WO1996020240A1

WO1996020240A1 - Polymer precursors for solid electrolytes

Info

Publication number: WO1996020240A1
Application number: PCT/US1994/014942
Authority: WO
Inventors: Benjamin Chaloner-Gill; Milton Neal Golovin; Joseph Lundquist
Original assignee: Valence Technology, Inc.
Priority date: 1994-12-27
Filing date: 1994-12-27
Publication date: 1996-07-04
Also published as: AU1407495A

Abstract

Polymer precursors for the solid polymer matrix of a solid electrolyte are acryloyl-derivatized urethane polymers made from isocyanate and a macroglycol of chemically linked blocks of poly(oxyalkylene) and/or polyester units. The linking groups are carbonate, bis-carbonate, phosphate, phosphonate, siloxy and sulfone groups.

Description

POLYMER PRECURSORS FOR SOLID ELECTROLYTES

Field of the Invention

The invention relates to polymers for solid polymeric electrolytes and their use in solid

electrochemical cells. The invention particularly relates to polymer precursors for single-phase solid polymeric electrolytes.

Background of the Invention

Solid electrolytes have been shown to have many advantages in the fabrication of electrochemical cells and batteries, such as thermostability, reduced

corrosion of the electrodes, and cyclability.

Furthermore, solid electrolytes permit us to create electrochemical sources of high energy per unit weight. Solid electrolytes, particularly polymeric

electrolytes, have the principal advantage of being prepared in thin layers which reduces cell resistance and allows large drains at low current densities.

In the design of solid polymeric electrolytes both the properties of ionic conductivity and mechanical strength must be provided. It has been found

advantageous to incorporate inorganic ion salts and solvents into the solid electrolytes, as well as to select polymers which enhance ionic conductivity.

Cross-linking of the polymers can lead to stronger solid electrolytes, i.e. resilient thin layers of electrolyte, but cross-linking must not be to the detriment of ionic conductivity. Thermal and

radiation-induced cross-linking (curing) have been extensively used for this purpose. Prior to

crosslinking, the polymer or oligomer is termed a prepolymer or polymer precursor. U.S. Patent 4,654,279 describes a two-phase solid polymeric electrolyte consisting of an interpenetrating network of a

mechanically supporting phase consisting of cross-linked polymers, and a separate ionic conducting phase consisting of a metal salt and a complexing liquid therefor, which is a poly(alkylene oxide).

Poly (alkylene oxide), optionally derivatized with acryloyl and urethane groups is a polymer precursor for single-phase polymeric electrolytes. U.S. Patent

4,908,283 discloses an acryloyl-derivatized solid polymeric electrolyte. However, radiation-cured solid polymeric electrolytes may lack sufficient mechanical strength and toughness. It is believed that the physical robustness of the cross-linked polymer is diminished by the presence of high molecular weight poly(oxyalkylene) units in the polymer precursors.

Such poly(oxyalkylene) units are referred to as the "soft sectors" of the cross-linked polymer precursors because of this physical property. The art is seeking means for strengthening the poly(oxyalkylene) portions of the polymer precursor.

The chemical cross-linking of poly(alkylene oxide), for example, as disclosed in U.S. Patent

3,734,876, was suggested as an alternative to

radiation-induced cross-linking in order to obtain more control over the product's properties and synthesis.

It would be advantageous if actinic radiation-curable polymer precursors based on

poly (oxyalkylene) glycols could be designed to lend mechanical strength to the solid polymeric electrolyte without loss of ionic conductivity.

Summary of the Invention

The strengthening of the so-called

poly(oxyalkylene) "soft sectors" in solid electrolyte polymer precursors is accomplished by linking blocks of poly(oxyalkylene) units, -(CH₂CHR¹O)_n-, with chemical linking groups to form a higher molecular weight

"macroglycol". Such linkages are:

In the present invention, more flexibility is introduced into the design of the macroglycol. While n may vary from about 2 to about 30 in each

poly(oxyalkylene) unit, because several units are linked to form a macroglycol, the preferred value of n is an integer in the range of from about 2 to about 10, more preferably from about 2 to about 5. R¹ is H or a C₁-C₃ alkyl group. R is a hydrocarbylene or

oxyhydrocarbylene group of from 1 to about 20 carbon atoms. R³ and R⁴ are C₁-C₆ hydrocarbyl groups.

The present invention is also directed, in part, to a solid electrolyte polymer precursor comprising an acryloyl-derivatized macroglycol; wherein the

macroglycol consists of poly(oxyalkylene) units,

-(CH₂CHR¹O)_n-, and/or blocks of polyester units

-(R⁶OC(O)R⁵C(O)O)_n-, linked by a chemical linking group selected from the group consisting of carbonate, phosphate, phosphonate, sulfone, siloxy and bis-carbonate, wherein n is preferably an integer from 1 to about 10.

In a particular embodiment, the invention is directed to a compound, finding use as a solid

electrolyte polymer precursor, which is represented by Formula I:

I A_k - Y - H_2-k wherein A represents Formula II and Y represents Formula III, and H is hydrogen:

II CH₂ = CHR²C(O)- III -O([Z_nX]_mZ_n[D[Z_nX]_mZ_n]_pD)_q[Z_nX]_mZ_n- wherein Z_n represents -(CH₂CHR¹O)_n- or -(R⁶OC(O)R⁵C(O)O)_n-; wherein D represents -C(O)NHR⁷NHC(O)O-; wherein X represents a chemical linking group selected from the group consisting of:

wherein said Formula I, k is 1 or 2; and wherein Formulas II and III; a is an integer from 1 to 10;

n is an integer from 1 to about 50; preferably from 2 to about 10; more preferably from 2 to about 5; m is an integer > 1; preferably from 1 to about 10;

p is O or an integer from 1 to about 20;

preferably from O to about 10;

q is O or an integer from 1 to 3;

R¹ is H, or C₁-C₃ alkyl;

R² is H, or C₁-C₆ alkyl; R³ and R⁴ are C₁-C₆

hydrocarbyl;

R⁶ is C₁-C₁₂ hydrocarbylene or oxyhydrocarbylene;

R⁷ and R⁵ are C₁-C₁₂ hydrocarbylene; and

R is a hydrocarbylene or oxyhydrocarbylene group of from 1 to 20 carbon atoms, preferably from 1 to about 7 carbon atoms.

Preferably Z is a (oxyalkylene) unit, more

preferably (oxyethylene), -(CH₂CH₂O)-, Z_n represents a block of poly(oxyalkylene) units, -(CH₂CHR¹O)_n-; Z_n also represents a block of polyester units

-(R⁶OC(O)R⁵C(O)O)_n-,

wherein R⁶ and R⁵ are hydrocarbylene groups derived from suitable diols and dicarboxylic acids respectively. For example, R⁶ is -CH₂CH₂- (ethylene glycol);

-(CH₂CH₂OCH₂CH₂)- (diethylene nxide glycol); -(CH₂)₄- (butylene glycol) and so forth. similarly, R⁵ is the hydrocarbylene portion of a suitable dibasic acid, such as glycolic acid, terephthalic acid and the like.

Preferably the isocyanate moiety denoted by D in Formula III, is a diisocyanate, and preferably R⁷ is phenylene, C₁-C₆ alkyl-substituted phenylene, C₂-C₆ alkylene, C₁₃-C₁₆ diphenylalkane, and the like, as derived, for example, from hexamethylene diisocyanate, isophorone diisocyanate, xylene diisocyanate, and alkyl-substituted xylene diisocyanate; or R⁷ may be derived from triiosocyanates such as biuret and

isocyanurate.

Preferably, the number average molecular weight of the polymer precursor is in the range of from about 200 to about 100,000, and more preferably is in the range of from about 1,000 to about 20,000, and most

preferably from about 4,000 to about 15,000.

Another aspect of the invention is a solid

electrolyte comprising a solid polymer matrix, solvent and an inorganic ion salt, wherein said polymer matrix is obtained by curing a polymer precursor represented by Formula I. Preferably actinic radiation is used to cure the polymer precursor.

Another aspect of this invention is an

electrochemical cell which comprises: an anode

comprising a compatible anodic material; a cathode comprising a compatible cathodic material; and

interposed therebetween, a solid electrolyte which comprises: a solid polymeric_ matrix; an inorganic ion salt; and a solvent; wherein said polymeric matrix is obtained by polymerizing a polymer precursor

represented by Formula I. In yet another aspect of the invention, an

electrochemical battery comprises a plurality of electrochemical cells as heretofore described.

Yet another aspect of the invention is a method of making a solid electrolyte which comprises the steps of forming a mixture comprising a solvent, an inorganic ion salt and a polymer precursor represented by

Formula I; and exposing said mixture to actinic

radiation.

Detailed Description of Preferred Embodiments

As noted above, this invention is directed to solid, single phase, solvent-containing polymeric electrolytes, and in particular, to polymer precursors which are employed to make the ion-conducting polymeric electrolyte. However, prior to describing this

invention in further detail, the following terms will first be defined.

Definitions

As used herein, the following terms have the following meanings.

The terms "solid, single phase polymeric

electrolyte" and "solid polymeric electrolyte" refer to an ionically conducting polymeric solid, normally comprising an inorganic ion salt, a compatible

electrolyte solvent, and a solid polymeric matrix.

The term "polymer precursor" refers to a prepolymer, which is itself of substantial molecular weight greater than 300 and preferably greater than 500, and which undergoes crosslinking reactions when "cured". The polymer precursor contains at least one hetero atom capable of forming donor-acceptor bonds with inorganic cations, for example, oxygen, sulfur or nitrogen with alkali metal cations.

Within the scope of the present invention, the polymer precursor is an acryloyl-derivatized, urethane oligomer of a macroglycol and diisocyanate.

The term "macroglycol" refers to particular high molecular weight polymer with hydroxyl end groups. The macroglycol consists of poly(oxyalkylene) groups or polyester groups linked together by linking groups, X, as previously defined. The molecular weight of the macroglycol is increased by increasing the number of poly(oxyalkylene) groups so linked by X, and by

optional further linking achieved by reacting the terminal hydroxy groups with a diisocyanate, or

triisocyanate, to produce urethane linkage. The macroglycol so-produced is reacted with diisocyanate and acrylic acid to provide the acrylate of Formula III. The number average molecular weight of the macroglycol ranges from about 200 to about 100,000, preferably from about 1,000 to about 50,000, more preferably from about 4,000 to about 15,000.

The term "salt" refers to any salt, for example, an inorganic salt, which is suitable for use in a solid electrolyte. Representative examples of suitable inorganic ion salts are alkali metal salts of less mobile anions of weak bases having a large anionic radius. Examples of such anions are I-, Br-, SCN-, ClO₄, BF-₄, PF-₆, AsF-₆, CF₃COO-, CF₃SO-₃ and the like. Specific examples of suitable inorganic ion salts include LiClO₄, Lil LiSCN, LiBF₄, LiAsF₆, LiCF₃SO₃, LiN(CF₃SO₃)₂, LiPF₆, NaSCN, KI, and the like. The inorganic ion salt preferably contains at least one atom selected from the group consisting of Li, Na and K.

The term "solid polymeric matrix" refers to an ionically conducting matrix formed by polymerizing an organic prepolymer, i.e. a polymer precursor containing at least one hetero atom capable of forming donor-acceptor bonds with inorganic cations derived from inorganic ion salts under conditions such that the resulting polymer is useful in preparing solid

polymeric electrolytes. Solid polymeric matrices are well known in the art and are described for example in U.S. Patent Nos. 4,908,283 and 4,925,751, both of which are incorporated herein by reference in their entirety.

The solid polymeric matrix of the present

invention is derived from the polymer precursor of the present invention by cross linking (curing) the

components of the polymer precursor. Such cross linking or curing is achieved chemically and is induced by thermal means or actinic radiation, preferably by actinic radiation. "Actinic radiation" refers to any radiation or particulate beam having the ability to induce the desired chemical reaction. Consequently, the actinic radiation is of an energy content which is appropriate to the desired reaction. In the practice of the present invention, the use of electron beam generators and ultraviolet light sources, well known to the art, produce actinic radiation of appropriate energy to cure an electrolyte mixture comprising a solid electrolyte polymer precursor.

The term "compatible electrolyte solvent", or in the context of components of the solid electrolyte, just "solvent", is a low molecular weight plasticizer added to the electrolyte and/or the cathode composition in which may also serve the purpose of solubilizing the inorganic ion salt. The solvent is any compatible volatile aprotic relatively polar solvent. Preferably, these materials have boiling points greater than about 80°C to simplify manufacture and increase the shelf life of the electrolyte/battery. Typical examples of solvent are mixtures of such materials as propylene carbonate, ethylene carbonate, gamma-butyrolactone anhydrous tetrahydrofuran, glyme, di-glyme, tri-glyme, tetraglyme, dimethyl-sulfoxide, dioxolane, sulfolane and the like. A particularly preferred solvent is disclosed in U.S. patent application Serial No.

07/918,438, filed July 22, 1992, which application is incorporated herein by reference in its entirety.

In the practice of the present invention, the macroglycol encompasses polyester groups of the formula -(R⁶OC(O)R⁵C(O)O)_n- and/or poly(oxyalkylene) units of the formula, -(CH₂CHR¹O)_n-, bonded together by a chemical linking group. The chemical linking reaction is carried out in an excess of glycol to assure that the macroglycol is hydroxyl group terminated. In a

preferred embodiment of the invention, the macroglycol is represented by Formula IV:

IV HO[Z_nX]_mZ_nH wherein Z_n and m have been defined previously.

The number average molecular weight of the

preferred macroglycol falls in the range of from about 300 to about 20,000, preferably from about 1,000 to about 5,000, corresponding to m being an integer from 1 to about 10, when n has an integral value from 2 to about 10.

The term "chemical linking group", X, refers to a chemical group (i.e. at least a di-radical) capable of reacting with to form a macroglycol as herein defined. In the practice of the present invention, the chemical linking group is selected from the group consisting of:

In the siloxy linking group, a is an integer from 1 to 10.

The urethane oligomer is produced by the reaction of the macroglycol with an isocyanate. In a preferred embodiment, the isocyanate is represented by the formula OCNR⁷NCO, where R⁷ is a C₁-C₁₂ hydrocarbylene. Any suitable isocyanate may be used, but typical isocyanates are hexamethylene diisocyanate, toluene 2,4- and 2,6- diisocyanate, naphthalene-1,5- di-isocyanate, methylene-4,4^,-di-phenyl diisocyanate and the like, well known to the art from their extensive use in polyurethane production.

In a preferred embodiment of the invention, the urethane oligomer is represented by Formula III,

III -O([Z_nX]_mZ_n[D[Z_nX]_mZ_n]_pD)_q[Z_nX]_mZ_n-

Where X and Z_n have been heretofore defined, and -D- is the isocyanate moiety-C(O)NHR⁷NHC(O)O-, where R⁷ has heretofore been defined, p is an integer from 0 to about 10, and q has a value from 1 to 3, indicating at least one urethane bond (q=1).

The term "acryloyl-derivatized" refers to a molecule containing the acryloyl-group, herein

represented by A, in Formula I: A_k-Y-H_2-k. For purposes of the present invention, the preferred acryloyl-group has the chemical formula CH₂=CR²C(O) -, wherein R² is H or a C₁-C₆ alkyl. The preferred acryloyl-derivatized urethane-oligomer is represented by Formula I, A_k-Y-H_2-k, where A is the aforementioned acryloyl group, Y is the aforementioned urethane oligomer, and H is hydrogen.

The acryloyl group is appended to the molecule to provide sites for crosslinking of the polymer precursor to other molecules in the electrolyte, thereby creating a solid polymeric matrix, k is the integer 1 or 2, representing mono- or di-acrylated urethane oligomer. The presence of urethane in the polymer precursor is optional, but the polymer precursor is always acryloyl-derivatized as heretofore described. In the absence of urethane bonds, the preferred polymer precursor is represented by the Formula V:

V A_kO[Z_nX]_mZ_nH_2-k

Formula IV represents an acryloyl-derivatized macroglycol wherein k, n and m have the values

heretofore defined.

The term "hydrocarbyl" and "hydrocarbylene" refer to monovalent and divalent organic radicals composed of carbon and hydrogen which may be aliphatic, alicyclic, aromatic or combinations thereof, e.g. aralkyl.

Examples of hydrocarbylene groups include alkylene such as ethylene, propylene, and the like, arylene such as phenylene, naphthalene, and the like, hydrocarbyl groups include alkyl, such as methyl, ethyl, propyl, butyl, isobutyl, pentyl, hexyl, heptyl, octyl and the like, alkenyls such as propenyl, isobutenyl, hexenyl, octenyl and the like, aryl such as phenyl, alkylphenyl including 4-methylphenyl, 4-ethylphenyl and the like, likewise, oxyhydrocarbyl refers to hydrocarbyl radicals containing minor amounts of unreactive oxygen, such as alkoxy, e.g. ethoxyethyl, propoxyethyl and the like.

The term "electrochemical cell" refers to a composite structure containing an anode, a cathode, and an ion-conducting electrolyte interposed therebetween.

The "anode" refers to an electrode for the half-cell reaction of oxidation on discharge which is typically comprised of a compatible anodic material i.e. any material which functions as an anode in a solid electrochemical cell. Such compatible anodic materials are well known in the art and include, by way of example, lithium, lithium alloys, such as alloys of lithium with aluminum, mercury, iron, zinc and the like, and intercalation based anodes such as carbon, tungsten oxides, intercalation-based anodes and the like.

The "cathode" refers to the counter-electrode to the anode and is typically comprised of a compatible cathodic material (i.e. insertion compounds) which is any material which functions as a cathode in an

electrochemical cell. Such compatible cathodic

materials are well known to the art and include, by way of example, manganese oxides, molybdenum oxides, vanadium oxides such as V₆O₁₃, lithiated cobalt oxides, lithiated nickel oxides sulfides of molybdenum, titanium and niobium, chromium oxides, copper oxides and the like. The particular compatible cathodic material employed is not critical. Methodology

Methods for preparing the solid polymeric matrix and solid electrolyte are well known in the art. The present invention however, utilizes a particular polymer precursor in the preparation of the solid polymeric matrix. The polymer precursor is an

acryloyl-derivatized oligomer of a macroglycol wherein the macroglycol is itself the reaction product of a glycol and a source of a linking group which serves to link polyester or poly (oxyalkylene) units, which are hydroxy-terminated, i.e., glycols.

Considering first the macroglycols, they are readily prepared as follows.

The macroglycol based on the linking of glycols by carbonate or bis-carbonate groups are prepared by reacting phosgene C(O)Cl₂ or bis-chloroformate

ClC(O)OROC(O)Cl, with an excess amount of glycol in a suitable solvent at moderate temperatures. Organic solvents such as chlorobenzene, 1,2-dichloroethane, anhydrous tetrahydrofuran, anisole and dioxane are used. The organic solvent prevents the loss of

phosgene by hydrolysis and precipitation of the polymer before it has the desired molecular weight. Reaction temperatures in the range of 0°-50°C are used.

Reference is made to the standard methods well known to the art as disclosed in, for example, W.F. Christopher and D.W. Fox, "Polycarbonates", Reinhold, N.Y. (1962); and H. Schnell, "Chemistry and Physics of

Polycarbonate", Wiley-Interscience, N.Y. (1964); the disclosure of each is herein incorporated by reference in its entirety. The macroglycol based on the linking of glycols by phosphate or phosphonate groups are prepared by reacting phosphoric dichloride ester Cl₂P(O)R⁴, or phosphonic dichloride Cl₂P(O)R⁴ with an excess amount of glycol. Reference is made to methods known to the art as disclosed, for example, in Kriecheldorf et al., Macromol . Chem . Rapid . Commun ., 9:217 (1988); Percec et al., Angew. Makromol . Chem . , 80:143 (1979); Pretula et al., Macromol . Chem. , 191:671 (1990); the disclosure of each of which is herein incorporated by reference in its entirety.

The macroglycol based on the linking of glycol by sulfone is prepared by reacting hydrocarbyl disulfonic acid chloride (hydrocarbyl disulfonyl chloride), i.e. ClO₂SRSO₂Cl, wherein R is a hydrocarbylene group as heretofore defined, with an excess amount of glycol. The hydrocarbyl disulfonyl chloride is made from the action of thionyl chloride (SOCl₂) on the hydrocarbyl disulfonic acid HOS(O₂)RS(O₂)OH. In the reaction of the hydrocarbyl disulfonic acid chloride with the

macroglycol a small amount of lithium hydroxide is preferably added. Reference is made to known methods in the art of synthesis as disclosed, for example, by Gaylord (ed.), "Polyethers", Wiley-Interscience, N.Y. (1962); and P.W. Morgan, "Condensation Polymers: by Interfacial and Solution Methods", Wiley-Interscience, N.Y. (1965); the disclosure of each of which is

incorporated herein by reference in its entirety as if fully said forth herein in ipsis verbis .

The macroglycol based on the linking of glycol by siloxy groups is prepared by reacting dihydrocarbyldichlorosilane, R³ ₂SiCl₂, or

dialkoxydichlorosilane, (R³O)₂SiCl₂, wherein R³ is the oxyhydrocarboxyl or hydrocarbyl heretofore defined, under substantially anhydrous conditions with an excess amount of poly(oxyalkylene) glycol. Reference is made to known methods of organic synthesis as disclosed in, for example, Patel et al., J. Chem . Educ , 60:181 (1983); the disclosure of which is incorporated herein by reference in its entirety. Blockcopolymers of siloxane units (i.e., a > 1) and poly (oxyalkylene) or polyester units will also prove satisfactory

macroglycols in the practice of the present invention. Reference is made to European Patent Application

91101273.0, filed January 31, 1991, when a > 1.

The preparation of the urethane oligomer is based on the reaction of a diisocyanate with excess

macroglycol. It is preferably prepared by reacting macroglycol and diisocyanate in molar ratio of from about 1:0.9 to about 1:0.1 under moderate temperature conditions, near ambient and usually no higher than 100°C. Significantly higher temperatures are avoided to prevent degradation. Reference is made to known methods in the art of polymer synthesis as disclosed in, for example, J.K. Backus et al., "Polyurethanes", in the "Encyclopedia of Polymer Science and

Engineering", 13:243-303 (1988); C.E. Schildknecht (ed.), "Polymerization Processes", Wiley-Interscience, N.Y. (1977); J.H. Saunders et al., "Polyurethane:

Chemistry and Technology", Wiley-Interscience, N.Y., Part I (1962), Part II, (1964); Phillips et al., "Polyurethanes, Chemistry, Technology and Properties", Gordon and Breach, N.Y. (1964); the disclosure of each of which is incorporated by reference in its entirety as if fully set forth herein in ipsis verbis .

It is within the scope of this invention to include a small proportion of diamine, such as ethylene diamine, in a step reaction, if the proportions of macroglycol and diisocyanate are reversed in the initial step herein above. That is, if macroglycol is first reacted with excess diisocyanate, then the product is then reacted with diamine and diisocyanate in a second step, and then a final step comprising the reaction of the product of the second step with

diisocyanate and excess macroglycol results in a blockcopolymer of "hard segments" and "soft segments" as is well known in the art of polyurethane

manufacturer referenced herein above.

The preparation of the acryloyl-derivatized urethane polymer precursor or of the acryloyl-derivatized polymer precursor, is based on the reaction of the urethane prepolymer, or the macroglycol, with acrylic acid. The prepolymeric materials are hydroxy-terminated and react directly with acrylic acid under esterification conditions to produce an acrylate-terminated polymer precursor.

The solid electrolyte and the electrochemical cell are prepared as described in the following example wherein the urethane acrylate, commercially available, is the polymer precursor for a polymeric solid matrix analogous to that of the present invention. While the urethane acrylate of the following example is not based upon a macroglycol as herein defined, the preparation of a solid electrolyte using a macroglycol-based polymer precursor is substantially the same.

Example

A solid electrolytic cell is prepared by first preparing a cathodic paste which is spread onto a current collector and is then cured to provide for the cathode. An electrolyte solution is then placed onto the cathode surface and is cured to provide for the solid electrolyte composition. Then, the anode is laminated onto the solid electrolyte composition to provide for a solid electrolytic cell. The specifics of this construction are as follows:

A. The Current Collector

The current collector employed is a sheet of aluminum foil having a layer of adhesion promoter attached to the surface of the foil which will contact the cathode so as to form a composite having a sheet of aluminum foil, a cathode and a layer of adhesion promoter interposed therebetween.

Specifically, the adhesion promoter layer is prepared as a dispersed colloidal solution in one of two methods. The first preparation of this colloidal solution for this example is as follows:

84.4 weight percent of carbon powder

(Shawinigan Black™ ╌ available from Chevron Chemical Company, San Ramon, CA)

337.6 weight percent of a 25 weight percent

solution of polyacrylic acid (a reported average molecular weight of about 90,000, commercially available from Aldrich Chemical Company ╌ contains about 84.4 grams polyacrylic acid and 253.2 grams water) 578.0 weight percent of isopropanol

The carbon powder and isopropanol are combined with mixing in a conventional high shear colloid mill mixer (Ebenbach-type colloid mill) until the carbon is uniformly dispersed and the carbon particle size is smaller than 10 microns. At this point, the 25 weight percent solution of polyacrylic acid is added to the solution and mixed for approximately 15 minutes. The resulting mixture is pumped to the coating head and roll coated with a Meyer rod onto a sheet of aluminum foil (about 9 inches wide and about 0.0005 inches thick). After application, the solution/foil are contacted with a Mylar wipe (about 0.002 inches thick by about 2 inches and by about 9 inches wide ╌ the entire width of aluminum foil). The wipe is flexibly engaged with the foil (i.e., the wipe merely contacted the foil) to redistribute the solution so as to provide for a substantially uniform coating. Evaporation of the solvents (i.e., water and isopropanol) via a conventional gas-fired oven provides for an

electrically-conducting adhesion-promoter layer of about 6 microns in thickness or about 3 × 10^-4 grams per cm². The aluminum foil is then cut to about 8 inches wide by removing approximately ½ inch from either side by the use of a conventional slitter so as to remove any uneven edges.

In order to further remove the protic solvent from this layer, the foil is redried. In particular, the foil is wound up and a copper support placed through the roll's cavity. The roll is then hung overnight from the support in a vacuum oven maintained at about 130°C. Afterwards, the roll is removed. In order to avoid absorption of moisture from the atmosphere, the roll is preferably stored into a desiccator or other similar anhydrous environment to minimize atmospheric moisture content until the cathode paste is ready for application onto this roll.

The second preparation of this colloidal solution comprises mixing 25 lbs of carbon powder (Shawinigan Black™ ╌ available from Chevron Chemical Company, San Ramon, CA) with 100 lbs of a 25 weight percent solution of polyacrylic acid (average molecular weight of about 240,000, commercially available from BF Goodrich, Cleveland, Ohio, as Good-Rite K702 ╌ contains about 25 lbs polyacrylic acid and 75 lbs water) and with 18.5 lbs of isopropanol. Stirring is done in a 30 gallon polyethylene drum with a gear-motor mixer (e.g.,

Lightin Labmaster Mixer, model XJ-43, available from Cole-Parmer Instruments Co., Niles, Illinois) at 720 rpm with two 5 inch diameter A310-type propellers mounted on a single shaft. This wets down the carbon and eliminates any further dust problem. The resulting weight of the mixture is 143.5 lbs and contains some "lumps".

The mixture is then further mixed with an ink mill which consists of three steel rollers almost in contact with each other, turning at 275, 300, and 325 rpms respectively. This high shear operation allows

particles that are sufficiently small to pass directly through the rollers. Those that do not pass through the rollers continue to mix in the ink mill until they are small enough to pass through these rollers. When the mixing is complete, the carbon powder is completely dispersed. A Hegman fineness of grind gauge (available from Paul N. Gardner Co., Pompano Beach, FL) indicates that the particles are 4-6 μm with the occasional

12.5 μm particles. The mixture can be stored for well over 1 month without the carbon settling out or

reagglomerating.

When this composition is to be used to coat the current collector, an additional 55.5 lbs of

isopropanol is mixed into the composition working with 5 gallon batches in a plastic pail using an air powered shaft mixer (Dayton model 42231 available from Granger Supply Co., San Jose, CA) with a 4 inch diameter Jiffy-Mixer brand impeller (such as an impeller available as Catalog No. G-04541-20 from Cole Parmer Instrument Co., Niles, Illinois). Then, it is gear pumped through a 25 μm cloth filter (e.g., So-Clean Filter Systems,

American Felt and Filter Company, Newburgh, NY) and Meyer-rod coated as described above.

B. The Cathode

The cathode is prepared from a cathodic paste which, in turn, is prepared from a cathode powder as follows: i. Cathode Powder

The cathode powder is prepared by combining 90.44 weight percent V₆O₁₃ [prepared by heating ammonium metavanadate (NH₄ ⁺VO₃-) at 450°C for 16 hours under N₂ flow] and 9.56 weight percent of carbon (from Chevron Chemical Company, San Ramon, CA under the tradename of Shawinigan Black™). About 100 grams of the resulting mixture is placed into a grinding machine (Attritor Model S-l purchased from Union Process, Akron, Ohio) and ground for 30 minutes. Afterwards, the resulting mixture is dried at about 260°C for 21 hours. ii. Cathode Paste

A cathode paste is prepared by combining

sufficient cathode powder to provide for a final product having 45 weight percent V₆O₁₃.

Specifically, 171.6 grams of a 4:1 weight ratio of propylene carbonate:triglyme is combined with

42.9 grams of polyethylene glycol diacrylate (molecular weight about 400 available as SR-344 from Sartomer Company, Inc., Exton, PA), and about 7.6 grams of ethoxylated trimethylolpropane triacylate (TMPEOTA) (molecular weight about 450 available as SR-454 from Sartomer Company, Inc., Exton, PA) in a double

planetary mixer (Ross #2 mixer available from Charles Ross & Sons, Company, Hauppag, New York).

A propeller mixture is inserted into the double planetary mixer and the resulting mixture is stirred at a 150 rpms until homogeneous. The resulting solution is then passed through sodiated 4A molecular sieves. The solution is then returned to double planetary mixer equipped with the propeller mixer and about 5 grams of polyethylene oxide (number average molecular weight about 600,000 available as Polyox WSR-205 from Union Carbide Chemicals and Plastics, Danbury, CT) is added to the solution vortex from by the propeller by a mini-sieve such as a 25 mesh mini-sieve commercially available as Order No. 57333-965 from VWR Scientific, San Francisco, CA.

The solution is then heated while stirring until the temperature of the solution reaches 65°C. At this point, stirring is continued until the solution is completely clear. The propeller blade is removed and the carbon powder prepared as above is then is added as well as an additional 28.71 grams of unground carbon (from Chevron Chemical Company, San Ramon, CA under the tradename of Shawinigan Black™). The resulting mixture is mixed at a rate of 7.5 cycles per second for 30 minutes in the double planetary mixer. During this mixing the temperature is slowly increased to a maximum of 73°C. At this point, the mixing is reduced to 1 cycle per second the mixture slowly cooled to 40°C to 48°C (e.g. about 45°C). The resulting cathode paste is maintained at this temperature until just prior to application onto the current collector.

The resulting cathode paste has the following approximate weight percent of components:

In an alternative embodiment, the requisite amounts of all of the solid components are added to directly to combined liquid components. In this regard, mixing speeds can be adjusted to account for the amount of the material mixed and size of vessel used to prepare the cathode paste. Such adjustments are well known to the skilled artisan.

In order to enhance the coatability of the carbon paste onto the current collector, it may be desirable to heat the paste to a temperature of from about 60°C to about 130°C and more preferably, from about 80°C to about 90°C and for a period of time of from about 0.1 to about 2 hours, more preferably, from about 0.1 to 1 hour and even more preferably from about 0.2 to 1 hour. A particularly preferred combination is to heat the paste at from about 80°C to about 90°C for about 0.33 to about 0.5 hours.

During this heating step, there is no need to stir or mix the paste although such stirring or mixing may be conducted during this step. However, the only requirement is that the composition be heated during this period. In this regard, the composition to be heated has a volume to surface area ratio such that the entire mass is heated during the heating step.

A further description of this heating step is set forth in U.S. Patent Application Serial No. 07/968,203 filed October 29, 1992 as Attorney Docket No. 1116 and entitled "METHODS FOR ENHANCING THE COATABILITY OF CARBON PASTES TO SUBSTRATES", which application is incorporated herein by reference in its entirety.

The so-prepared cathode paste is then placed onto the adhesion layer of the current collector described above by extrusion at a temperature of from about 45° to about 48°C. A Mylar cover sheet is then placed over the paste and the paste is spread to thickness of about 90 microns (μm) with a conventional plate and roller system and is cured by continuously passing the sheet through an electron beam apparatus (Electro-curtain, Energy Science Inc., Woburn, MA) at a voltage of about 175 kV and a current of about 1.0 Ma and at a rate of about 1 cm/sec. After curing, the Mylar sheet is removed to provide for a solid cathode laminated to the aluminum current collector described above.

C. Electrolyte

56.51 grams of propylene carbonate, 14.13 grams of triglyme, and 17.56 grams of urethane acrylate

(Photomer 6140, available from Henkel Corp., Coating and Chemical Division, Ambler, PA) are combined at room temperature until homogeneous. The resulting solution is passed through a column of 4A sodiated molecular sieves to remove water and then mixed at room

temperature until homogeneous.

At this point, 2.57 grams of polyethylene oxide film forming agent having a number average molecular weight of about 600,000 (available as Polyox WSR-205 from Union Carbide Chemicals and Plastics, Danbury, CT) is added to the solution and then dispersed while stirring with a magnetic stirrer over a period of about 120 minutes. After dispersion, the solution is heated to between 60°C and 65°C with stirring until the film forming agent dissolved. The solution is cooled to a temperature of between 45° and 48°C, a thermocouple is placed at the edge of the vortex created by the magnetic stirrer to monitor solution temperature, and then 9.24 grams of LiPF₆ is added to the solution over a 120 minute period while thoroughly mixing to ensure a substantially uniform temperature profile throughout the solution. Cooling is applied as necessary to maintain the temperature of the solution between 45° and 48°C.

In one embodiment, the polyethylene oxide film forming agent is added to the solution via a mini-sieve such as a 25 mesh mini-sieve commercially available as Order No. 57333-965 from VWR Scientific, San Francisco, CA.

The resulting solution contains the following:

This solution is then degassed to provide for an electrolyte solution wherein little, if any, of the LiPF₆ salt decomposes.

Optionally, solutions produced as above and which contains the prepolymer, the polyalkylene oxide film forming agent, the electrolyte solvent and the LiPF₆ salt are filtered to remove any solid particles or gels remaining in the solution. One suitable filter device is a sintered stainless steel screen having a pore size between 1 and 50 μm at 100% efficiency.

Alternatively, the electrolyte solution can be prepared in the following manner. Specifically, in this example, the mixing procedure is conducted using the following weight percent of components:

The mixing procedure employs the following steps:

1. Check the moisture level of the urethane acrylate. If the moisture level is less than 100 ppm water, proceed to step 2. If not, then first dissolve the urethane acrylate at room temperature, <30°C, in the propylene carbonate and triglyme and dry the solution over sodiated 4A molecular sieves (Grade 514, 8-12 Mesh from Schoofs Inc., Moraga, CA) and then proceed to step 4. 2. Dry the propylene carbonate and triglyme over sodiated 4A molecular sieves (Grade 514, 8-12 Mesh from Schoofs Inc., Moraga, CA).

3. At room temperature, <30°C, add the urethane acrylate to the solvent prepared in step 2. Stir at 300 rpm until the resin is completely dissolved. The solution should be clear and colorless.

4. Dry and then sift the polyethylene oxide film forming agent through a 25 mesh mini-sieve commercially available as Order No. 57333-965 from VWR Scientific, San Francisco, CA. While stirring at 300 rpm, add the dried and pre-sifted polyethylene oxide film forming agent slowing to the solution. The polyethylene oxide film forming agent should be sifted into the center of the vortex formed by the stirring means over a 30 minute period. Addition of the polyethylene oxide film forming agent should be dispersive and, during

addition, the temperature should be maintained at room temperature (<30°C).

5. After final addition of the polyethylene oxide film forming agent, stir an additional 30 minutes to ensure that the film forming agent is substantially dispersed.

6. Heat the mixture to 68°C to 75°C and stir until the film forming agent has melted and the solution has become transparent to light yellow in color.

Optionally, in this step, the mixture is heated to 65°C to 68°C. 7. Cool the solution produced in step 6 and when the temperature of the solution reaches 40°C, add the LiPF₆ salt very slowly making sure that the maximum temperature does not exceed 55°C.

8. After the final addition of the LiPF₆ salt, stir for an additional 30 minutes, degas, and let sit overnight and cool.

9. Filter the solution through a sintered

stainless steel screen having a pore size between 1 and 50 μm at 100% efficiency.

At all times, the temperature of the solution should be monitored with a thermocouple which should be placed in the vortex formed by the mixer.

Afterwards, the electrolyte mixture is then coated by a conventional knife blade to a thickness of about 50 μm onto the surface of the cathode sheet prepared as above (on the side opposite that of the current

collector) but without the Mylar covering. The

electrolyte is then cured by continuously passing the sheet through an electron beam apparatus

(Electrocurtain, Energy Science Inc., Woburn, MA) at a voltage of about 175 Kv and a current of about 1.0 Ma and at a conveyor speed setting of 50 which provides for a conveyor speed of about 1 cm/sec. After curing, a composite is recovered which contained a solid electrolyte laminated to a solid cathode. D . Anode

The anode comprises a sheet of lithium foil (about 51 μm thick) which is commercially available

from FMC Corporation Lithium Division, Bessemer City, North Carolina.

E. The Solid Electrolytic Cell

A sheet comprising a solid battery is prepared by laminating the lithium foil anode to the surface of the electrolyte in the sheet produced in step C above.

Lamination is accomplished by minimal pressure.

Claims

What Is Claimed Is:

1. A solid electrolyte polymer precursor, comprising an acrylolyl-derivatized macroglycol composed of blocks of poly(oxyalkylene) units,

-(CH₂CHR¹O)_n-, and/or blocks of polyester units

- (R⁶OC (O) R⁵C (O) O) _n-, linked by a chemical linking group selected from the group consisting of

wherein n is an integer from 1 to about 50;

R¹ is H or C₁-C₃ alkyl; R³ and R⁴ are C₁-C₆

hydrocarbyl;

R⁶ is a C₁-C₁₂ hydrocarbylene or oxyhydrocarbylene group;

R⁵ is a C₁-C₁₂ hydrocarbylene group; and

R is a hydrocarbylene or oxyhyrocarbylene group of from 1 to 20 carbon atoms.

2. A solid electrolyte polymer precursor

represented by Formula I:

I A_kY-H_2-k wherein k is 1 or 2 ; A represents Formula II,

H₂=CHR²C(O)-; and Y represents Formula III,

III -O{[Z_nX]_mZ_n[D[Z_nX]_mZ_n]_pD)_q[Z_nX]_mZ_n- wherein Z„ represents - (CH₂CHR¹O)_n-, or

-(R⁶OC(O)R⁵C(O)O)_n-; wherein D represents -C(O)NHR⁷NHC(O)O-; and wherein X represents a chemical linking group selected from the group consisting of:

wherein said Formulas II and III, a is an integer from 1 to 10;

n is an integer from 2 to about 10;

m is an integer > 1;

p is O or an integer from 1 to about 20;

q is O or an integer from 1 to 3;

R¹ is H, or C₁-C₃ alkyl;

R² is H, or C₁-C₆ alkyl;

R³ and R⁴ are C₁-C₆ are hydrocarbyl;

R⁶ is C₁-C₁₂ hydrocarbylene or

oxyhydrocarbylene;

R⁷ and R⁵ and C₁-C₁₂ hydrocarbylene; and

R is a hydrocarbylene or oxyhydrocarbylene of from 1 to 20 carbon atoms.

3. A solid electrolyte polymer precursor according to claim 2 wherein m is an integer between 1 and 10; p is O or an integer from 1 to 10; q is O or 1; R' is H or methyl and R¹ is H.

4. A solid electrolyte polymer precursor according to claim 3 wherein n is an integer from 2 to about 5.

5. A solid electrolyte polymer precursor according to claim 3 wherein q is O.

6. A solid electrolyte polymer precursor according to claim 2 wherein said chemical linking group is carbonate.

7. A solid electrolyte polymer precursor according to claim 2 wherein said chemical linking group is bicarbonate.

8. A solid electrolyte polymer precursor according to claim 2 wherein said chemical linking group is phosphate.

9. A solid electrolyte polymer precursor according to claim 2 wherein said chemical linking group is phosphonate.

10. A solid electrolyte polymer precursor

according to claim 2 wherein said chemical linking group is sulfone.

11. A solid electrolyte polymer precursor

according to claim 2 wherein said chemical linking group is siloxy.

12. A solid electrolyte polymer precursor

according to claim 1 wherein the molecular weight of said polymer precursor is in the range of from about 1,000 to about 20,000.

13. A solid electrolyte polymer according to claim 2 wherein the molecular weight of said polymer is in the range from about 1,000 to about 20,000.

14. A solid electrolyte comprising:

a solid polymer matrix;

a solvent; and

an inorganic ion salt;

wherein said polymer matrix is the product obtained by curing the solid electrolyte polymer precursor of claim 1.

15. A solid electrolyte comprising:

a solid polymeric matrix;

a solvent; and

an inorganic ion salt;

wherein said polymer matrix is the product obtained by curing the solid electrolyte polymer precursor of claim 2.

16. A solid electrolyte according to claim 14 wherein said curing is performed by exposure of the polymer precursor to actinic radiation.

17. A solid electrolyte according to claim 15 wherein said curing is performed by exposure of the polymer precursor too actinic radiation.

18. An electrochemical cell comprising: an anode composed of a compatible anodic material;

a cathode composed of a compatible cathodic material; and

the solid electrolyte of claim 14 interposed between said cathode and said anode.

19. An electrochemical cell comprising:

an anode composed of a compatible anodic material;

a cathode composed of a compatible cathodic material; and

the solid electrolyte of claim 15 interposed between said cathode and said anode.

20. A battery comprising at least two cells of claim 18.

21. A battery comprising at least two cells of claim 19.

22. A method of making a solid electrolyte

comprising the steps of forming a mixture of a

compatible solvent, an inorganic ion salt and the polymer precursor of claim 1; and exposing said mixture to actinic radiation.