduced, their surface increases, and is altered by atmospheric agents. Weathering is an oxidation process in which iron disulfide reacts with moisture and air to form iron sulfates. The alteration process by atmospheric agents results in an increase in acidity, and a reduction in electrochemical activity. Small pyrite particles can generate enough heat during oxidation to cause dangerous fires in the processing operation. The prior art iron disulfide particles used can have particle sizes approaching the final cathode coating thickness of about 80 microns, due to the non-uniformity of the dry milling process.

The iron disulfide dry milling process is typically carried out by a mining company or an intermediary, where large amounts of material are produced. Processed iron disulfide is generally transported and stored for long periods of time before being used by the battery industry. In this way, during the storage period, oxidation and alteration by the atmospheric agents mentioned above occur, and the material degrades. In addition, large iron disulfide particle sizes can have a strong effect in processes such as calendering, causing distortion of the substrate, breakage of the bond between the coating and the substrate, as well as failures from spacer damage.

Summary of the invention

In view of the above, an object of the present invention is to provide a lithium battery cell with increased discharge capacity. Another object of the invention is to provide a lithium battery cell with a high energy density (quotient between interfacial discharge capacity and interfacial electrode volume). Another object of the invention is to provide a Li / FeS2 cell with a high electrode interface, with an increase in discharge capacity in low-power discharges, without sacrificing discharge efficiency in high-power discharges, preferably one with an increase in discharge capacity in both high-rate and low-rate discharges. Yet another object of the invention is to provide a Li / FeS2 cell with increased cathode interfacial capacity and having both improved energy density and good resistance to internal short circuits.

A further object of the present invention is to provide an electrochemical cell with a positive electrode comprising FeS particles₂ relatively small average particle size. A further object is to provide an electrochemical cell with increased low and high rate product performance. Still another object is to provide an electrochemical cell that maintains a high output voltage for an extended period of time. Still a further object of the invention is to provide methods for preparing electrochemical cells, and especially a positive electrode, the method therefore including the steps of forming a suspension comprising FeS2 particles and a wetting agent; use a mill, particularly a media mill, to reduce the average particle size of the FeS2 particles, and subsequently form the positive electrode using the suspension. Another object of the present invention is to provide electrochemical cells with a positive electrode comprising iron disulfide particles that have been ground to a desired range of sizes.

ES 2 304 697 T3 particle media, using a process such as jet milling, in which substantially no heat is generated, and a narrow particle size distribution is obtained.

The above objects are met, and the above disadvantages of the prior art are overcome by the present invention, as taught in the claims.

Accordingly, one aspect of the present invention is directed to an electrochemical battery cell comprising an envelope; a negative electrode band comprising metallic lithium, a positive electrode band comprising a mixture of active material, and an electrolyte comprising at least one salt dissolved in a nonaqueous electrolyte disposed within the shell; and a separator arranged between the positive and negative electrodes; the cell having a ratio between the interfacial capacity of the cathode and the interfacial volume of the electrode assembly of at least 710 mAh / cm³.

Another aspect of the present invention is directed to an electrochemical battery cell comprising an envelope; a negative electrode, a positive electrode, and an electrolyte disposed within the shell; and a separator arranged between the negative and positive electrodes. The envelope comprises a cylindrical container with an integrated closed lower end, an initially open upper end, a side wall extending between the lower and upper ends, and a lid arranged at the upper end to close the stack; the negative electrode is in the form of a band with two opposing main surfaces and comprises metallic lithium; the positive electrode is in the form of a band with two opposing major surfaces and comprises a mixture of active material, the active material comprising more than 50 weight percent iron disulfide; the electrolyte comprises one or more salts dissolved in a non-aqueous organic solvent; the negative and positive electrodes, and the spacer, form a cylindrical assembly of spirally wound electrodes, with a radial outer surface disposed adjacent to an inner surface of the side wall of the container; the electrode assembly has an interfacial volume; the positive electrode has an interfacial capacity; the quotient between the interfacial capacity of the positive electrode and the interfacial volume of the electrode assembly is at least 710 mAh / cm³; and the separator is a microporous membrane comprising polyethylene, with a machine direction and a transverse direction, an average thickness of less than 22 pm, and a tensile stress of at least 9.81 N / cm (1, 0 kgf / cm), both in the machine direction and in the cross direction.

Another aspect of the present invention is directed to an electrochemical battery cell comprising an envelope; a negative electrode, a positive electrode, and an electrolyte disposed within the shell; and a separator arranged between the negative and positive electrodes. The cell is a cylindrical Li / FeS cell₂ FR6 type with a spiral wound electrode assembly, having an interfacial volume of the electrode assembly; the battery has an interfacial capacity of at least 3500 mAh; The separator is a microporous membrane comprising polyethylene and has an average thickness of less than 22 pm, a tensile stress of at least 19.6 N / cm (2.0 kgf / cm), both in the machine direction and in the cross direction, a dielectric breakdown voltage of at least 2400 volts, a maximum effective pore size of 0.08 pm to 0.20 pm, and a BET specific surface area of ​​4.0 to 15 m²/ g.

Still another aspect of the present invention is directed to an electrochemical battery cell comprising an envelope; a negative electrode, a positive electrode, and an electrolyte disposed within the shell; and a separator arranged between the negative and positive electrodes. The cell is a FR6 type Li / FeS2 cylindrical cell with a spiral wound electrode assembly having an interfacial volume of the electrode assembly; the separator is a microporous membrane comprising polyethylene and has an average thickness of less than 22 µm; a tensile stress of at least 19.6 N / cm (2.0 kgf / cm), both in the machine direction and in the transverse direction, a dielectric breakdown voltage of at least 2400 volts, and a size of maximum effective pore from 0.08 pm to 0.20 pm; the positive electrode comprises an active material comprising at least 95 weight percent iron disulfide; and the battery is capable of providing a discharge capacity of at least 2950 mAh when continuously discharging at 200 mA up to 1.0 volts, and a discharge capacity of at least 2600 mAh when continuously discharging at 1000 mA up to 1.0 volts.

A further aspect of the invention is directed to an electrochemical battery cell comprising an envelope; a negative electrode comprising lithium; a positive electrode comprising an active material, said active material comprising more than 49 weight percent iron disulfide, said iron disulfide having a mean particle size of from about 1 to about 19 pm; an electrolyte mixture comprising at least one salt dissolved in a non-aqueous electrolyte, disposed within the shell; and a separator arranged between the negative electrode and the positive electrode.

Still another aspect of the invention is directed to an electrochemical battery cell comprising an envelope; a negative electrode comprising lithium; a positive electrode comprising an active material, said active material comprising more than 49 weight percent iron disulfide; an electrolyte mixture comprising at least one salt dissolved in a non-aqueous electrolyte, disposed within the shell; and a spacer arranged between the negative electrode and the positive electrode, wherein (a) the electrolyte has a conductivity greater than 2.5 mS / cm and the spacer has a thickness of 1 to 25 pm; or (b) the electrolyte has a conductivity greater than 2.5 mS / cm, and the iron disulfide has a mean particle size of 1 to 19 pm; or (c) the separator has a thickness of 1 to 25 pm and the iron disulfide has an average particle size of 1 to 19 pm.

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Still another aspect of the invention is directed to a process for preparing a cathode, comprising the steps of forming a suspension comprising a wetting agent and iron disulfide particles with a mean particle size greater than 20 pm, grinding the suspension using a media mill comprising grinding media, to reduce the particle size of the iron disulfide particles to an average particle size of 1 to 19 μιη, applying the ground cathode suspension to a cathode substrate to form a cathode, and drying the cathode.

Still another aspect of the invention is directed to an electrochemical battery cell comprising an envelope; a negative electrode comprising lithium; a positive electrode comprising an active material, said active material comprising more than 49 weight percent iron disulfide; an electrolyte mixture comprising at least one salt dissolved in a non-aqueous electrolyte, disposed within the shell; and a separator arranged between the negative electrode and the positive electrode, in which the battery is a FR6 type battery that has a discharge time of at least 320 minutes to 1.05 volts, according to a test for digital cameras "Digital Still Camera ”(DSC) at 1500/650 mW 2/28 s X 10 per hour at room temperature.

These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art, by reference to the following specification, claims, and accompanying drawings.

Unless otherwise specified, as used in the present invention, the expressions below are defined as follows:

• Active material - one or more chemical compounds that are part of a cell's discharge reaction and contribute to the cell's discharge capacity, including impurities and small amounts of other debris present;

• Active material mixture - a mixture of solid electrode materials, excluding current collectors and electrode conductors, containing the active electrode material;

• Mean particle size - the mean diameter of the volume distribution of a sample of a composition (MV); can be determined using a Microtac Honeywell Model X-100 Particle Size Analyzer, equipped with a Model 9320 Large Volume Recirculator (LVR) (4L volume). The measurement method uses ultrasound to break up the agglomerates and prevent them from turning back. to form agglomerates. A sample of approximately 2.0 grams is weighed and placed in a 50 ml beaker. 20 ml of deionized water and 2 drops of surfactant (a 1% Ot aerosol solution prepared from 10 ml of 10% OT aerosol available from Fisher Scientific, in 100 ml of deionized water by mixing the solution well). The sample solution in the beaker is stirred, preferably with a stir bar. The large volume recirculator is filled to level with deionized water, and the sample is transferred from the beaker to the recirculator vessel. A wash bottle is used to rinse any sample particles that remain inside the recirculator container. The sample is allowed to recirculate for one minute before starting measurements. The following parameters are entered for the FeS particles₂: Transparent Particles - No (absorbing); Spherical Particles - No; Fluid Refractive Index - 1.33; Run time - 60 seconds;

• Capacity, discharge - the actual capacity obtained from a battery during discharge, generally expressed in ampere-hours (Ah) or milliamp-hours (mAh);

• Capacity, entered - the theoretical capacity of an electrode, equal to the weight of each active material on the electrode times the theoretical specific capacity of that active material, where the theoretical specific capacity of each active material is determined according to the following calculation:

[(96,487 ampere-seconds / mol) / (number of grams / mol of active material)] x (number of electrons / mol of active material) / (3600 seconds / hour) x (1000 milliamp-hours / ampere-hours) (for example, Li = 3862.0 mAh / g, S = 1672.0 mAh / g, FeS₂ = 893.6 mAh / g, CoS₂ - 871.3 mAh / g, CF_X = 864.3 mAh / g, CuO = 673.8 mAh / g, C2F = 623.0 mAh / g, FeS = 609.8 mAh / g, CuS = 560.7 mAh / g, Bi₂OR₃ = 345.1 mAh / g, MnO₂ = 308.3 mAh / g, Pb₂Bi₂OR₅ = 293.8 mAh / g and FeCuS₂ = 292.1 mAh / g);

• Capacity, interfacial of the cell - the smaller of the capacities of the negative and positive electrodes;

• Capacity, interfacial of the electrode - the total contribution of an electrode to the theoretical discharge capacity of the cell, based on the overall discharge reaction mechanism (s) of the cell and the total amount of active material contained within the cell. part of the active material mixture adjacent to the active material of the opposite electrode, assuming a complete reaction of all the active material, generally expressed in Ah or mAh (where only one of the two main surfaces of an electrode strip is adjacent to the active material of the opposite electrode, only the active material on that face of the electrode - or the material on that face of a sheet of a solid current collector or the material half the thickness of an electrode without a foil of a solid current collector - is included in the determination of the interfacial capacity);

ES 2 304 697 T3 • Electrode assembly - the combination of the negative electrode, positive electrode, and spacer, as well as any insulating material, overwrap, tape, etc., that is incorporated, but excluding any different electrical conductors added to the active material, active material mixture, or current collector;

• Electrode gap - the distance between adjacent positive and negative electrodes;

• Electrode charge - dry weight of active material mixture per unit surface area of ​​the electrode, generally expressed in grams per square centimeter (g / cm²);

• Packing of the electrodes - dry weight of active material per unit area of ​​the electrode, divided by the dry weight of the theoretical active material mixture per unit area of ​​the electrode, based on the actual densities of the solid materials in the mixture, expressed generally as a percentage;

• Bent electrodes - bands of electrodes that are combined in an assembly by bending, with the lengths of the bands either parallel or crossing one another;

• Interfacial height, of the electrode assembly - the average height, parallel to the longitudinal axis of the stack, of the interface of the electrodes in the assembly;

• Interfacial volume, of the electrode assembly - the volume within the cell envelope, defined by the transverse surface, perpendicular to the longitudinal axis of the cell, on the inner surface of the lateral wall (s) ) of the vessel and the interfacial height of the electrode assembly;

• Nominal - a value, specified by the manufacturer, that is representative of what can be expected for that characteristic or property;

• Percent discharge - the percentage of the estimated capacity drawn from a battery during discharge;

• Ambient temperature - between approximately 20 ° C and approximately 25 ° C;

• Spiral wound electrodes - bands of electrodes that are combined into an assembly by wrapping along their lengths or widths, for example around a central core or mandrel; and • Void volume of the electrode assembly - the volume of the void spaces of the electrode assembly per unit of interfacial height, determined by subtracting the sum of the volumes of the non-porous components of the electrode assembly and the solid parts of the electrode assembly. the porous components of the electrode assembly contained within the interfacial height, to the interfacial volume of the electrode assembly (microporous spacers, insulating films, tapes, etc., are non-porous and incompressible, and the volume of a porous electrode is determined using the actual densities of the components and the actual total volume), generally expressed in cm³/ cm.

Brief description of the drawings

The invention will be better understood, and other features and advantages will be apparent from reading the detailed description of the invention, in conjunction with the drawings, in which:

Figure 1 is an embodiment of the battery electrochemistry of the invention;

Figure 2 is a graph showing the results of the impact test on partially discharged FR6 cells, as a function of the volume of voids per unit height of the electrode mounting within the interfacial height;

Figure 3a illustrates a photomicrograph obtained by scanning electron microscopy (SEM), with a magnification of 1,000 times, of a part of a positive electrode containing FeS particles.₂ of the prior art;

Figure 3b illustrates a photomicrograph obtained by scanning electron microscopy (SEM), with a magnification of 1,000 times, of a part of a positive electrode containing FeS particles.₂ produced using the media mill milling process of the invention;

Figure 4 is a representation of the cathode efficiency in a “Digital Still Camera” (DSC) application, as a function of the thickness of the separator, for groups of FR6-type batteries built with different separator thicknesses, mean particle size of FeS2, and electrolyte composition;

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Figure 5 is a graph of the anode voltage as a function of the percent depth of discharge of an electrochemical cell containing FeS.₂ of the prior art, from a cell containing FeS particles₂ milled media, and from a pile containing FeS particles₂ jet ground; Y

Figure 6 is a graph of cell voltage as a function of percent discharge depth of a prior art electrochemical cell containing FeS2, of a cell containing media-milled FeS2 particles, and of a pile containing jet milled FeS2 particles.

Description of the invention

The battery cell of the invention has an anode comprising metallic lithium as the active material of the negative electrode. Both the anode and cathode are in the form of bands, which are joined in an electrode assembly to provide a high interfacial surface, relative to the volumes of the electrodes containing active material. The larger the interfacial surface, the lower the current density, and the better the battery's ability to deliver high power in discharge. The cell also has a high ratio between the interfacial capacity of the cathode and the interfacial volume of the electrode assembly - at least 710 mAh / cm². This means that the volume of active materials in the electrode assembly is high, to provide a high discharge capacity. The high volume of active materials can be achieved by controlling several variables, including: the ratio of the interfacial input capacity to the total input capacity, the volume of the cathode current collector, the concentration of the cathode active material in the cathode mixture , and the volume of the separator in the electrode assembly.

The invention will be better understood with reference to Figure 1, which shows an embodiment of a battery according to the invention. Cell 10 is a cylindrical Li / FeS battery cell₂ FR6 type. Stack 10 has an envelope that includes a container 12 with a closed bottom and one of stack 14, and a gasket 16. Container 12 has a reduced diameter rim or stage near the upper end to support gasket 16 and cap 14. Gasket 16 is compressed between container 12 and cap 14 to seal an anode 18, cathode 20, and electrolyte within cell 10. Anode 18, cathode 20, and a spacer 26 are spirally wound together in an electrode assembly. Cathode 20 has a metallic current collector 22, which extends from the upper end of the electrode assembly, and is connected to the inner surface of cap 14 with a contact spring 24. Anode 18 is electrically connected to the inner surface of container 12 by means of a tab (not shown). An insulating cone 46 is positioned around the peripheral portion of the top of the electrode assembly to prevent the cathode 22 current collector from contacting the container 12, and contact between the bottom edge of the cathode 20 and the bottom. Container 12 is prevented by the inwardly folded extension of spacer 26 and an electrically insulating lower disk 44, positioned at the bottom of container 12. Stack 10 has a separate positive terminal cap 40, which is held in place by the inwardly folded top edge of container 12 and gasket 16. Container 12 serves as a negative contact terminal. Disposed between the peripheral rim of the terminal cap 40 and the battery cap 14 is a positive temperature coefficient (PTC) device 42, which substantially limits current flow under abusive electrical conditions. Stack 10 also includes a pressure relief valve. The cell cover 14 has an opening comprising an inwardly projecting central purge cavity 28, with a purge port 30 at the bottom of cavity 28. The opening is sealed by a purge ball 32 and a thin-walled thermoplastic sleeve 34, which is compressed between the vertical wall of the purge cavity 28 and the periphery of the purge ball 32. When the internal pressure of the cell exceeds a predetermined level, the purge ball, or both the ball 32 and the sleeve 34, are pushed out of the opening to release the pressurized gases from the cell 10.

The stack container is often a metal container with an integrated closed bottom; although, instead of a container, a metal tube that is initially open at both ends can also be used. The container is generally made of steel, nickel plated on at least the outer part to protect the outer part of the container from corrosion. The type of laminate can be varied to provide varying degrees of corrosion resistance, or to provide the desired appearance. The type of steel will depend in part on the way the container is formed. For deep-drawn containers, the steel can be a diffusion-annealed, low-carbon steel, quenched with aluminum, according to SAE 1006 standard or equivalent steel, with a grain size according to ASTM standard of 9 to 11, and with equiaxed grain shapes to slightly elongated. Other steels, such as stainless steels, can be used to meet special needs. For example, when the container is in electrical contact with the cathode, a stainless steel can be used for an improvement in resistance to corrosion by the cathode and the electrolyte.

The battery cover is typically metal. Nickel plated steel can be used, but stainless steel is often desirable, especially when the cap is in electrical contact with the cathode. The complexity of the shape of the cap will also be a factor in the selection of the material. The battery cover can have a simple shape, such as a thick, flat disk, or it can have a more complex shape, such as the cover shown in Figure 1. When the cap has a complex shape as in Figure 1, a Type 304 soft annealed stainless steel, grain size per ASTM 8-9, can be used to provide the desired corrosion resistance and ease of shaping the cap. metal. The shaped caps can also be laminated, for example nickel plated.

The terminal cover should have good resistance to corrosion from ambient water, good electrical conductivity, and, when visible on consumer batteries, an attractive appearance. Terminal caps are often manufactured from nickel plated cold rolled steel, or nickel plated steel after forming

ES 2 304 697 T3 covers. When the terminals are located on pressure-relieving valves, the terminal caps generally have one or more holes to facilitate purging of the cell.

The gasket is manufactured from any suitable thermoplastic material that provides the desired sealing properties. Material selection is based in part on the composition of the electrolyte. Examples of suitable materials include polypropylene, poly (phenylene sulfide), tetrafluoro-perfluoroalkyl vinyl ether copolymer, poly (butylene terephthalate), and combinations thereof. Preferred gasket materials include polypropylene (eg PRO-FAX® 6524 from Basell Polyolefins, Wilmington, DE, USA), polybutylene terephthalate (eg CELANEX® PBT, 1600A grade from Ticona-US, Summit , NJ, USA), and poly (phenylene sulfide) (eg TECHTRON® PPS from Boedeker Plastics, Inc., Shiner, TX, USA). Small amounts of other polymers, inorganic reinforcing fillers and / or organic compounds can be added to the gasket base resin.

The joint can be coated with a sealing material to provide the best seal. Ethylenepropylene-diene terpolymer (EPDM) is a suitable sealing material, but other suitable materials can be used.

The purge sleeve is made from a thermoplastic material that is resistant to cold flow at high temperatures (eg 75 ° C). The thermoplastic material comprises a base resin such as ethylene-tetrafluoroethylene, poly (butylene terephthalate), poly (phenylene sulfide), polyphthalamide, ethylene-chloro-trifluoroethylene, chlorotrifluoroethylene, perfluoroalkoxyalkane, perfluoroethylene-fluorinated polypropylene, and fluorinated poly (ether-polypropylene). ketone). Ethylene-tetrafluoroethylene copolymer (ETFE), poly (phenylene sulfide) (PPS), poly (butylene terephthalate) (PBT), and polyphthalamide are preferred. The resin can be modified by adding a thermal stabilizing filler, to provide a purge sleeve with the desired sealing and purging characteristics at high temperatures. The sleeve can be injection molded from the thermoplastic material. TEFZEL® HT2004 (ETFE resin with 25 weight percent cut glass filler) is a preferred thermoplastic material.

The purge ball can be manufactured from any suitable material that is stable in contact with the contents of the cell, and provides the desired sealing and purging characteristics of the cell. Glasses or metals can be used, such as stainless steel.

The anode comprises a band of metallic lithium, sometimes referred to as a lithium foil. The composition of lithium can vary, although for battery grade lithium the purity is always high. Lithium can be alloyed with other metals, such as aluminum, to provide the desired electrical performance of the cell. A battery grade lithium-aluminum foil containing 0.5 weight percent aluminum is available from Chemetall Foote Corp., Kings Mountain, NC, USA.

The anode may have a current collector, within or on the surface of the metallic lithium. As in the battery in Figure 1, a different current collector may not be necessary, as lithium has a high electrical conductivity, but a current collector may be included, for example, to maintain electrical continuity within the anode during charging. discharge, as lithium is consumed. When the anode includes a current collector, it can be made of copper due to its conductivity, but other conductive metals can be used as long as they are stable within the cell.

A thin metal band often serves as an electrical conductor, or tab, that connects the anode to one of the battery terminals (the packaging in the case of the FR6 battery shown in Figure 1). The metal band is often made from nickel or nickel-plated steel, and glued directly to lithium. This can be accomplished by embedding one end of the conductor within a portion of the anode, or simply pressing one end of the conductor onto the surface of the lithium foil.

The cathode is in the form of a band comprising a current collector and a mixture that includes one or more electrochemically active materials, usually in particulate form. Iron disulfide (FeS₂) is a preferred active material. In a Li / FeS stack₂, the active material comprises more than 50 weight percent FeS₂. The cathode may also contain one or more additional active materials, depending on the desired electrical and discharge characteristics of the cell. The additional cathode active material can be any suitable cathode active material. Examples include Bi₂OR₃, C₂F, CF_x, (CF)_n, CoS₂, CuO, CuS, FeS, FeCuS₂, MnO₂, Pb₂Bi₂OR₅, and S. More preferably, the active material for a Li / FeS cell cathode₂ it comprises at least 95 weight percent FeS2, still more preferably at least 99 weight percent FeS2, and most preferably FeS2 is the only active material on the cathode. The FeS₂ grade of battery, having a purity of at least 95 percent by weight, is available from American Minerals, Inc., Camden, NJ, USA; Chemetall GmbH, Vienna, Austria; Washington Mills, North Grafton, MA; and Kyanite Mining Corp., Dillwyn, VA, USA.

In addition to the active material, the cathode mixture contains other materials. A binder is generally used to hold the particulate materials together, and adhere the mixture to the current collector. One or more conductive materials such as metal, graphite, and powdered carbon black can be added to provide an increase in electrical conductivity to the mixture. The amount of active material used may depend on factors such as the electrical conductivity of the active material and binder, the thickness of the mixture on the current collector, and the design of the current collector. Small amounts of various additives can also be used to improve cathode fabrication and cell performance. The following are examples of materials for the active material mixture for Li / FeS cell cathodes₂. Graphite: synthetic graphite grades KS-6 and TIMREX® MX15, from Timcal

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America, Westlake, OH, USA Carbon Black: C55 grade acetylene black, from Chevron Phillips Company LP, Houston, TX, USA Binder: Ethylene-Propylene Copolymer (PEPP), manufactured by Polymont Plastics Corp. (formerly Polysar, Inc.), and available from Harwick Standard Distribution Corp., Akron, OH, USA; water-soluble nonionic polyethylene oxide (PEO): POLYOX® from Dow Chemical Company, Midland, MI, USA; and G1651 grade styrene-ethylene / butylene-styrene block copolymer (SEBS) from Kraton Polymers, Houston, TX. Additives: FLUO HT®, micronized polytetrafluoroethylene (PTFE), manufactured by Micro Powders Inc., Tarrytown, NY, USA. (commercially available from Dar-Tech Inc., Cleveland, OH, USA), AeROSIL® 200 grade fumed silica, from Degussa Corporation Pigment Group, Ridgefield, NJ.

The current collector may be disposed within, or embedded in, the cathode surface, or the cathode mixture may coat one or both faces of a thin metal band. Aluminum is a commonly used material. The current collector may extend beyond the part of the cathode that contains the cathode mixture. This portion of the current collector that is extended can provide a useful surface for making contact with the electrical conductor connected to the positive terminal. It is desirable to keep the volume of the extending portion of the current collector to a minimum, to achieve the maximum internal cell volume available for the active materials and electrolyte.

A preferred method of making FeS cathodes₂ is roll coating a suspension of active material mixture materials in a highly volatile organic solvent (e.g. trichlorethylene) on both sides of an aluminum foil sheet, drying the coating to remove the solvent, calendering the coated sheet to compact the coating, strip the coated sheet to the desired width, and strip the cut cathode material to the desired length. It is desirable to use small particle size cathode materials to minimize the risk of puncturing the separator. For example, FeS2 is preferably screened through a 230 mesh (63 pm) screen prior to use.

In a further embodiment, a positive cathode or electrode is disclosed that provides beneficial properties to an electrochemical cell incorporating it. The cathode comprises FeS particles₂ having a predetermined average particle size, prepared by a wet milling method, such as a media mill, or a dry milling method using a non-mechanical milling device, such as a jet mill. Electrochemical cells prepared with the reduced mean particle size FeS2 particles show an increase in cell voltage at any given depth of discharge, regardless of cell size.

In one embodiment of the present invention, the cathode comprises FeS particles₂ of small particle size, preferably natural, prepared by a wet milling method, preferably using a media mill. Reference has also been made in the art to a media mill such as a ball mill, basket mill, pearl mill, sand mill, rotary drum mixer, or the like, which may use milling media in a grinding process in damp. The wet milling step is preferably carried out in-line during the construction of the cathode or positive electrode, thereby substantially eliminating weathering or oxidation, as well as dry powder pyrite fires. By using the wet milling process of the present invention, the above-mentioned sieving operation can be eliminated.

In the wet milling method, a mixture of electrochemically active cathode material is formed, comprising the FeS2 and a wetting agent. At this point in the procedure, FeS2 has a mean particle size greater than 20 pm. Any of the active or inactive materials described above, such as, but not limited to, binders, conductive material, additives, etc., can also be used in the active material mixture, if desired. In one embodiment, the components of the cathode active material mixture are combined, and optionally, but preferably, mixed in a suitable container. The cathode active material mixture is measured inside the media mill, where the average particle size of the FeS2 particles is reduced during milling. The residence time of the cathode active material mixture within the media mill is sufficient to produce the desired range of average FeS particle sizes.₂.

The wetting agent is any liquid or the like, preferably of low viscosity, which substantially prevents the FeS2 or the other components of the suspension from burning during the milling process. The preferred wetting agent is a solvent that is generally non-flammable under the processing conditions used during the wet milling operation. Examples of suitable wetting agents include, but are not limited to, trichlorethylene, N-methyl-2-pyrrolidone (NMP), butylglycol acetate, mineral spirits, and water. The wetting agent is selected to be at least compatible with, and preferably capable of dissolving, the binder used in the preparation of the cathode. The amount of wetting agent can vary, and can generally be in a range from about 0.1 cm³ up to about 5 cm³, and is preferably 0.5 cm³ per gram of solid components of the cathode active material mixture.

The active material suspension mixture from the cathode is transferred to a grinding device, and ground at an appropriate flow rate and rotor rpm, until the average FeS particle size is achieved.₂ wanted. A media mill is used in a preferred embodiment. Media mills typically comprise shaft-mounted rotating discs and / or rotors, as well as grinding means to reduce the particle size of the composition components to be ground. The grinding media can be substantially spherical, cylindrical, or the like, with spheres being preferred, with mean diameters ranging from about 0.2 mm to approx.

ES 2 304 697 T3 approximately 30 mm, and desirably from about 0.5 to about 10 mm, and preferably from about 1.2 to about 1.7 mm. The height of the cylinders ranges from about 1mm to about 20mm, with about 5 to about 15mm being preferred. Numerous types of media can be used and include, but are not limited to, calcium soda, zirconiosilicate dioxide, aluminum oxide, yttrium oxide stabilized zirconium dioxide-silica, chromium steel, zirconium silicate, zirconium dioxide stabilized with cerium, yttrium oxide stabilized zirconium dioxide, and tungsten carbide. Suitable grinding media are available from suppliers such as Saint-Gobain of Worcester, MA such as Glass, ER120, Zirstar, and Zirmil; Glenn Mill of Cliffton, NJ as Alumina, Steel, and Carbide; and Jyoti Ceramic Industries of Satpur, Nashik, India as Zirconox and Zircosil. A suitable media mill is available from Morehouse-COWLES of Fullerton, California.

The active material suspension mixture from the cathode is transferred to the media mill's grinding chamber, which contains grinding media, and preferably shaft-mounted rotors that can rotate. The media is accelerated at a relatively high speed, through the suspension towards the wall of the grinding chamber, impacting, shearing, and thereby reducing the particle size of the suspension mixture. The ground slurry mixture is subsequently discharged from the media mill for further processing at a cathode, after a desired mean particle size of FeS2 particles has been achieved.

After processing using the wet milling method of the invention, the FeS2 particles have a mean particle size of from about 1 to about 19 pm, desirably from about 2 to about 17 or about 18 pm, and preferably from about 5 or about 10 until about 15 pm. FeS particles₂ they also have a narrower particle size distribution, due to the media milling process performed.

Subsequently, a sheet is roll coated with the wet milled cathode active material mixture, such as aluminum foil, as described above, and dried to remove the wetting agent. The laminated material of the coated sheet can then be calendered to compact the coating, and prepare a smooth surface, and the coated sheet can be cut into strips to a desired width and length, for use in mounting an electrochemical cell, as described. in the present invention.

In a further embodiment of the present invention, the cathode comprises FeS2 particles, preferably natural, of a predetermined mean particle size range, obtained by a non-mechanical grinding device, preferably a jet mill. The term "non-mechanical grinding device" refers to an apparatus that does not use pressure or contact between two or more surfaces of a mill to reduce the particle size of a material such as by grinding, chopping, fracturing, or the like. Devices for mechanical grinding include, but are not limited to, roll mills, granulating mills, ball mills, media mills, pearl mills, and hammer mills. Non-mechanical grinding devices typically reduce the mean particle size of FeS2 particles without using moving grinding parts, and instead reduce the size using collisions between particles and / or particles and a single surface of the grinding device.

A jet mill typically includes a central chamber into which a fluid such as air, steam, or gas is introduced, through nozzles or jets, that create a stream of grind near the speed of sound, at the speed of sound, or supersonic. Grinding media are not used. The feedstock particles comprising FeS2 particles feed or are injected into the high speed grind stream of the jet mill. The size reduction occurs due to high speed collisions between iron disulfide particles or other particles with each other, or collision with a mill surface. Jet mills are designed to allow the recirculation of oversized particles, improving the frequency and effect of particle collisions. As the FeS2 particles are reduced in size, they migrate to a discharge port from which they are collected for use in an active material mixture used to form a cathode. In a preferred embodiment, the jet milling of the FeS2 is carried out in an inert atmosphere using a gas such as nitrogen, argon, or the like, with nitrogen being more preferred, to prevent ignition or combustion of the FeS2 particles. Although heat can be generated by the friction of the FeS2 particles rubbing on the surfaces of the mill and from collisions that take place in the mill, due at least to the Jewel-Thompson effect in the temperature of the air when the throttling occurs, according to there is reportedly no net increase in temperature during milling. The temperature of the product is substantially equal to the temperature of the fluid supplied to the mill. Jet mills are available from the Jet Pulverizer Company of Moorestown, NJ; Sturtevant of Hanover, MA; as well as Fluid Energy of Telford, PA.

After processing using the non-mechanical or jet milling method of the invention, the FeS particles₂ they have an average particle size of from about 1 to about 19 pm, desirably from about 1.5 to about 10 or about 15 pm, and preferably from about 2 to about 6 pm. FeS particles₂ Jet milled have a particle size distribution where 80% of the total particles are between about 1.0 and about 15 pm, and preferably between about 1.0 and about 10 pm. The particle size distribution was determined using the Microtac Honeywell model X-100 particle size analyzer described above in the present invention, in which exposure to ultrasound during the assay is used to prevent aggregation of the particles.

ES 2 304 697 T3

The grinding processes of the present invention, used to reduce the mean particle size of FeS particles, have been shown to₂ within the ranges stated in the present invention, they offer several advantages including, for example, improved low temperature battery performance, improved adhesion of the active material mixture from the cathode to the aluminum substrate, less damage to the insulating film of polymeric separator due to the small particle sizes of the active material mixture, an improvement in the efficiency of the cathode as a result of more pyrite particles with an increase in the surface area, to accept lithium ions after the battery is discharged, an increase in the operating voltage of the battery due to the decrease in the polarization of the anode, allowing batteries to run at lower currents in constant power device applications, and more efficient and uniform discharge at the opposite lithium anode, since the current distribution can be applied more evenly over its interface surface.

FR6 type electrochemical cells prepared using wet ground FeS2 particles or jet ground FeS2 particles are capable of providing a discharge capacity of at least 3,000 milliamp hours (mAh), when continuously discharged at a rate of 200 mA up to one volt, as well as at least 2,700 mAh, or preferably at least 2,800 mAh when continuously discharged at a rate of 1 A to one volt, at room temperature. Accordingly, the cells of the present invention provide excellent results for both low- and high-rate applications.

It has also been found that FR6 electrochemical cells using FeS particles₂ jet milled as described herein, have a discharge time of generally at least 300 minutes, desirably at least 320 minutes, preferably at least 325 minutes, and most preferably at least 330 or 340 minutes up to 1.05 volts, as tested by DSC at 1500/650 mW 2/28 sx 10 per hour. FR6 type electrochemical cells comprising jet milled FeS2 particles with a mean particle size within the range specified in the invention have also been found to maintain a voltage> 1.2 for at least 180 minutes, desirably at least 240 minutes, and preferably at least 270 minutes, according to the DSC test at 1500/650 mW 2/28 sx 10 per hour. The DSC procedure cycles the electrochemical cell using two pulses, the first pulse at 1500 mW for 2 seconds, followed by the second pulse at 650 mW for 28 seconds. The pulse sequence is repeated 10 times, followed by a 55 minute rest period. Thereafter, the pulse sequence and the rest period are repeated up to a predetermined voltage. Furthermore, FR6-type electrochemical cells comprising wet-ground FeS2 particles have been found to maintain a voltage> 1.2 for at least 180 minutes, desirably at least 210 minutes, and preferably at least 230 minutes, as tested. DSC at 1500/650 mW 2/28 sx 10 per hour. FR6 type electrochemical cells using wet ground FeS2 particles have a discharge time of at least 300 minutes, and preferably at least 320 minutes to 1.05 volts, according to the DSC test at 1500/650 mW 2 / 28 sx 10 per hour. Measurements were carried out at room temperature.

FR6 electrochemical cells prepared using relatively small average particle size FeS2 particles, which are obtained from the grinding methods of the present invention, such as wet or jet grinding, provide reduced anode stress values ​​at various times. percent depth of discharge, when compared to prior art cells containing FeS2 particles with a mean size greater than or equal to about 22 microns, as illustrated in Figure 5. At 50% depth of discharge, the anode voltage for an electrochemical cell which has FeS particles₂ Average particle size within the ranges of the present invention is less than 190 millivolts, desirably less than 170 millivolts, preferably less than 100 millivolts, and most preferably less than about 60 millivolts. At 25% depth of discharge, the anode voltage is less than 140 millivolts, desirably less than 120 millivolts, and preferably less than 75 millivolts. To obtain the measurements, the stacks were discharged using a Solartron 1470, available from Solatron Analytical, Farnborough, England. The current was chosen such that the current density was approximately 5 mA / cm². The batteries were cycled for 2 minutes at 1 A, and 5 minutes at 0 A. The batteries were referenced by removing the bottom of the package from the battery, and suspending the battery in a beaker containing electrolyte, in this case, 0, 75 moles per liter of solvent (9.1% by weight) of lithium iodide, in a solvent mixture of 1,3-dioxolane, 1,2-diethoxyethane, and 3,5-dimethylisoxazole (63.1: 27, 6: 0.20% by weight). The reference electrode, which is a pure metal lithium band on the barrel of a syringe with a Vycor end, is located opposite the battery side. The system is allowed to equilibrate for approximately 30 minutes prior to flushing. Measurements were carried out at room temperature.

The cathode is electrically connected to the positive terminal of the battery. This can be accomplished with an electrical conductor, often in the form of a thin metal band or spring, as shown in Figure 1. The conductor is often made of nickel-plated stainless steel.

The separator is a thin microporous membrane that is permeable to ions, and electrically insulating. It is capable of keeping at least some electrolyte within the pores of the separator. The separator is disposed between adjacent surfaces of the anode and the cathode, to electrically isolate the electrodes from each other. Parts of the separator can also isolate other components in electrical contact with the battery terminals, to prevent internal short circuits. The edges of the spacer often extend beyond the edges of at least one electrode, to ensure that the anode and cathode do not make electrical contact, even if they are not perfectly aligned with each other. However, it is desirable to minimize the amount of spacer that extends beyond the electrodes.

ES 2 304 697 T3

To provide good discharge performance at high power, it is desirable that the separator have the characteristics (pores with the smallest dimension of at least 0.005 pm, and the largest dimension of not more than 5 pm through, a porosity in the range from 30 to 70 percent, a specific surface resistance from 2 to 15 O.cm², and a tortuosity of less than 2.5) described in US Patent No. 5,290,414, issued March 1, 1994, and incorporated herein by reference. Suitable separator materials must also be strong enough to withstand the cell manufacturing procedures, as well as the pressure that can be exerted on the separator during discharge from the pile, without tears, slits, holes, or other openings to be seen. develop, which may result in an internal short circuit.

To minimize the total volume of the separator in the stack, the separator should be as thin as possible, but at least about 1 pm or more, such that a physical barrier is present between the cathode and the anode to prevent short circuits. internal That said, the thickness of the spacer ranges from about 1 to about 50 pm, desirably from about 5 to about 25 pm, and preferably from about 10 to about 16 or about 20 pm. The thickness required will depend in part on the strength of the spacer material, and the magnitude and location of the forces that can be exerted on the spacer where it provides electrical insulation.

In addition to thickness, several characteristics can affect the strength of the separator. One of these is tensile stress. High tensile stress is desirable, preferably at least 7846 N / cm² (800 kgf / cm²), more preferably at least 9807 N / cm² (1000 kg of force per square centimeter (kgf / cm²)). Due to the manufacturing processes typically used to make microporous spacers, the tensile stress is typically higher in the machine direction (MD) than in the transverse direction (TD). The minimum tensile stress required may depend in part on the diameter of the pile. For example, for a FR6 type pile, the preferred tensile stress is at least 14710 N / cm² (1500 kgf / cm²) in the machine direction, and at least 11768 N / cm² (1200 kgf / cm²) in the transverse direction, and for a FR03 type pile, the preferred tensile strengths are at least 12749 and 9807 N / cm² (1300 and 1000 kgf / cm²), respectively. If the tensile stress is too low, the build and internal forces in the stack can cause tears or other holes. In general, the higher the tensile stress, the better from a strength point of view. However, if the tensile stress is too high, other desirable properties of the spacer may be impaired.

The tensile stress can also be expressed in N / cm (kgf / cm), which can be calculated from the tensile stress in N / cm² (kgf / cm²), multiplying the last one by the thickness of the separator in cm. Tensile stress in N / cm (kgf / cm) is also useful for identifying desirable properties related to separator strength. Therefore, it is desirable that the spacer have a tensile stress of at least 9.8 N / cm (1.0 kgf / cm), preferably at least 14.7 N / cm (1.5 kgf / cm). , and more preferably at least 17.2 N / cm (1.75 kgf / cm), both in the machine direction and in the transverse direction. For piles with diameters greater than about 11.4 mm (0.45 inches), a tensile stress of at least 19.6 N / cm (2.0 kgf / cm) is most preferable.

Another indicator of the strength of the separator is its dielectric breakdown voltage. Preferably, the average dielectric breakdown voltage will be at least 2000 volts, more preferably at least 2200 volts. For cylindrical cells with a diameter greater than about 11.4 mm (0.45 inches), the average dielectric breakdown voltage is most preferably at least 2400 volts. If the dielectric breakdown voltage is too low, it is difficult to reliably remove batteries with faulty or damaged spacers by electrical testing (e.g. retention of a high voltage applied to the electrode mounting prior to electrolyte addition) during manufacture from the stack. It is desirable that the dielectric breakdown be as high as possible while still achieving other desirable properties of the separator.

Mean effective pore size is another of the most important indicators of separator strength. Although large pores are desirable to maximize ion transport through the separator, if the pores are too large the separator will be prone to penetration and shorts between the electrodes. The preferred maximum effective pore size is from 0.08 pm to 0.40 pm, more preferably not greater than 0.20 pm.

The specific surface is also related to the pore size, as well as the number of pores. In general, the discharge performance of the cell tends to be better when the separator has a larger specific surface area, but the resistance of the separator tends to be lower. It is desirable that the BET specific surface is not greater than 40 m²/ g, but it is also desirable that it be at least 15 m²/ g, more preferably at least 25 µm²/ g.

For good battery discharge performance at high rates and high power, a low specific surface resistance is desirable. Thinner standoffs tend to have lower strengths, but the standoff must also be strong enough, limiting how thin the standoff can be. Preferably, the specific surface resistance is not more than 4.3 O.cm², more preferably not more than 4.0 O.cm², and most preferably not more than 3.5 O.cm².

ES 2 304 697 T3

Separator membranes for use in lithium batteries are often made of polypropylene, polyethylene, or ultra-high molecular weight polyethylene, with polyethylene being preferred. The spacer can be a single layer of biaxially oriented microporous membrane, or two or more layers can be laminated together to provide the desired tensile strengths in orthogonal directions. A single layer is preferred to minimize cost. A suitable single layer biaxially oriented polyethylene microporous separator is available from Tonen Chemical Corp., available from EXXON Mobile Chemical Co., Macedonia, NY, USA Setela grade F20DHI separator has a nominal thickness of 20 pm , and the quality 16MMS Setela has a nominal thickness of 16 pm.

The anode, cathode, and separator bands are combined together in an electrode assembly. The electrode assembly can be a spirally wound design, such as that shown in Figure 1, made by winding alternating bands of cathode, spacer, anode, and spacer around a mandrel, which is removed from the electrode assembly when winding is completed. It is wrapped around the exterior of the electrode assembly with at least one layer of spacer and / or at least one layer of electrically insulating film (eg, polypropylene). This serves several purposes: it helps hold the mount together, and can be used to adjust the width or diameter of the mount to the desired dimension. The outermost end of the spacer or other outer film layer can be secured with a piece of adhesive tape or by heat sealing.

Rather than being spirally wound, the electrode assembly can be formed by folding the electrode strips and spacer together. The bands can be aligned along their lengths, and then folded in an accordion fashion, or the anode and an electrode band can be positioned perpendicular to the cathode and another electrode band, and the electrodes alternately folded one across on the other (orthogonally oriented), in both cases forming a stack of alternating layers of anode and cathode.

The electrode assembly is inserted into the wrap container. In the case of a spiral wound electrode assembly, whether in a cylindrical or prismatic container, the main surfaces of the electrodes are perpendicular to the side wall (s) of the container (in other words, the core center of the electrode assembly is parallel to the longitudinal axis of the stack). Folded electrode assemblies are typically used in prismatic stacks. In the case of an accordion-folded electrode assembly, the assembly is oriented such that the flat surfaces of the electrodes at opposite ends of the stack of electrode layers are adjacent to opposite walls of the container. In these configurations, most of the total area of ​​the main surfaces of the anode is adjacent to most of the total area of ​​the main surfaces of the cathode, through the spacer, and the outermost parts of the main surfaces of the electrodes are adjacent to the side wall of the container. Thus, expansion of the electrode assembly due to an increase in the combined thicknesses of the anode and cathode is restricted by the wall (s) of the container.

A non-aqueous electrolyte, containing water only in very small amounts as a contaminant (for example, not greater than about 500 parts per million by weight, depending on the electrolyte salt being used), is used in the battery cell of the invention. Any nonaqueous electrolyte suitable for use with lithium and the active cathode material can be used. The electrolyte contains one or more electrolyte salts dissolved in an organic solvent. For a Li / FeS2 cell, examples of suitable salts include lithium bromide, lithium perchlorate, lithium hexafluorophosphate, potassium hexafluorophosphate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, and lithium iodide; and suitable organic solvents include one or more of the following: dimethyl carbonate, diethyl carbonate, ethyl and methyl carbonate, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate , methyl formate, γ-butyrolactone, sulfolane, acetonitrile, 3,5-dimethylisoxazole, N, N-dimethylformamide and ethers. The salt / solvent combination will provide sufficient electrolytic and electrical conductivity to meet the cell discharge requirements over the desired temperature range. Esters are often desirable because of their generally low viscosity, good wettability, good low temperature discharge performance, and good high rate discharge performance. This is particularly true of Li / FeS batteries.₂Because ethers are more stable than with MnO2 cathodes, thus larger amounts of ether can be used. Suitable ethers include, but are not limited to, acyclic ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, di (methoxyethyl) ether, triglyme, tetraglyme, and diethyl ether; and cyclic ethers such as 1,3-dioxolane, tetrahydrofuran, 2-methyl-tetrahydrofuran, and 3-methyl-2-oxazolidinone.

Accordingly, various combinations of electrolyte salts and organic solvents can be used to form the electrolyte for electrochemical cells. The molar concentration of the electrolyte salt can be varied to modify the conductive properties of the electrolyte. Examples of suitable non-aqueous electrolytes containing one or more electrolyte salts dissolved in an organic solvent include, but are not limited to, a solvent concentration of 1 mole per liter of lithium trifluoromethanesulfonate (14.60% by weight) in a solvent mixture of 1,3-dioxolane, 1,2-diethoxyethane, and 3,5-dimethylisoxazole (24.80: 60.40: 0.20% by weight), having a conductivity of 2.5 mS / cm; a solvent concentration of 1.5 moles per liter of lithium trifluoromethanesulfonate (20.40% by weight) in a solvent mixture of 1,3-dioxolane, 1,2-diethoxyethane, and 3,5-dimethylisoxazole (23, 10: 56.30: 0.20% by weight), which has a conductivity of 3.46 mS / cm; and a solvent concentration of 0.75 moles per liter of lithium iodide (9.10% by weight) in a solvent mixture of 1,3-dioxolane, 1,2-diethoxyethane, and 3,5-dimethylisoxazole (63 , 10: 27.60: 0.20% by weight), which has a conductivity of 7.02 mS / cm. The electrolytes used in the electrochemical cells of the present invention have a conductivity generally greater than about 2.0 mS / cm, desirably greater than about 2.5 or about

ES 2 304 697 T3 is approximately 3.0 mS / cm, and preferably greater than about 4, about 6, or about 7 mS / cm.

The compositions and specific amounts of anode, cathode, and electrolyte can be adjusted to provide the desired manufacturing, performance, and storage characteristics of the cell.

The stack can be closed and sealed using any suitable procedure. Such procedures may include, but are not limited to, crimping, re-embedding, "colleting", and combinations thereof. For example, for the battery of Figure 1, a flange is formed on the package after inserting the electrodes and insulating cone, and the gasket and cover assembly (which includes the battery cover, contact spring , and the purge sleeve) are attached to the open end of the container. The stack is held on the flange while the gasket and lid assembly are pushed down against the flange. The diameter of the top of the container above the bulge is reduced with a segmented "collet" ring to hold the gasket and lid assembly in place in the stack. After introducing the electrolyte into the cell through the openings in the purge sleeve and cap, a purge ball is inserted into the sleeve to seal the opening in the battery cap. A PTC device and a terminal cover are placed on the battery, above the battery cover, and the top edge of the container is bent inward with a crimp groove, to hold the gasket, the mounting of the cap, the PTC device, and the terminal cap, and complete the sealing of the open end of the container using the gasket.

The above specification is particularly relevant for Li / FeS batteries₂ cylindrical, such as types FR6 and FR03, as defined in the international standards IEC 60086-1 and IEC 60086-2, published by the International Electrotechnical Commission, Geneva, Switzerland. However, the invention can also be adapted to other sizes and shapes of stacks, and stacks with other designs of electrode assemblies, shells, seals, and pressure relief valves.

The characteristics of the invention and its advantages are illustrated in more detail in the following examples, in which, unless otherwise indicated, the experiments were carried out at room temperature:

Example 1

Cylindrical Li / FeS2 cells of the FR6 type, with spiral wound electrode assemblies, were manufactured with various void volumes of the electrode assembly per centimeter of interfacial height of the electrode assembly, over a range of approximately 0.373 to about 0.455 cm³/ cm. The void volumes were varied by adjusting the volume of voids within the active material mixture coated on the cathode. This was done with various combinations of mix, thickness and pack formulations. The separator material used in all stacks was highly crystalline polypropylene microporous material, with uniaxial orientation, with a nominal thickness of 25 µm.

Example 2

Samples of the cells of Example 1 were prepared for testing. For each group with a given void volume per unit height, some cells remained uncharged, and some cells were 50% discharged (discharged at a rate of 200 mA for the time needed to retire 50 percent of the estimated capacity). The non-discharged cells and the 50% discharged cells were tested in an impact test, and the external temperature of each of the tested cells was followed during the test, and for six hours after the test.

For the impact test, a sample stack is placed on a flat surface, a 15.8 mm diameter rod is placed through the center of the sample, and a 9.1 kg mass is dropped from a height 61 ± 2.5 cm above the sample. The sample stack is impacted with its longitudinal axis parallel to the flat surface, and perpendicular to the longitudinal axis of the 15.8 mm diameter rod placed through the center of the stack. Each sample is subjected to a single impact.

None of the batteries that did not discharge had an external temperature that exceeded 170 ° C. The percentage of batteries discharged to 50% whose external temperature exceeded 170 ° C was represented. The best curve that fit the points represented is shown in figure 2, in which the empty volume per unit height (in cm³/ cm) is on the abscissa axis, and the percentage of cells with an external temperature that exceeds 170 ° C is on the ordinate axis.

The results of the impact test show that as the empty volume of the electrode assembly decreases, the percentage of batteries with an external temperature that exceeds 170 ° C increases. From the graph of Figure 2, it would be expected that 0% of the cells with an empty volume of approximately 0.45 cm³/ cm of interfacial height would have an external temperature that exceeds 170 ° C, and above 60% with a void volume of approximately 0.37 cm³/ cm would be expected to exceed 170 ° C. The high external temperatures were attributed to damage to the separator resulting in internal shorts that generated heat.

ES 2 304 697 T3

A subsequent examination of both FR6 Li / FeS2 cells after different levels of discharge revealed that a net increase in the total volume of the electrodes in the FR6 cell, which increases as the discharge develops, causes bending and folding of the bands of the electrodes, and collapse of the central core of the electrode assembly by the time the batteries are 50% discharged. By contrast, a similar examination of Li / MnO cells₂ With spiral wound electrodes, it showed little if any discernible change in the electrode mounting at 50% discharge. The difference between the volumes of the active materials and the volumes of the discharge reaction products provides an explanation for the difference in the effects of discharge in spiral wound electrode assemblies in Li / FeS2 stacks vs. Li / FeS2.

Example 3

Four batches of FR6 batteries were manufactured, each with a separator made from a different material. A description of the spacer materials is provided in Table 1, and typical spacer properties, as determined by the methods described below, are summarized in Table 2. The spacer material used for Lot A is the same than used in the batteries in Example 1. Each cell contained approximately 1.60 g of electrolyte, the electrolyte consisting of 9.14 percent by weight of Li salt in a solvent mixture of 1,3-dioxolane, 1,2-dimethoxyethane, and 3,5-dimethylisoxazole (63 , 05: 27.63: 0.18 by weight).

TABLE 1

<td>Lot A</td><td>Lot B</td><td>Lot C</td><td>Lot D</td>

<td>Highly crystalline microporous polypropylene, with uniaxial orientation, 25 pm thick</td><td>highly crystalline microporous polypropylene, with uniaxial orientation, 20 pm thick</td><td>20 pm thick, ultra-high molecular weight amorphous microporous polyethylene, biaxially oriented</td><td>amorphous microporous polyethylene, with biaxial orientation, 20 pm thick</td>

TABLE 2

<td>Property (units)</td><td>Lot A</td><td>Lot B</td><td>Lot C</td><td>Lot D</td>

<td>Porosity (%)</td><td> 38</td><td> 38</td><td> 42</td><td> 40</td>

<td>Maximum effective pore size (pm)</td><td> 0,10</td><td> 0,06</td><td> 0,38</td><td> 0,10</td>

<td>Dielectric breakdown voltage (V)</td><td> 2700</td><td> 2200</td><td> 1600</td><td> 2625</td>

<td>Tensile stress, TD</td><td> 1863</td><td> 1589</td><td> 8277</td><td> 13102</td>

<td>N / cm² (kgf / cm²)</td><td> (190)</td><td> (162)</td><td> (844)</td><td> (1336)</td>

<td>Tensile stress, TD</td><td> 4,66</td><td> 3, 18</td><td> 16, 55</td><td> 26, 20</td>

<td>N / cm (kgf / cm)</td><td> (0,475)</td><td> (0,324)</td><td> (1,688)</td><td> (2,672)</td>

<td>Tensile stress, MD</td><td> 16544</td><td> 26195</td><td> 15113</td><td> 17927</td>

<td>N / cm² (kgf / cm²)</td><td> (1687)</td><td> (2671)</td><td> (1541)</td><td> (1828)</td>

<td>Tensile stress, MD</td><td> 41,37</td><td> 52,39</td><td> 30, 23</td><td> 35, 85</td>

<td>N / cm (kgf / cm)</td><td> (4,218)</td><td> (5,342)</td><td> (3,082)</td><td> (3,656)</td>

<td>Elongation at break, TD (%)</td><td> 1000</td><td> 790</td><td> 440</td><td> 320</td>

<td>Elongation at break, MD (%)</td><td> 120</td><td> 54</td><td> 260</td><td> 225</td>

<td>Surface specific resistance (Ω.αη²)</td><td> 4,59</td><td> 2,71</td><td> 3,06</td><td> 2, 90</td>

<td>BET specific surface (m²/ g)</td><td> 44,0</td><td> 48, 9</td><td> 16, 2</td><td> 36, 4</td>

The same stack design was used for all batches AD. The cell design was one with higher amounts of active materials, a higher concentration of FeS2 in the cathode mix, and an increase in super

ES 2 304 697 T3 interfacial efficiency of the electrode, as well as a ratio between the total introduced capacity of the anode: lower cathode, than the cells of Example 1, with a ratio between the void volume of the electrode assembly and the interfacial height of approximately 0.452, which results in a 22% increase in the interfacial capacity of the stack.

Example 4

Stacks of each batch of Example 3 were discharged 50%, and then tested with the impact test. The percentage of piles that exceeded 170 ° C in the test was 20% for batch A, 80% for batch B, and 0% for batches C and D.

Increasing the interfacial capacity by 22% compared to batteries of example 1 with a quotient between the void volume of the electrode assembly and the interfacial height of approximately 0.452, the percentage of batteries that exceeded 170 ° C in the impact test increased from 0% to 20%. Stacks in batch A had a reduced amount of void space to accommodate a net increase in the volume of the discharge reaction products, compared to the volume of the unreacted active materials, increasing the adverse effects of discharge on assembly. of Li / FeS2 electrodes observed in Example 2.

The reduced thickness of the separator material in batch B compared to batch A contributed to a further increase in the percentage of piles that exceeded 170 ° C in the impact test, from 20% to 80%.

Although the thicknesses of the separator materials in batches C and D were the same as the thickness of the separator in batch B, there were no stacks in either batch C or batch D. The results for lots C and D were comparable to those of the cells of Example 1, with a ratio between the void volume of the electrode assembly and the interfacial height of approximately 0.452, even though the void volume within the cathode and the thickness of separator material were both reduced in batches C and D.

Example 5

Three lots of FR6 cells were used to compare the actual performance of FR6 cells in relatively low-rate and high-rate discharge tests. The first batch was batch D from Example 3. The characteristics of batch D are summarized in Table 3. The values ​​indicated are nominal values, and may vary within typical manufacturing tolerances.

Batches E and F batteries were manufactured according to the prior art. The stacks in batch F were as in Example 1, with a ratio of the void volume of the electrode assembly to the interfacial height of approximately 0.452. The characteristics of lots E and F are shown in table 3. In batch E the same separator material was used as in batch F, but in batch E the composition of the cathode mixture was modified, and the interfacial capacity increased by 18% compared to batch F. The use of a thinner spacer (20 pm thick) in batch D allowed a 22% increase in the interfacial capacity of the pile, compared to batch F.

(Table goes to next page)

ES 2 304 697 T3

TABLE 3

<td>Characteristic</td><td>Lot D</td><td>Lot E</td><td>Lot F</td>

<td>Anode</td><td>Li-Al</td><td>Li-Al</td><td>Li-Al</td>

<td>Li sheet thickness (cm)</td><td> 0,01524</td><td> 0,01524</td><td> 0,01524</td>

<td>Lithium foil width (cm)</td><td> 3,899</td><td> 3, 899</td><td> 3, 861</td>

<td>Length of cut Li sheet (cm)</td><td> 31, 50</td><td> 30,48</td><td> 30, 61</td>

<td>Li foil weight (g)</td><td> 0, 99</td><td> 0, 97</td><td> 0, 95</td>

<td>Li / battery input capacity (mAh)</td><td> 3859</td><td> 3735</td><td> 3664</td>

<td>Anode / Cell Interfacial Capacity (mAh)</td><td> 3600</td><td> 3485</td><td> 3470</td>

<td>Cathode</td><td></td><td></td><td></td>

<td>Al current collector thickness (cm)</td><td> 0,00254</td><td> 0,00254</td><td> 0,00254</td>

<td>Current collector volume (cm³)</td><td> 0,3313</td><td> 0,3199</td><td> 0,3186</td>

<td>Dry coating (% by weight): FeS₂</td><td> 92,00</td><td> 92,00</td><td> 92,75</td>

<td>Acetylene black</td><td> 1, 40</td><td> 1, 40</td><td> 2,5</td>

<td>Graphite</td><td>4.00 MX15</td><td>4.00 MX15</td><td>2.25 KS6</td>

<td>Binder</td><td>2.00 SEBS</td><td>2.0 SEBS</td><td>2.00 PEPP</td>

<td>Other</td><td>0.3 PTFE</td><td>0.3 PTFE</td><td>0.05 PEO</td>

<td>Other</td><td>0.3 silica</td><td>0.3 silica</td><td></td>

<td>Actual coating density (g / cm³)</td><td> 4,115</td><td> 4,115</td><td> 4,116</td>

<td>Coating thickness (each side) (cm)</td><td> 0,0080</td><td> 0,0080</td><td> 0,0072</td>

<td>Coating loading (mg / cm²)</td><td> 21,26</td><td> 21,26</td><td> 16, 98</td>

<td>Coating packing (%)</td><td> 64</td><td> 64</td><td> 57</td>

<td>Cladding width (cm)</td><td> 4,077</td><td> 4,077</td><td> 4,039</td>

<td>Cathode (coating) length (cm)</td><td> 29,85</td><td> 28, 83</td><td> 28, 96</td>

<td>Liner / Pile Weight (g)</td><td> 5, 17</td><td> 5, 00</td><td> 3, 97</td>

<td>Cathode / Cell Input Capacity (mAh)</td><td> 4250</td><td> 4110</td><td> 3290</td>

<td>Cathode / cell interfacial capacity (mAh)</td><td> 4005</td><td> 3877</td><td> 3105</td>

<td>Separator (2 shards / stack)</td><td></td><td></td><td></td>

<td>Material</td><td>PE 20</td><td>PP of 25</td><td>PP of 25</td>

<td></td><td>p.m</td><td>p.m</td><td>p.m</td>

<td>Length / fragment (cm)</td><td> 39, 5</td><td> 39</td><td> 39</td>

<td>Width / fragment (cm)</td><td> 44</td><td> 44</td><td> 44</td>

<td>Total volume (cm³)</td><td> 0, 431</td><td> 0,425</td><td> 0, 532</td>

<td>Electrode mounting</td><td></td><td></td><td></td>

<td>Winding mandrel diameter (cm)</td><td> 0,4</td><td> 0,4</td><td> 0,4</td>

<td>Overwrap volume (cm³)</td><td> 0, 124</td><td> 0, 124</td><td> 0, 124</td>

<td>Interfacial height (cm)</td><td> 3,899</td><td> 3,899</td><td> 3,861</td>

<td>Container</td><td>Steel</td><td>Steel</td><td>Steel</td>

<td></td><td>nickel plated</td><td>nickel plated</td><td>nickel plated</td>

<td>Thickness (cm)</td><td> 0,0241</td><td> 0,0241</td><td> 0,0241</td>

<td>Outside diameter (cm)</td><td> 1,392</td><td> 1,392</td><td> 1,379</td>

<td>Inner diameter (cm)</td><td> 1,344</td><td> 1,344</td><td> 1, 331</td>

<td>Battery</td><td></td><td></td><td></td>

<td>Internal void volume (%)</td><td> 10</td><td> 10</td><td> 12</td>

<td>Anode / cathode input capacity</td><td> 0, 95</td><td> 0, 95</td><td> 1,18</td>

<td>Interfacial capacity (mAh)</td><td> 3600</td><td> 3485</td><td> 3105</td>

<td>Cathode capacity / interfacial volume (mAh / cm³)</td><td> 724</td><td> 701</td><td> 578</td>

ES 2 304 697 T3

Example 6

Batteries of each of lots D, E, and F were continuously discharged at 200 mA down to 1.0 volts, and continuously at 1000 mA down to 1.0 volts. Table 4 compares the results.

TABLE 4

<td>Test</td><td>Lot D</td><td>Lot E</td><td>Lot F</td>

<td>200 mA</td><td>3040 mAh</td><td>2890 mAh</td><td>2417 mAh</td>

<td>1000 mA</td><td>2816 mAh</td><td>2170 mAh</td><td>2170 mAh</td>

The following properties of the separator material are determined according to the corresponding methods. Unless otherwise specified, all described properties are determined at room temperature (20-25 ° C).

• Tensile stress was determined using an Instron Model 1123 Universal Testing Machine, per ASTM D882-02. The samples were cut to 1.27 cm (0.50 inches) by 4.45 cm (1.75 inches). The initial jaw spacing was 2.54 cm (1 inch), and the draw rate was 5.08 cm (2 inches) per minute. Tensile stress was calculated as applied force divided by the initial cross-sectional area (the width of the sample perpendicular to the applied force times the thickness of the sample).

• The maximum effective pore diameter was measured on images produced at a magnification of 30,000 times, using a scanning electron microscope, and covering a surface area of ​​4 pm x 3 pm. For each separator sample, an image of both major surfaces was produced. The largest pores on each image were measured to determine the largest circular diameter that would fit within the pore wall (the maximum effective diameter of the individual pores). The maximum effective pore diameter of the sample was calculated by averaging the maximum effective pore diameters of the two largest pores on each face (ie, the average of four individual pores).

• Porosity was determined by (1) cutting a sample from the separator, (2) weighing the sample, (3) measuring the length, width, and thickness of the sample, (3) calculating the density from the weight and measurements, (4) dividing the calculated density by the theoretical density of the separator polymer resin, provided by the separator manufacturer, (5) multiplying the dividend by 100, and (5) subtracting this value from 100.

• The breakdown voltage of the dielectric was determined by placing a sample of the separator between two stainless steel poles, each 2 cm in diameter, and with a circular flat end, and applying an increasing voltage across the poles, using a machine Quadtech Model Sentry 20 hipot test, and recording the displayed voltage (the voltage at which an arc of current occurs through the sample).

• Elongation at break was determined using an Instron Model 1123 Universal Testing Machine in accordance with ASTM D882-02. The samples were cut to 1.27 cm (0.50 inches) by 4.45 cm (1.75 inches). The initial jaw spacing was 2.54 cm (1 inch), and the draw rate was 5.08 cm (2 inches) per minute. Elongation at break was calculated by subtracting the initial length of the sample from the length of the sample at break, dividing the remainder by the initial length of the sample, and multiplying the dividend by 100 percent.

• Specific surface resistance (ASR) was determined for separator samples suspended in an electrolyte, between two platinum electrodes, using a Model 34 Conductance-Resistance Meter, from Yellow Springs Instrument, Yellow Springs, OH, USA. to perform resistance measurements. The electrolyte solution used was 9.14 weight percent LiI salt, in a solvent mixture of

1,3-dioxolane, 1,2-dimethoxyethane, and 3,5-dimethylisoxazole (63.05: 27.63: 0.18 by weight). All tests were done in an atmosphere of less than 1 part per million water and less than 100 parts per million oxygen. An electrically insulating sample holder, designed to hold the separator sample with an area of ​​1.77 cm, was immersed² of the exposed separator, in the electrolyte solution, so that the part of the support to hold the sample was arranged midway between two platinum electrodes, 0.259 cm apart. The resistance between the electrodes was measured. The electrolyte holder was removed, a separator sample was inserted into the holder, and the holder was slowly lowered into the electrolyte solution to the same set level, so that the sample was completely flooded with electrolyte without trapped gas bubbles. in the sample. Resistance was measured. ASR was calculated using the formula:

ES 2 304 697 T3

ASR = A (R₂ - R₁ + pL / A) where A is the surface of the exposed stripper sample, R2 is the strength value with the film present, Ri is the strength value without the film, L is the thickness of the stripper sample, and p is the conductivity of the electrolyte used.

• The specific surface area was determined by the BET method, using a TriStar gas adsorption analyzer, from Micromeritics Instrument Corporation, Norcross, GA, USA and cut into pieces less than 1 cm² a 0.1 g to 0.2 g sample of the separator, to fit into the sample holder, the sample was degassed with a nitrogen jet at 70 ° C for 1 hour, and a distribution analysis of pore sizes, using nitrogen as the adsorbent gas, and collecting the complete adsorption / desorption isotherms.

Example 7

Cylindrical lithium / FeS2 cells of the FR6 type, with spiral wound electrode assemblies, were constructed with FeS particles₂ of various mean particle sizes, 22 pm (control), FeS₂ coarse size 75 pm, FeS₂ milled media between 5 and 10 pm (calculated estimate), and FeS₂ 4.9 pm jet ground. The stacks were identical to the Stacks in Lot D of Table 3, except for the mean FeS2 particle size and the typical and expected variation of the procedure. Figures 3a and 3b are cross-sectional SEM photographs of coated cathodes made with conventional cathode slurry mixtures (unmilled) and media milled, respectively.

The discharge time of each cell was tested using the DSC test at 1500/650 mW 2/28 sx 10 per hour, described above in the present invention. The results are illustrated in Tables 5a and 5b. Two series of pile tests containing media milled FeS2 were carried out.

TABLE 5a

<td></td><td colspan="3">FeS2 mean particle size</td><td></td>

<td></td><td>Thick</td><td>Witness</td><td>Jet milled</td><td>Improvement</td>

<td>Service FEP</td><td>MV = 75 pm</td><td>MV = 22 pm</td><td>MV = 4.9 pm</td><td></td>

<td>1.2 V</td><td>37 min</td><td>194 min</td><td>296 min</td><td> 1,52</td>

<td>1.1V</td><td>175 min</td><td>288 min</td><td>332 min</td><td> 1,15</td>

<td>1.05 V</td><td>214 min</td><td>314 min</td><td>340 min</td><td> 1,08</td>

<td>1.0 V</td><td>243 min</td><td>331 min</td><td>345 min</td><td> 1,04</td>

TABLE 5b

<td>Service FEP</td><td>Witness 22 pm</td><td>Media mill grind 5-10 pm</td><td>Improvement</td><td>Witness 22 pm</td><td>Media Mill Grind 5-10 pm 510 pm</td><td>Improvement</td>

<td>1.2 V</td><td>188 min</td><td>236 min</td><td> 1, 25</td><td>184 min</td><td>230 min</td><td> 1,25</td>

<td>1.1v</td><td>281 min</td><td>311 min</td><td> 1,11</td><td>277 min</td><td>304 min</td><td> 1, 10</td>

<td>1.05 V</td><td>305 min</td><td>329 min</td><td> 1,08</td><td>300 min</td><td>322 min</td><td> 1,07</td>

<td>1.0 V</td><td>318 min</td><td>338 min</td><td> 1, 06</td><td>314 min</td><td>331 min</td><td> 1,05</td>

As is evident from Tables 5a and 5b, it is illustrated that stacks prepared with the jet milled and media milled FeS2 particles provide a substantially longer discharge time of up to 1.05 volts, when compared to the jet ground particles. by FeS₂ Prior art control, 22 pm mean particle size, and FeS particles₂ coarse in size, 75 pm average particle size. Stacks containing FeS₂Media milling also maintained a shear voltage of&gt; 1.2 for an average of 69.6% of the service time&gt; 1 volt, while the control maintained only such a voltage for an average of 58.9% of the time. of service. Also, the stack containing FeS₂ Jet grinding maintained a cutoff voltage of&gt; 1.2 for 85.7% of the discharge time&gt; 1 volt.

ES 2 304 697 T3

Example 8

FR6 type lithium / FeS2 cylindrical cells were constructed with spiral wound electrode assemblies. The average particle size of FeS2, the composition of the electrolyte, and the thickness of the separator were varied, as shown in table 6. The rest of the characteristics of the batteries were the same as those described for batch D of the table. 3, except for the typical and expected variation of the procedure. Stacks 1-4 represent prior art stacks.

TABLE 6

<td>Battery</td><td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td><td>θ</td><td>ff</td><td> 8</td><td> 9</td><td> 10</td><td> 11</td><td> 12</td><td> 13</td><td> 14</td><td> 15</td><td> 16</td>

<td>FeS mean particle size₂</td><td></td><td> 22</td><td>μη</td><td></td><td colspan="4">5-10 pm * (media mill ground)</td><td></td><td> 22</td><td>p.m</td><td></td><td colspan="4">5-10 pm * (media mill ground)</td>

<td>Separator thickness (pm)</td><td> 50</td><td> 25</td><td> 20</td><td> 16</td><td> 50</td><td> 25</td><td> 20</td><td> 16</td><td> 50</td><td> 25</td><td> 20</td><td> 16</td><td> 50</td><td> 25</td><td> 20</td><td> 16</td>

<td>Electrolyte</td><td colspan="7">1.5 moles per liter of lithium trifluoromethanesulfonate solvent (20.4% by weight) in 1, dioxolane, 1,2-diethoxyethane 3,5-dimethylisoxazole (23.1: 56.4: 0.2% by weight )</td><td>3- , Y</td><td colspan="8">0.75 moles per liter of lithium iodide solvent (9.1% by weight) in 1,3-dioxolane, 1,2-diethoxyethane, and 3,5-dimethylisoxazole (63.1: 27.6: 0.2% in weigh)</td>

* (calculated estimate)

Each cell was tested using the DSC test at 1500/650 mW 2/28 s x 10 per hour. The effect of the electrolyte-separator resistance and the FeS2 particle size is illustrated in Figure 4. The representation of the cell groups illustrates that reducing the thickness of the separator, the use of FeS2 particles of average particle size relatively small, as well as the type of electrolyte, individually affect the efficiency of the cathode. In Figure 4, the lowermost line is a representation of the line that best fits the experimental results for stacks 1-4. Also, the remaining lines, in ascending order, represent results for stacks 5-8, 9-12, and 13-16, respectively.

Example 9

The anode voltage of cylindrical lithium / FeS cells was measured during the life of the batteries.₂ FR6 type, with spiral wound electrode assemblies. The cells were of substantially identical construction to that shown in Lot D of Table 3, except that one cell was constructed of medium-sized particles of FeS.₂ 22 pm, a second pile used FeS particles₂ mill-milled medium-size media between 5 and 10 pm (calculated estimate), and the third pile used FeS particles₂ 4.9 pm mean size jet milled, and typical and expected process variation. The anode voltage of each cell was plotted as a function of the discharge depth, as shown in Figure 5. The total cell voltage, as a function of the discharge depth, is plotted in Figure 6. The procedures of assays have been shown above in the present invention.

At 50% depth of discharge, the anode voltage is reduced by 40 millivolts when the mean particle size is reduced from 22 to 5.2 pm. Reducing the mean particle size of FeS₂ from 22 pm to 4.9 pm, it reduced the anode voltage by 150 millivolts. Electrochemical cells of size L92 were constructed and tested in a similar manner. The use of FeS2 with the mean particle size ranges described in the present invention was found to increase the overall pile stress at any given discharge depth, regardless of the size of the pile.

Example 10

The average particle size of FeS2, although strongly influences the high performance of the cell under normal environmental conditions, has an even greater influence at low temperatures. Table 7 below compares two different studies of mill-ground cathodes of medium particle size media between 5 and 10 pm (calculated estimate), and FeS₂ witness of mean particle size of 22 pm, and the performance of the pile as a function of temperature. The stacks were constructed in a manner substantially similar to that described for batch D of Table 3, except for the typical and expected variation of the procedure. The essay is a simulated standard application

ES 2 304 697 T3

Proposed DSC-ANSI, predefined (1500mW / 650mW) up to 1.05 volts. Although reducing the particle size improves performance by 5% or more under ambient conditions, improvements above 600% are observed at -20 ° C.

TABLE 7

<td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td></td><td>Witness</td><td>(ground in a media mill)</td><td>List of benefits</td><td>Witness</td><td>(ground in a media mill)</td><td>List of benefits</td>

<td>Temperature</td><td>min</td><td>min</td><td></td><td>min</td><td>min</td><td></td>

<td>21 ° C</td><td> 304</td><td> 325</td><td> 1,07</td><td> 302</td><td> 318</td><td> 1,05</td>

<td>0 ° C</td><td> 178</td><td> 227</td><td> 1,27</td><td> 186</td><td> 121</td><td> 1,14</td>

<td>-20 ° C</td><td> 14</td><td> 102</td><td> 7,28</td><td> 16</td><td> 100</td><td> 6,25</td>

Those practicing the invention and those skilled in the art will understand that various modifications and improvements can be made to the invention, without departing from the spirit of the concept described.