Battery electrode and method of making

Claim 2

Carbon monofluoride (CF x ), acetylene black (Shawinigan), and PTFE (DuPont K-10 powder) were weighed out and placed into a grinding mortar. The proportions were as follows. CF x : acetylene black: PTFE (lg : 0.15g : 0.04g). These proportions are not critical, but it would be best to keep the level of PTFE as low as possible.

Claim 3

The mixture was ground with the pestle and this caused the PTFE to fibrillate. Fibrillation is the elongation of the PTFE particles into thin fibers or fibrils. These fibrils hold the other components of the mixture into a cohesive mass. Grinding was continued with occasional scraping of the walls of the mortar until the loose powders were totally collected into one mass and no loose powders remained.

Claim 4

The mixture was ground with the pestle and this caused the PTFE to fibrillate. Fibrillation is the elongation of the PTFE particles into thin fibers or fibrils. These fibrils hold the other components of the mixture into a cohesive mass. Grinding was continued with occasional scraping of the walls of the mortar until the loose powders were totally collected into one mass and no loose powders remained.

Claim 5

The mixture was then wet with a water/isopropanol solution to form a very thick paste. Usually one milliliter has been used in the past, but this amount may be varied. Other solution or solvents compatible with the components of the mixture could be used as the only purpose of the solution is to make the dry mixture more pliable and to create micropores in the electrode when the solution is removed by evaporation.

Claim 6

The mixture was then wet with a water/isopropanol solution to form a very thick paste. Usually one milliliter has been used in the past, but this amount may be varied. Other solution or solvents compatible with the components of the mixture could be used as the only purpose of the solution is to make the dry mixture more pliable and to create micropores in the electrode when the solution is removed by evaporation.

Claim 7

The wet mixture was then pressed out or calendered between two stainless steel platens. The pressure used was 5000 lbs. on the 6" x 6" square platens. The pressure which is used can be varied but should be sufficient to flatten the mixture into a thin sheet (less than 5 mils thick). The flattened sheet was then rolled up and folded into a small square and pressed out again. This pressing and rolling was repeated 6 times. The number of times the above calendering step must be repeated is variable; but should be repeated until the material looks uniform and has a leathery or rubber-like texture. After calendering the material in this manner, the fibrils that were created by high shear mixing are knit together to bind the mixture into one sheet.' A final pressing can be undertaken at this point with shims between the platens to control the final thickness of the electrode.

Claim 8

The wet mixture was then pressed out or calendered between two stainless steel platens. The pressure used was 5000 lbs. on the 6" x 6" square platens. The pressure which is used can be varied but should be sufficient to flatten the mixture into a thin sheet (less than 5 mils thick). The flattened sheet was then rolled up and folded into a small square and pressed out again. This pressing and rolling was repeated 6 times. The number of times the above calendering step must be repeated is variable; but should be repeated until the material looks uniform and has a leathery or rubber-like texture. After calendering the material in this manner, the fibrils that were created by high shear mixing are knit together to bind the mixture into one sheet.' A final pressing can be undertaken at this point with shims between the platens to control the final thickness of the electrode.

Claim 9

Any size or shape of electrode can be cut from the sheet and then can be bent or rolled into any shape before it is dried. After drying the sheets lose a very small amount of their flexibility; the amount depends on the bulk density of the material (this is controlled by the amount of liquid used in step 3 and the number of pressings used in step 4). In evaluating the electrochemical performance of these cathodes, a 0.5 inch I.D. Teflon Swagelok fitting was employed as a demountable cell body with two stainless steel pistons to back-up and make electrical contact to the cathode and anode buttons. The anode is a 0.5 inch button cut from lithium strip stock. The separator is cut the same size as the anode and is a 0.009 inch thick non-woven polypropylene absorber purchased from RAI Research Corp. The cathode is a 0.375 inch diameter button cut from a sheet of cathode material 0.020 inch thick. The electrolyte is a 1:1 mixture of propylene carbonate and dimethoxyethane containing 1 mole/liter of LiBF 4 . The cells are assembled in a dry box. Cells are discharged on a 10 Kohm load to a 2V cutoff and run for about 100 hours at this drain rate.

Claim 10

Any size or shape of electrode can be cut from the sheet and then can be bent or rolled into any shape before it is dried. After drying the sheets lose a very small amount of their flexibility; the amount depends on the bulk density of the material (this is controlled by the amount of liquid used in step 3 and the number of pressings used in step 4). In evaluating the electrochemical performance of these cathodes, a 0.5 inch I.D. Teflon Swagelok fitting was employed as a demountable cell body with two stainless steel pistons to back-up and make electrical contact to the cathode and anode buttons. The anode is a 0.5 inch button cut from lithium strip stock. The separator is cut the same size as the anode and is a 0.009 inch thick non-woven polypropylene absorber purchased from RAI Research Corp. The cathode is a 0.375 inch diameter button cut from a sheet of cathode material 0.020 inch thick. The electrolyte is a 1:1 mixture of propylene carbonate and dimethoxyethane containing 1 mole/liter of LiBF 4 . The cells are assembled in a dry box. Cells are discharged on a 10 Kohm load to a 2V cutoff and run for about 100 hours at this drain rate.

Claim 11

EXAMPLE 2 In a second example, approximately 80 grams of carbon monofluoride, 10 grams of acetylene black (Shawinigan), 2 grams of PTFE (Dupont K-10 powder) and 60 cc of water/isopropanol solution were intimately mixed. Approximately half the volume of the damped powders were into a C. W. Brabender, Inc. Plasti-Corder with a roller mixer-measuring head (60 ml. capacity) for high shear mixing. Mixing was carried out at room temperature (approximately 25°C) for 5 minutes at 20 rpm. After removing the fibrillated mixture from the mixer, a portion of the material was calendered as in Example 1. Electrodes made in this fashion perform in cell tests like those discribed in Example 1.

Claim 12

EXAMPLE 2 In a second example, approximately 80 grams of carbon monofluoride, 10 grams of acetylene black (Shawinigan), 2 grams of PTFE (Dupont K-10 powder) and 60 cc of water/isopropanol solution were intimately mixed. Approximately half the volume of the damped powders were into a C. W. Brabender, Inc. Plasti-Corder with a roller mixer-measuring head (60 ml. capacity) for high shear mixing. Mixing was carried out at room temperature (approximately 25°C) for 5 minutes at 20 rpm. After removing the fibrillated mixture from the mixer, a portion of the material was calendered as in Example 1. Electrodes made in this fashion perform in cell tests like those discribed in Example 1.

Claim 13

The types of pore forming liquids can be alcohols of 1-8C atoms, fluro-chloro carbons of 1 to 3C atoms, water, hexane, kerosines, light oils, and the like. Any liquid of mixture of liquids can be used provided the liquid or mixture wets the electrode material, can be removed by evaporation without leaving any residue, and does not react with any component of the mixture.

Claim 14

The types of pore forming liquids can be alcohols of 1-8C atoms, fluro-chloro carbons of 1 to 3C atoms, water, hexane, kerosines, light oils, and the like. Any liquid of mixture of liquids can be used provided the liquid or mixture wets the electrode material, can be removed by evaporation without leaving any residue, and does not react with any component of the mixture.

Claim 15

The fluorinated graphite or fluorinated carbon, CFx materials contemplated in the inventory also include those referred to in the art as (C 2 F) in active materials wherein "n" is an indefinitely large number as found in naturally occurring fluorinated carbonaceous materials.

Claim 16

The fluorinated graphite or fluorinated carbon, CFx materials contemplated in the inventory also include those referred to in the art as (C 2 F) in active materials wherein "n" is an indefinitely large number as found in naturally occurring fluorinated carbonaceous materials.

Claim 17

It is thus seen that the present invention affords a method and product having a significantly improved electrode. The advantages include the following aspects: 1. The sheet of electrode material is flexible making it ideally suited for use in cylindrical cells employing the so-called "jelly roll" configuration for the cathode-anode assemblies. In these cells a strip of the cathode and anode are laid one atop the other and the two strips are rolled up together to form a cylinderically-shaped cell element. Obviously, cathodes used in these cells must be flexible so that they will tolerate the rolling operation without breaking or spalling off the current collector. 2. The level of inert, electrically insulating binder (i.e., PTFE) is very low (less than 3% by wt.) so that good electrical conductivity is maintained. Typically, the higher the level of PTFE in an electrode the higher the voltage losses are for that electrode. The lower level of binder will also provide for more active material in the electrode and give electrodes with higher capacity per-unit volume. 3. The use of volatile solutions or solvents to wet the electrode is important because they are easily removed by evaporation. Evaporation will not disrupt the structure of the electrode. Residues of polymeric material and surfactants which could be detrimental to the performance or life of a battery are avoided. 4. This electrode formulation technique is amenable for use on plastic milling equipment and probably can be adapted to give sheet electrodes in a continuous process.

Claim 18

It is thus seen that the present invention affords a method and product having a significantly improved electrode. The advantages include the following aspects: 1. The sheet of electrode material is flexible making it ideally suited for use in cylindrical cells employing the so-called "jelly roll" configuration for the cathode-anode assemblies. In these cells a strip of the cathode and anode are laid one atop the other and the two strips are rolled up together to form a cylinderically-shaped cell element. Obviously, cathodes used in these cells must be flexible so that they will tolerate the rolling operation without breaking or spalling off the current collector. 2. The level of inert, electrically insulating binder (i.e., PTFE) is very low (less than 3% by wt.) so that good electrical conductivity is maintained. Typically, the higher the level of PTFE in an electrode the higher the voltage losses are for that electrode. The lower level of binder will also provide for more active material in the electrode and give electrodes with higher capacity per-unit volume. 3. The use of volatile solutions or solvents to wet the electrode is important because they are easily removed by evaporation. Evaporation will not disrupt the structure of the electrode. Residues of polymeric material and surfactants which could be detrimental to the performance or life of a battery are avoided. 4. This electrode formulation technique is amenable for use on plastic milling equipment and probably can be adapted to give sheet electrodes in a continuous process.

Claim 19

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

Claim 22

2 . The method of claim 1 wherein the extraction of said volatile pore forming liquid is effected during the formulation of said composition into the desired shaped electrode.

Claim 23

The method of claim 1 wherein from about 1 percent to about 25 percent by weight of electrical conductivity enhancing particulate material is added to said active material.

Claim 24

The method of claim 3 wherein the electrical conductivity enhancing material is acetylene black.

Claim 25

The method of claim 1 wherein the electrode active material is carbon monofluoride.

Claim 26

The method of claim 1 wherein the fluoropolymer is PTFE.

Claim 27

The method of claim 1 wherein the fluorinated polymer is present in amounts of from 0.5 percent to 4 percent by weight of the total composition.

Claim 28

The method of claim 4 wherein the fluoropolymer is PTFE.

Claim 29

A product made by the method of claim 1.

Claim 30

A product made by the method of claim 5.