WO2009146340A1

WO2009146340A1 - Polymer electrolyte materials based on polysiloxanes

Info

Publication number: WO2009146340A1
Application number: PCT/US2009/045356
Authority: WO
Inventors: Bing Hsieh; Mohit Singh
Original assignee: Seeo, Inc
Priority date: 2008-05-28
Filing date: 2009-05-27
Publication date: 2009-12-03

Abstract

A polymer with a siloxane backbone and oligoethylene oxide-containing pendant groups is disclosed. The pendant groups are linked to the backbone through a silicon-containing group. These siloxane-based polymers can be combined with salts, such as lithium salts, to create ionically conductive materials for use in batteries and the like.

Description

POLYMER ELECTROLYTE MATERIALS BASED ON POLYSILOXANES

Inventors: Bing R. Hsieh, Mohit Singh

BACKGROUND OF THE INVENTION Field of the Invention

[0001] This invention relates generally to high ionic conductivity polymer electrolytes, and, more specifically, to high ionic conductivity polymer electrolytes containing a new class of polysiloxanes having ethylene oxide pendant groups.

[0002] All publications referred to herein are incorporated by reference in their entirety for all purposes as if fully set forth herein.

[0003] The increased demand for lithium secondary batteries has resulted in research and development to improve their safety and performance. Many batteries employ liquid electrolytes and are associated with high degrees of volatility, flammability, and chemical reactivity. With this in mind, the idea of using a solid electrolyte with a lithium-based battery system has attracted great interest. While polyethylene oxide is a sufficiently conductive material as a liquid, its conductivity in solid form is too low to be practical for many applications. A variety of polysiloxane-based electrolytes have been developed to address these issues. Examples include polysiloxane materials that contain pendant oligomeric ethylene oxide groups prepared from poly(methylhydrosiloxanes), wherein the starting polymethylhydrosiloxane reacts with a vinyl or hydroxyl oligomeric ethylene oxide in the presence of a catalyst to produce the electrolyte. Although these materials offer good ionic conductivity, many are not solid at battery operating temperatures. Work continues to try to find ways to optimize material properties to find ways to solidify these materials while retaining their good ion conductivity.

[0004] H. Allcock et al., (29 Macromol. 7544-7552 (1996)) have proposed polyphosphazenes bearing branched and linear oligoethyleneoxy side groups as solid solvents for ionic conduction. However, certain properties of these materials led them to be less than optimal for use in connection with lithium batteries.

[0005] Highly conducting polymer electrolytes based on polysiloxanes have been disclosed by West, et al. U.S. Patent Number 6,337,383 discloses solid polysiloxane polymers with multiple oligooxyethylene side chains per silicon. The multiple oligooxyethylene side chains are each connected directly to the silicons, or they can be linked by a branching structure and then jointly linked to the silicons.

[0006] In U.S. Patent Publication Number 2004/0248014, West et al. disclose an electrolyte that includes a polysiloxane having one or more backbone silicons linked to a first side chain and one or more backbone silicons linked to a second side chain. The first side chains include a poly(alkylene oxide) moiety and the second side chains include a cyclic carbonate moiety.

[0007] In U.S. Patent Publication Number 2004/0214090, West et al. disclose a cyclic siloxane polymer electrolyte having poly(siloxane-g-ethylene oxides) with one or more poly(ethylene oxide) side chains directly bonded to Si atoms.

[0008] In U.S. Patent Number 6,887,619, West et al. disclose cross-linked polysiloxane polymers having oligooxyethylene side chains. Lithium salts of these polymers can be synthesized as a liquid and then caused to solidify in the presence of elevated temperatures to provide a solid electrolyte useful in lithium batteries.

[0009] In U.S. Patent Publication Number 2005/0170254, West et al. disclose disiloxanes that include a backbone with a first silicon and a second silicon. The first silicon is linked to a first substituent selected from a group consisting of: a first side chain that includes a cyclic carbonate moiety; a first side chain that includes a poly(alkylene oxide) moiety; and a first cross link links the disiloxane to a second siloxane and that includes a poly(alkylene oxide) moiety. The second silicon can be linked to a second substituent selected from a group consisting of: a second side chain that includes a cyclic carbonate moiety, and a second side chain that includes a poly(alkylene oxide) moiety.

[0010] U.S. Patent Publication Number 2006/0035154 discloses an electrolyte that includes one or more tetrasiloxanes. The tetrasiloxanes have a backbone with two central silicons and two terminal silicons. A first one of the silicons is linked to a side chain that includes a poly(alkylene oxide) moiety. A second one of the silicons is linked to a side chain that includes a poly(alkylene oxide) moiety or to a side chain that includes a cyclic carbonate moiety. When each of the central silicons is linked to a side chain that includes a poly(alkylene oxide) moiety, each of the central silicons is directly linked to the poly(alkylene oxide) moiety. [0011] Some of the West copolymers are polysiloxane materials that contain pendant oligomeric ethylene oxide groups prepared mainly from poly(methylhydrosiloxanes), as exemplified in the following scheme, wherein the starting polymethylhydrosiloxane reacts with a vinyl or hydroxyl oligomeric ethylene oxide in the presence of a catalyst to give the electrolyte products:

poly(methylhydrosiloxane)

[0012] These polysiloxane-based electrolytes typically have good ionic conductivity. Nevertheless, there is a still a need for yet more polymer electrolytes with high ionic conductivity and good material properties.

DETAILED DESCRIPTION

[0013] The embodiments of the present invention relate to siloxane-based polymers that can be combined with salts (e.g., lithium salts) to create ionically conductive materials for use in batteries and the like.

[0014] The preferred embodiments are illustrated in the context of polymer electrolytes in lithium batteries. The skilled artisan will readily appreciate, however, that the materials and methods disclosed herein will have application in a number of other contexts where conductive polymers are desirable, particularly where side chain flexibility is important.

[0015] In one embodiment of the invention, a molecule that has a polysiloxane backbone to which pendant groups attach forms a novel polymer. The pendant groups have the structure:

The overall structure of the novel polymer is:

where R can be selected individually for each siloxane repeat unit in the backbone and m is an integer ranging from about 2 to 2000. In some arrangements, there are some siloxane repeat units in the backbone where structure (1) is absent. R can be an oligoethylene-oxide- containing group. R can also be a highly polar group, such as an ethylene carbonate, cyano groups, N-pyrrolidone groups, or perfluoroalkyl group. In one arrangement, the polymer is a homopolymer when only one R moiety is used for all repeat units. In another arrangement, the polymer is a random copolymer with only two different R (Rl, R2) moieties distributed randomly among the repeat units. In another arrangement, the polymer is a random terpolymer with only three different R (R₁, R₂, R₃) moieties distributed randomly among the repeat units. In yet another arrangement, there can be any number of different R moieties attached randomly to the repeat units.

[0016] The polymer structures described above can be represented by the following formulas:

homopolymer

random copolymer

random terpolymer

where integers m, n, o can each have any value between about 2 and 2000. In another arrangement, m, n, o can each have any value between about 10 and 1000.

[0017] In one embodiment of the invention, a siloxane backbone is capped on each end by a trimethylsilyl group. Such a structure is represented by:

As has been discussed above, suitable R groups include, but are not limited to, oligoethylene- oxide-containing groups, ethylene carbonates, cyano groups, N-pyrrolidone groups, and perfluoroalkyl groups, and m is an integer ranging from about 2 to 2000.

[0018] In another embodiment of the invention, a siloxane backbone is capped on each end by a group that is identical to the pendant group. Such a structure is represented by:

As has been discussed above, suitable R groups include, but are not limited to, oligoethylene- oxide-containing groups, ethylene carbonates, cyano groups, N-pyrrolidone groups, and perfluoroalkyl groups, and m is an integer ranging from about 2 to 2000. [0019] Examples of oligoethylene-oxide-containing groups that are suitable for R include, but are not limited to the following groups:

-0-(CH₂CH₂O)-CH₃

-(CH₂J₃O-(CH₂CH₂O)-CH₃ — OSi(CH₃)₂-(CH₂)₃O-(CH₂CH₂O)-CH₃

— OSi(CH₃)₂-OSi(CH₃)₂-(CH₂)₃O-(CH₂CH₂O)-CH₃

-0-(CH₂CH₂CH₂O)-CH₃

-(CH₂J₃O-(CH₂CH₂CH₂O)-CH₃

— OSi(CH₃)₂-(CH₂)₃O-(CH₂CH₂CH₂O)_rCH₃

— OSi(CH₃)₂-OSi(CH₃)₂-(CH₂)₃O-(CH₂CH₂CH₂O)_rCH₃

— 0-(CH₂CH₂O)J- (CH₂CH₂CH₂O)J-CH₃ — OSi(CH₃)2-OSi(CH₃)₂-OSi(CH₃)₂-(CH₂)₃O-(CH₂CH₂O)_rCH₃

wherein i is an integer in the range of about 1 to 8. In one arrangement, j is also an integer in the range of about 1 to 8

[0020] Other oligoethylene-oxide-containing groups that are suitable for R include, but are not limited to some that contain double ethylene oxide strains such as:

wherein X can be, but is not limited to:

— OSi(CH₃)₂-(CH₂CH₂)-

-(CH₂CH₂)-

— (CH₂)₃OCH₂- ;

— OSi(CH₃)₂-(CH₂)₃OCH₂-

and wherein i is an integer in the range of about 1 to 8. [0021] Examples of ethylene-carbonate-containing groups that are suitable for R include, but are not limited to the following groups:

-\> wherein X can be, but is not limited to:

-OSi(CH₃J₂-(CH₂CH₂)-

-(CH₂CH₂)-

-(CH₂J₃OCH₂-

-OSi(CH3)₂-(CH2)₃OCH₂-

-OCH₂

-OCH₂CH₂-

[0022] Examples of cyano groups that are suitable for R include, but are not limited to the following groups:

-(CH₂)_n-CN

wherein n is an integer in the range of about 1 to 10.

[0023] Examples of N-pyrrolidone groups that are suitable for R include, but are not limited to the following:

wherein n is an integer in the range of aboutl to 8. [0024] Examples of perfluroalkyl groups that are suitable for R include, but are not limited to the following:

-(CH₂)_m(CF₂)_n-F

wherein m and n are integers that are selected independently and are in the range of about 1 to 8.

[0025] In one embodiment of the invention, the polysiloxane chain is represented by:

wherein n is an integer ranging from about 1 to 100.

[0026] In another embodiment of the invention, the polysiloxane chain is represented by:

wherein n is an integer ranging from about 1 to 100.

[0027] In yet another embodiment of the invention, the polysiloxane chain is represented by:

wherein n is an integer ranging from about 1 to 100. [0028] The new class of polysiloxane polymers described herein can be used as electrolytes in electrochemical devices. In one embodiment of the invention, an electrolyte is made by combining the novel polysiloxane polymers with a lithium salt. Lithium salts that can be used in the polymers described herein are not limited, as long as they aid lithium ion conduction in the polymer so it can be used as an electrolyte. Examples of specific lithium salts include LiSCN, LiN(CN)₂, LiClO₄, LiBF₄, LiAsF₆, LiPF₆, LiCF₃SO₃, Li(CF₃SO₂)₂N, Li(CF₃SO₂)₃C, LiN(SO₂C₂Fs)₂, lithium alkyl fluorophosphates, lithium oxalatoborate, as well as other lithium bis(chelato)borates having five to seven membered rings, LiPF₃(C₂Fs)₃, LiPF₃(CF₃)₃, LiB(C₂O₄)₂, and mixtures thereof. In other embodiments of the invention, for other electrochemistries, electrolytes are made by combining the novel polysiloxane polymers with various kinds of salts. Examples include, but are not limited to AgSO₃CF₃, NaSCN, NaSO₃CF₃, KTFSI, NaTFSI, Ba(TFSI)₂, Pb(TFSI)₂, and Ca(TFSI)₂.

[0029] Polysiloxane electrolytes, as disclosed herein, are more ionically conducting than many other polymer electrolytes that have been employed in batteries. It is known that polymers with flexible backbone chains generally have higher ionic conductivity than do polymers with stiff backbone chains. In addition to having a flexible silane backbone chain, the polymers disclosed herein have very flexible silicon-containing side chains. Without wishing to be bound to any particular theory, it may be that the increased flexibility of the side chains increases the ionic conductivity of the polymer further than is possible with stiffer side chain groups.

[0030] The basic method of making the novel polymers can be described generally as allowing a poly(methylvinylsiloxane) to undergo a hydrosilylation reaction with hydrosilane compound(s) in the presence of a metal catalyst. In one embodiment of the invention, a platinum catalyst such as chloroplatinic acid and platinum divinyltetramethyl disiloxane complex (also known as the Karstedt's catalyst), platinum cyclovinylmethylsiloxane complex, or platinum octanal/octanol complex is used.

[0031] Examples of processes for synthesizing polysiloxane polymers with particular R groups are given below. The examples are meant to be illustrative and not limiting.

Example 1

[0032] A three-neck round flask was equipped with a magnetic stirrer, two addition funnels, a nitrogen inlet, and a rubber septum. Sodium hydride (60% dispersion in mineral oil) (46 g, 1.15 mol) and then inhibitor free tetrahydrofuran (Aldrich 439215) (500 ml) were added into the flask. Triethylene glycol monomethyl ether (156 ml, 0.976 mol) and allyl bromide (100 ml, 1.155 mol) were placed separately into each of the two addition funnels to await addition into the flask. The mixture was then cooled with an ice- water bath before the triethylene glycol monomethyl ether was added dropwise from the funnel into the flask. The resulting mixture was stirred at room temperature for at least two hours. The mixture was cooled again with an ice-water bath before the allyl bromide was added from the funnel into the flask dropwise. The resulting mixture was stirred overnight at room temperature. The solid (mostly NaBr) that had formed in the mixture was removed by suction filtration. The solid was rinsed with tetrahydrofuran. The filtrate was concentrated in vacuo (rotavap followed by pump under vacuum) and then vacuum distilled (80-90⁰C) to give triethylene glycol allyl methyl ether (structure shown below) as a colorless liquid (169 g, 89%).

(2)

[0033] A flask was equipped with a magnetic stirrer and an addition funnel. 1,1,3,3- tetramethydisiloxane (250 g, 1.86 mol) and toluene (150 ml) were added into the flask. Triethylene glycol allyl methyl ether (2) (40.8 g, 0.2 mol), toluene (50 ml), and platinum divinyltetramethyldisilane catalyst (2.1-2.4% platinum concentration) (12 drops) were placed in the addition funnel to await addition into the flask. The disiloxane solution was heated to 60-70⁰C, before adding the triethylene glycol allyl methyl ether solution dropwise. Five hours later, an additional six drops of Pt catalyst were added. The resulting solution was heated for a total of 24 hours, cooled, and then concentrated in vacuo (rotavap followed by pump under vacuum). The resulting liquid was fractionally distilled under vacuum (bath temperature 130⁰C and pressure of 0.2-0.8 mm Hg) to give the following fractions: first fraction: 50-93⁰C (unwanted unknown materials); second fraction: >95°C, (mostly desired product). The second fraction was redistilled (0.4 mmHg) and the fraction between 100- 125°C was collected and identified as the desired silane product with the following structure:

[0034] Poly(vinylmethylsiloxane) (molecular weight of 1000 to 1500 from Gelest) (0.78 g, 0.011 mol vinyl groups), the silane product from (3) above (3.95g, 0.011 mol), toluene (5 ml) and platinum divinyltetramethyl disiloxane complex in xylene (2.1 - 2.4% Pt from Gelest) (3 drops) were mixed together. The resulting solution was heated at 60-70⁰C for 16 hours and then cooled. Solvent was evaporated from the solution followed by vacuum drying for 48 hours to give a lightly colored viscous oil (4.5 g) with the following structure (Polymer I):

Example 2

[0035] Into a 250 ml round flask equipped with a magnetic stirrer and a drierite tube was added Methylene glycol monomethyl ether (10.2 g, 0.05 mol), chlorodimethylsilane (7.0 g, 0.074 mol), toluene (60 ml), and platinum divinyltetramethyldisilane catalyst (2.1-2.4% platinum concentration) (6 drops). The solution was heated at 60-70⁰C for 24 h and then cooled. Solvent was evaporated and the residual material was pumped under vacuum overnight to give a crude product (13.9 g) that contained mostly a compound of the following structure as verified by NMR:

Compound (5) was reduced by 1 M LiAlH^ether (50 ml) by stirring at room temperature overnight. Water was added to decompose the excess LiAlH₄, and the resulting mixture was extracted with hexane, followed by workup to give a lightly colored liquid which was fractionally distilled under vaccum. Four fractions were obtained at different temperature intervals and characterized by NMR. The third fraction (3.4 g) was identified as the desired product with the following structure:

[0036] Poly(vinylmethylsiloxane) (molecular weight of 1000 to 1500 from Gelest) (0.78 g, 0.011 mol vinyl groups), and the silane product (6) (3.1g, 0.012 mol), toluene (5 ml) and platinum divinyltetramethyl disiloxane complex in xylene (2.1 - 2.4% Pt from Gelest) (3 drops) were mixed together. The resulting solution was heated at 60-70⁰C for 24 h and then cooled. Solvent was evaporated followed by vacuum drying for 48 h to give a lightly colored viscous oil with the following structure (Polymer II):

Example 3

[0037] Into a IL round flask equipped with a magnetic stirrer, a drierite tube, and an addition funnel was added Methylene glycol monomethyl ether (16.4 g, 0.1 mol), hexane (180 ml), triethylamine (18 ml). The resulting solution was cooled with an ice water bath. Chlorodimethylsilane (11.0 g, 0.116 mol) was added into the addition funnel and was then added dropwise into the cooled solution of Methylene glycol monomethyl ether toluene. The resulting mixture was stirred for 30 min at 0⁰C and then suction filtered. The filtrate was concentrated in vacuo and the residual oil was fraction distilled under vacuum (60-70°C/0.3 mmHg) to give a colorless oil (15.1 g, 68%) with the following structure:

[0038] Poly(vinylmethylsiloxane) (molecular weight of 1000 to 1500 from Gelest) (2.34 g, 0.033 mol vinyl groups), the silane product (8) (7.8 g), toluene (15 ml), and platinum divinyltetramethyl disiloxane complex in xylene (2.1 - 2.4% Pt from Gelest) (5 drops) were mixed together. The resulting solution was heated at 60-70⁰C for 24 h and then cooled. Solvent was evaporated followed by vacuum drying for 48 h to give a lightly colored viscous oil with the following structure (Polymer III):

Example 4

[0039] For ionic conductivity measurements, the polymers were first dried in the antechamber of a glovebox at 120⁰C overnight. A sample of a given [Li]/[EO] ratio (R value) was then prepared by mixing the polymer with an appropriate amount of lithium bis(trifluorosulfonyl)imide (LiTFSI) to give the corresponding polymer electrolyte. A piece of circular polypropylene mesh (OD =7/8", 200 micron thick, 34% porosity) was dipped into the electrolyte sample and then placed in a spring loaded stainless steel Swagelok cell. The ionic conductivities of the electrolytes were extracted from AC impedance curves measured at room temperature (RT) and at 8O⁰C (500kHz to 500 mHz, and voltage amplitude of 50 mV). The very high ionic conductivities of electrolytes made from Polymer I, Polymer II, and Polymer III are summarized in the following table.

[0040] This invention has been described herein in considerable detail to provide those skilled in the art with information relevant to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by different equipment, materials and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the scope of the invention itself.

Claims

We Claim:

1. A polymer having a siloxane backbone and the following structure:

wherein R is individually selected for each siloxane repeat unit in the backbone, R is selected from the group consisting of oligoethylene-oxide-containing groups, highly polar groups, ethylene carbonates, cyano groups, N-pyrrolidone groups, and perfluoroalkyl groups, and m is an integer ranging from about 2 to 2000.

2. The polymer of Claim 1, wherein the oligoethylene-oxide-containing group is selected from the group consisting of:

-0-(CH₂CH₂O)_nCH₃

— (CH₂)₃O-(CH₂CH₂O)_rCH₃

— OSi(CH₃)₂-(CH₂)₃O-(CH₂CH₂O)_rCH₃

— OSi(CH₃)₂-OSi(CH₃)₂-(CH₂)₃O-(CH₂CH₂O)_rCH₃

-0-(CH₂CH₂CH₂O)_nCH₃

— (CH₂)₃O-(CH₂CH₂CH₂O)_rCH₃

— OSi(CH₃)₂-(CH₂)₃O-(CH₂CH₂CH₂O)_rCH₃

— OSi(CH₃)₂-OSi(CH₃)₂-(CH₂)₃O-(CH₂CH₂CH₂O)-CH₃

-0-(CH₂CH₂O)-(CH₂CH₂CH₂O)-CH_{3 and} — OSi(CH₃)2-OSi(CH₃)₂-OSi(CH₃)₂-(CH₂)₃O-(CH₂CH₂O)_rCH₃ wherein i is an integer in the range of about 1 to 8 and:

wherein X is selected from the group consisting of: — OSi(CH₃)₂-(CH₂CH₂)-

-(CH₂CH₂)-

— (CH₂J₃OCH₂- ; and

— OSi(CH₃)₂-(CH₂)₃OCH₂-

and wherein i is an integer in the range of about 1 to 8.

3. The polymer of Claim 1, wherein the ethylene carbonates are selected from the group consisting of:

wherein X is selected from the group consisting of: -OSi(CH₃J₂-(CH₂CH₂)-

-(CH₂CH₂)-

-(CH₂J₃OCH₂-

-OSi(CH3)₂-( CH₂J₃OCH₂-

-OCH_j and

-OCH₂CH₂-

4. The polymer of Claim 1, wherein the cyano groups are selected from the group consisting of:

-(CH₂)_n-CN

wherein n is an integer in the range of about 1 to 10.

5. The polymer of Claim 1, wherein the N-pyrrolidone group comprises:

wherein n is an integer in the range of about 1 to 8.

6. The polymer of Claim 1, wherein the perfluroalkyl group comprises:

-(CH₂)_m(CF₂)_n-F wherein m and n are integers that are selected independently and are each in the range of about 1 to 8.

7. The polymer of Claim 1, wherein only one R group is included in the polymer.

8. The polymer of Claim 1, wherein only two different R groups are included in the polymer.

9. The polymer of Claim 1, wherein only three different R groups are included in the polymer.

10. The polymer of Claim 1, further comprising a methyl group at each end of the siloxane backbone.

11. The polymer of Claim 1, further comprising a

CH₃

R-Si — group at each end of the siloxane backbone. CH₃

12. A polymer comprising the structure:

wherein m is an integer ranging from about 2 to 2000 and Ri is selected from the group consisting of oligoethylene-oxide-containing groups, highly polar groups, ethylene carbonates, cyano groups, N-pyrrolidone groups, and perfluoroalkyl groups.

13. The polymer of Claim 12 wherein Ri comprises:

14. The polymer of Claim 12 wherein Ri comprises:

15. The polymer of Claim 12 wherein Ri comprises:

16. The polymer of Claim 12 wherein Ri comprises:

and X is selected from the group consisting of

— OSi(CH₃)2-(CH₂CH2)- ; -(CH₂CH₂)- ; -CH₂O-

17. A random copolymer comprising the structure:

wherein m is an integer ranging from 1 to 1000, n is an integer ranging from 1 to 1000 and Ri and R₂ are each selected independently from the group consisting of oligoethylene-oxide-containing groups, highly polar groups, ethylene carbonates, cyano, N-pyrrolidone groups, and perfluoroalkyl groups.

18. A random terpolymer comprising the structure:

CH₃ — Si — CH₃ CH₃; — Si — CH₃ CH₃ — Si — CH₃ R-I R₂ R₃ wherein m is an integer ranging from 1 to 1000, n is an integer ranging from 1 to 1000, o is an integer ranging from 1 to 1000 and R₁, R₂, and R₃ are each selected independently from the group consisting of oligoethylene-oxide-containing groups, highly polar groups, ethylene carbonates, cyano groups, N-pyrrolidone groups, and perfluoroalkyl groups.

19. An electrochemical device, comprising an electrolyte wherein the electrolyte comprises a polymer according to Claim 1 and a salt.

20. The device of Claim 19 wherein the salt is selected from the group consisting of AgSO₃CF₃, NaSCN, NaSO₃CF₃, KTFSI, NaTFSI, Ba(TFSI)₂, Pb(TFSI)₂, and Ca(TFSI)₂.

21. The device of Claim 19 wherein the salt comprises lithium.

22. The device of Claim 21 wherein the salt is selected from the group consisting of LiSCN, LiN(CN)₂, LiClO₄, LiBF₄, LiAsF₆, LiPF₆, LiCF₃SO₃, Li(CF₃SO₂)₂N, Li(CF₃SO₂)₃C, LiN(SO₂C₂Fs)₂), lithium alkyl fluorophosphates, lithium oxalatoborate, as well as other lithium bis(chelato)borates having five to seven membered rings, LiPF₃(C₂Fs)₃, LiPF₃(CF₃)₃, LiB(C₂O₄)₂, and mixtures thereof.

23. The device of Claim 19, wherein only one type of R group is included in the polymer.

24. The device of Claim 19, wherein only two different types of R groups are included in the polymer.

25. The device of Claim 19, wherein only three different types of R groups are included in the polymer.

26. The device of Claim 19, further comprising a methyl group at each end of the polysiloxane backbone.

27. The device of Claim 19 wherein the polysiloxane chain is represented by:

wherein n is an integer ranging from about 1 to 100. 28. The device of Claim 19 wherein the polysiloxane chain is represented by:

wherein n is an integer ranging from about 1 to 100.

9. The device of Claim 19 wherein the polysiloxane chain is represented by:

wherein n is an integer ranging from about 1 to 100.