United States Statutory Invention Registration [11] 1431

Plichta et al.

[19]

H452 Apr. 5, 1988

Reg. Number: Published:

[54] CATHODE INCLUDING A NON FLUORINATED LINEAR CHAIN POLYMER AS THE BINDER, METHOD OF MAKING THE CATHODE, AND LITHIUM ELECTROCHEMICAL CELL CONTAINING THE CATHODE

Attorney, Agent, or Firm—Sheldon Kanars; Jeremiah G. Murray; Roy E. Gordon [57] ABSTRACT

[75] Inventors: Edward J. Plichta, Freehold; Mark

method including the steps of (A) dissolving the non ?uorinated linear chain polymer

Salomon, Fairhaven, both of NJ.

[73]

Assignee:

The United States of America as

represented by the Secretary of the Army, Washington, DC.

[21] Appl. No.: 895,015 Aug, 7, 1986 [22] Filed:

[56]

(B) adding the active cathode material and carbon and evaporating the solvent, and (C) grinding the dried mixture into a ?ne powder and making it into a cathode by pressing the powdered mixture onto both sides of an expanded metal screen The cathode can be combined with lithium as the anode and a solution of 0.8 mol dm-3 LiAlC14 in a mixed

Division of Ser. No. 749.597, Jun. 27, 1985. .

in a non polar solvent at a temperature near the melt

ing point of the polymer,

and then cutting to the desired dimensions.

Related US. Application Data

[62] [5 1] 152] [58]

A cathode suitable for use in a lithium electrochemical cell is made from a mixture of active cathode material, carbon, and non ?uorinated linear chain polymer by a

organic solvent of 24 mass percent 4-butyrolactone in l,

....... .. H01M 4/82

2 dimethoxyethane as the electrolyte to provide a me

................ .. 141/1.1; 141/1

chanically stable, relatively inexpensive lithium electro chemical cell having good cell performance.

Field of Search ............. .. 429/194, 197, 212, 217;

141/ 1.1

1 Claim, 1 Drawing Sheet

References Cited U.S. PATENT DOCUMENTS 3/1975 Kamenski .... ..

429/ 194

4,201,839 5/ 1980 Johnson et a1.

3,873,369

.... .. 429/ 194

4,223,080

9/1980 Auborn

.. 429/217 X

4,322,317

3/1982

Rao et al. .... ..

.. 429/212 X

4,463,072

7/1984

Gifford ct al. . . . .

. . . . .. 429/ 194

4,499,160

2/1985

Babai et al. ................... .. 429/217 X

A statutory invention registration is not a patent. It has the defensive attributes of a patent but does not have the enforceable attributes of a patent. No article or advertise ment or the like may use the term patent, or any term

suggestive of a patent, when referring to a statutory in vention registration. For more speci?c information on the

Primary Examiner-John F. Terapane

rights associated with a statutory invention registration

Assistant Examiner-Susan Woli'fe

see 35 U.S.C. 157.

Pc1eluarzthonlde

18

2B

3B

Discharge cycle number

4B

5B

H452

2

1 CATHODE INCLUDING A NON FLUORINATED LINEAR CHAIN POLYMER AS THE BINDER, METHOD OF MAKING THE CATHODE, AND LITHIUM ELECTROCHEMICAL CELL CONTAINING THE CATHODE

ture near the melting point of the polymer (100° to 150° C.). The active cathode material and carbon are added and the solvent evaporated. 5

The invention described herein may be manufac

DESCRIPTION OF THE PREFERRED EMBODIMENT The following is a preparation of a cathode structure utilizing TiSz as the active cathode material. The proce dure is performed in an argon ?lled dry box. Polypro

tured, used, and licensed by or for the Government for governmental purposes without the payment to us of 10 pylene powder is dissolved near its crystalline melting temperature of about 100° to 120° C. in a small volume any royalty thereon. of decahydronaphthalene of about 5 mils decahydro This application is a division of application Ser. No. naphthalene for about 0.1 to 0.2 gm (PP), the solution 749,597, ?led June 27, 1985. This invention relates to a cathode including a non ?uorinated linear chain polymer as the binder, to a method of making the cathode, and to a lithium electro

chemical cell containing the cathode.

being stirred continuously during heating. Once the (PP) is dissolved, the solution is removed from the heat and cooled below 100'’ C. and the active cathode mate rial and carbon powders are then added quickly before

the polymer solution cools completely. The powdered

BACKGROUND OF THE INVENTION

Existing technology for the fabrication of cathodes for use in lithium primary and secondary cells utilizes Teflon as the binding material. Teflon or polytetra?uo roethylene is expensive although inert, and its use re sults in cathode structures of poor mechanical stability. These problems do not easily lend themselves to the 25

large scale production of cathodes in manufacturing. SUMMARY OF THE INVENTION The general object of the invention is to provide a

materials and solutions are stirred vigorously by hand until the solution is absorbed and the mix becomes gran ular and has cooled to room temperature. The mixture is then dried in a vacuum oven at about 120° to 150° C.

for 12 hours in order to remove the decahydronaphthal ene. The dried mixture is then ground into a ?ne pow

der and made into cathodes by pressing the powdered mixture onto both sides of an expanded metal screen and then cut to desired dimensions.

.

Although ?at plate type electrodes have been pre pared in the foregoing embodiment to demonstrate the

cathode suitable for use in lithium electrochemical cells. 30 use of the non ?uorinated linear chain polymers as bind

Another object of the invention is to provide such a

cathode that will be mechanically stable and relatively inexpensive to manufacture. A further object of the

ing materials, the method results in moderately ?exible structures which makes the method equally adaptable to. the preparation of rolled electrodes, either cold

rolled or rolled through heated rollers using a pow invention is to provide such a cathode that will be suit 35 dered mix or a slurry mixture using a non reactive or~ able for use in a primary or secondary lithium cell. ganic solvent. It has now beenfound that the aforementioned ob-~ The TABLE shows typical results for a Li-TiSz cell jects can be attained by replacing the Te?on binder with a ncn fluorinated linear chain polymer such as

in which cell performance is studied as a function of

polypropylene (PP) or polyethylene (PE).

solvent composition, cathode composition, and cathode preparation, that is, cold-pressing or hot-pressing. Per

More particularly, according to the invention, a cath 40 ode for use in lithium primary or secondary cells can be

formance is found to be equal to that obtained from cells

prepared from a mixture of active cathode material,

utilizing cathodes of poor mechanical properties, that is,

conductive dilutant such as carbon and non ?uorinated linear chain polymer. The amount of carbon can be

based on teflon binders. The TABLE shows that one can operate with a wide range of (PP) content in the

varied depending upon the resistivity of the cathode 45 electrode. More speci?cally, one can use less binder and still obtain a good mechanically stable cathode. In fact, material and desired porosity of the ?nal cathode struc— ture. Typical cathode materials that can be used are

one can go down to as little as l to 3 weight percent of

metal halides, oxides and sul?des. The polymer is ?rst

binder which allows one to put in more active cathode

dissolved in a non polar solvent such as Decalin (Deca hydronaphthalene) or tetrachloroethylene at a tempera

material and improve the performance of the cell. TABLE

Performance Data for Li-TiSz Cells Utilizing Polypropylene (PP) as the Cathode Binder".

Electrode

Typeb

t/oc

cold-pressed

25 25 —20 —-30

cold-pressed

25 25

cold-pressed

25

'

Mass %

Mass %

Mass %

Current

Cathode

Electrolyte

TiSz

Carbon

PP

Density: mA/cm2

Efficiency

0.8 mol dm-3 LiAlCl4 in 24% 4-BL/DME

80

10

10

5.0 2.0 20 2.0

1.6 mol dni'3 LiAsF6 in 2Me—THF 1.3 mol din‘3

78.5

10

11.5

2.0 1.0

49.3 75.2 39.5 5.6 66.7 82.0

83.3

9.6

7.1

1.0

71.1

81.8

12.7

5.5

2.0

69.5

LiAsF6 in cold-pressed

25

2Me—-THF 1.6 mol dm ‘3

LiAsF6 in '

cold-pressed

25

2Me-THF

1.2 mol di'n-3 LiAsF6 in

'

87.3

10.0

2.7

1.0

80.2

H452 3

4 TABLE-continued

Performance Data for Li-TiS; Cells Utilizing Polypropylene (PP) as the Cathode Binder‘. Mass % Mass % Mass %

Electrode

Typeb

t/oc

cold-pressed

25

Current

Cathode

Electrolyte

TiSz

Carbon

PP

Density: mA/cm2

Ef?ciency

0.85 mol dm"3 LiAlCl4 in 24% 4-BL/DME

79.7

10.1

10.2

2.0

68.9

"2Me--THF is Z-methyl tetrahydrofuran DME is l.2¢dimethoxyerhane MRI. is 4-bulyrollctone bCathode porosity in the range of 40-60%

In the method of the invention, mechanically stable structures can be easily prepared by cold-pressing or 15

cold rolling, and by hot-pressing or hot-rolling. More

DESCRIPTION OF THE DRAWING over, sintering temperatures below l70° C. should be used since some cathode materials are subject to decom The drawing illustrates a cycling pro?le for a re position above 200“ C. chargeable lithium cell using a TiSz cathode and an Thus, it has been demonstrated that non ?uorinated electrolyte consisting of 0.8 mol dm-3 LiAlCl4 in a mixed organic solvent of 24 mass percent 4-butyrolac 20 linear chain polymers such as (PP) or (PE) can be used to prepare mechanically stable cathodes for nonaqueous tone in 1,2 dimethoxyethane (24% 4~BL in DME). The lithium cells. The use of the non fluorinated linear chain

cathode (80 mass % TiSz, 10 mass % carbon and 10

polymers as binders results in low cost cathodes giving mass % (PP) is prepared as described in the description equal electrochemical performance as do Te?on of the preferred embodiment. Referring to the drawing, the cell used for the draw 25 bonded cathodes, but the use of the non ?uon'nated ing is cycled at 25' C. at a current density of 2.0 mA _ linear chain polymers results in cathodes having great mechanical stability that can be fabricated in several cm—2, and excursions are shown for discharges at 5.0 forms such as plates or rolls, and that can be made as mAcm-2 and at 2.0 mAcm-2 at lower temperatures of thin as 0.5 mm or less. -20‘ C. and ~30‘ C. Cycling is stopped after 33 cycles. The drawing also shows that after-excursions to higher 30 We wish it to be understood that we do not desire to be limited to the exact details as described for obvious current densities and/or lower temperatures, cell per

formance recovers exceptionally well. In the drawing,

modi?cations will occur to a person skilled in the art.

the ordinate, percent cathode utilization, is an indicator

What is claimed is:

as to how the cell is performing.

1. Method of preparing a cathode for use in a lithium

_

Any non ?uorinated linear chain polymer can be used 35 electrochemical cell from a mixture of TiSZ, carbon and polypropylene, said method including the steps of in the cathode that is stable in the electrolyte of the (A) dissolving polypropylene at 100° to 130° C. in a lithium cell. The linear chain polymers are inert in a small volume of decahydronaphthalene contained wide variety of non aqueous solvents including ethers in an argon ?lled dry box while stirring the solution and lactones. Suitable polymers include (PP) and (PE). continuously during heating, Active cathode materials that can be used include 40 (B) removing the solution from the heat, cooling to metal halides, metal oxides, and metal sul?des of which below 100° C., and quickly adding the carbon and TiSz is preferred. Pure carbon can be used for those TiSz before the polymer solution cools completely, cells in which the solvent serves as the depolarizer. (C) stirring the powdered materials and solution vig Any carbon black can be used as the carbon for the orously until the solution is absorbed and the mix cathode that enhances the conductivity of the elec 45 becomes granular and has cooled to room tempera trodes. The particular carbon black used in the descrip tion of the preferred embodiment is Shawinigan Black ture, (D) drying the mixture in a vacuum oven at 120° C. to but other high surface area carbons or graphite can also 150' C. for 12 hours in order to remove the decahy be used. The invention even contemplates a cathode dronaphthalene, and made from a mixture of polymer and active cathode SO (E) grinding the dried mixture into a ?ne powder and material with no carbon present. making into a cathode by pressing the powdered The electrolyte used in the lithium cell must be com mixture onto both sides of an expanded metal patible with the cathodes made according to the inven tion. Suitable electrolytes include a solution of an inor screen. a a a n t ganic lithium salt in a pure or mixed organic solvent.

65