COPOLYESTER FILMS FOR USE AS SEPARATORS IN METAL-ION BATTERIES

Abstract

A copolyester film comprising a copolyester which comprises repeating units derived from a diol, a dicarboxylic acid and a poly(alkylene oxide), wherein the copolyester film further comprises a first metal ion-containing component selected from conductive ceramic particulate materials, and wherein the film may further comprise additional metal ions from one or more sources other than said conductive ceramic particulate material.

Claims

1. A copolyester film comprising a copolyester which comprises repeating units derived from a diol, a dicarboxylic acid and a poly(alkylene oxide), wherein the copolyester film further comprises a first metal ion-containing component selected from conductive ceramic particulate materials, wherein said first metal ion-containing component is a lithium ion-containing component or a sodium ion-containing component, wherein the film may further comprise additional metal ions from one or more sources other than said conductive ceramic particulate material, and wherein, when present, the metal of said additional metal ions is the same as the metal of said first metal ion-containing component.

2. A film according to claim 1, wherein the film has a thickness of no more than 200 ?m, preferably no more than 150 ?m, preferably no more than 100 ?m, preferably no more than 85 ?m, preferably no more than 70 ?m, preferably no more than 50 ?m, and preferably no more than 35 ?m.

3. A film according to any preceding claim, wherein the film has a thickness of from 5 ?m, preferably from 10 ?m, preferably from 15 ?m, and preferably from 20 ?m.

4. A film according to any preceding claim, wherein said copolyester comprises semi-crystalline segments derived from an dicarboxylic acid and an aliphatic diol, and amorphous segments derived from poly(alkylene oxide).

5. A film according to any preceding claim wherein the poly(alkylene oxide) constitutes from 0.1 to 80 wt %, preferably from about 5 to about 78 wt %, preferably from about 10 to about 75 wt %, preferably from about 12 to about 65 wt %, preferably from about 15 to about 60 wt %, preferably from about 16 to about 55 wt % by total weight of the copolyester.

6. A film according to any preceding claim wherein the diol is selected from C.sub.2, C.sub.3 or C.sub.4 aliphatic diols, preferably wherein the aliphatic diol is ethylene glycol.

7. A film according to any preceding claim wherein the dicarboxylic acid is an aromatic dicarboxylic acid selected from isophthalic acid, naphthalene dicarboxylic acid and terephthalic acid.

8. A film according to any preceding claim wherein the poly(alkylene oxide)glycol is selected from C.sub.2 to C.sub.15, preferably C.sub.2 to C.sub.10, preferably C.sub.2 to C.sub.6 alkylene chains, preferably polyethylene glycol (PEG), polypropylene glycol (PPG) and poly(tetramethylene oxide) glycol (PTMO), preferably from PEG and PPG, preferably wherein the poly(alkylene oxide) is PEG.

9. A film according to any preceding claim wherein the number average molecular weight of the poly(alkylene oxide) is from about 200 to about 20000 g/mol, preferably from about 400 to about 3500 g/mol, preferably from about 500 to about 3500 g/mol.

10. A film according to any preceding claim wherein the film comprises said first metal ion-containing component and said additional metal ions.

11. A film according to any preceding claim, wherein said additional metal ions are in the form of a second metal ion component, preferably selected from metal salts.

12. A film according to any preceding claim, wherein said metal is lithium.

13. A film according to any preceding claim, wherein said metal is lithium and the lithium ion-containing conductive ceramic particulate material is selected from NASICON-type ceramic particulate materials such as lithium ion-containing conductive glass ceramic particulate materials; LISICON-type ceramic particulate materials; perovskite-type oxide ceramic particulate materials; garnet-type oxide ceramic particulate materials; lithium phosphorus oxynitride (LIPON)-type ceramic particulate materials; and lithium aluminium silicate (LAS) ceramic particulate materials.

14. A film according to any of claims 1 to 13, wherein said metal is lithium and the lithium ion-containing conductive ceramic particulate material is selected from: NASICON-type materials having the general formula LiM.sub.y(PO.sub.4).sub.3, where M denotes a multivalent metal ion such as one or more of Al, Si, Ti, Zr, Ge, Sn and Hf; NASICON-type materials having the general formula Li.sub.1+xM.sub.xTi.sub.2?x(PO.sub.4).sub.3 (LATP) where M denotes a trivalent cation selected from one or more of Al, Sc, Y and La; NASICON-type materials having the general formula Li.sub.1+xAl.sub.xGe.sub.2?x(PO.sub.4).sub.3 (LAGP); materials having a crystalline phase of Li.sub.1+x+yAl.sub.xTi.sub.2?xSi.sub.yP.sub.3?yO.sub.12 and a composition of Li.sub.2OAl.sub.2O.sub.3SiO.sub.2P.sub.2O.sub.5TiO.sub.2; materials having a main crystalline phase of Li.sub.1+x+yAl.sub.x(Ti,Ge).sub.2?xSi.sub.yP.sub.3?yO.sub.12 and a composition of Li.sub.2OAl.sub.2O.sub.3SiO.sub.2P.sub.2O.sub.5TiO.sub.2GeO.sub.2; LISICON-type materials having the general formula Li.sub.2+2xZn.sub.1?xGeO.sub.4, optionally wherein other elements (typically isovalent elements) may replace the Li, Zn and/or Ge, such as Li.sub.2+2xZn.sub.1?xGe.sub.4O.sub.16, Li.sub.14ZnGe.sub.4O.sub.16, Li.sub.(3+x)Ge.sub.xV.sub.(1?x)O.sub.4, Li.sub.(4?x)Si.sub.(1?x)P.sub.xO.sub.4; thio-LISICON-type materials such as Li.sub.(4?x)Ge.sub.(1?x)P.sub.xS.sub.4Li.sub.10GeP.sub.2S.sub.12; perovskite-type oxide materials such as Li.sub.3xLa.sub.(2/3)?xTiO.sub.3 (LLTO) and Li.sub.3xLa.sub.1/3?xTaO.sub.3; garnet-type oxide materials having the general formula Li.sub.7?3y?xLa.sub.3Zr.sub.2?xM1.sub.yM2.sub.xO.sub.12 (where M1 denotes a trivalent cation such as Al and Ga, M2 denotes a pentavalent cation such as Nb and Ta, x?0 and y?2) such as Li.sub.5La.sub.3M2O.sub.12 (where M denotes Nb and/or Ta), Li.sub.6ALa.sub.2M2O.sub.12 (where A denotes Ca, Sr and/or Ba, and M denotes Nb or Ta) or Li.sub.6.5La.sub.2.5Ba.sub.0.5ZrTaO.sub.12; LIPON-type materials having the general formula Li.sub.xPO.sub.yN.sub.z, such as Li.sub.2PO.sub.2N; and LAS-type materials such as AlLiO.sub.6Si.sub.2.

15. A film according to any of claims 1 to 11, wherein said metal is sodium and the sodium ion-containing conductive ceramic particulate material is selected from NASICON-type materials such as conductive glass ceramic particulate materials, beta-alumina and beta-alumina phases Na.sub.2O.Math.nAl.sub.2O.sub.3 where 5?n?11, sodium rare earth silicates, and sodium-ion conducting oxyhalide glasses; and preferably from NASICON-structured oxides having the general formula Na.sub.3Zr.sub.2Si.sub.2PO.sub.12, NaTi.sub.2(PO.sub.4).sub.3, NaGe.sub.2(PO.sub.4).sub.3 or Na.sub.1+x[Sn.sub.xGe.sub.2?x(PO.sub.4).sub.3], sodium rare earth silicates having the general formula Na.sub.5MSi.sub.4O.sub.12, where M is Y, Sc, Lu and/or any trivalent rare earth cation, and sodium-ion conducting oxyhalide glass such as NaINaClNa.sub.2OB.sub.2O.sub.3.

16. A film according to any preceding claim wherein the amount of said metal-ion containing conductive ceramic particulate material present in the copolyester film is in the range of from 0.1 wt % to 60 wt %, preferably from 5 wt % to 50 wt %, preferably from 8 wt % to 35 wt %, preferably from 10 to 20 wt % by total weight of the copolyester film.

17. A film according to any preceding claim wherein said additional metal ions are in the form of a metal salt selected from salts of: (i) aromatic carboxylic acids, preferably aromatic dicarboxylic acids, preferably terephthalic acid or isophthalic acid; (ii) aliphatic carboxylic acids, including aliphatic dicarboxylic acids, preferably acetic acid, glycolic acid or succinic acid; (iii) carbonic acids; (iv) phenolic acids, preferably salicylic acid; (v) mineral acids, such as perchloric acid or phosphoric acid, particularly phosphoric acid; and (vi) boric acids, preferably bis(oxalate)boric acid.

18. A film according to any preceding claim wherein said additional metal ions are in the form of a metal salt of an organic acid, and which is preferably the salt of the aromatic dicarboxylic acid from which the copolyester is derived.

19. A film according to claim 17 or 18 wherein said additional metal ions are in the form of a metal salt selected from the alkoxylate esters of said acids, preferably the carboxylic acids, preferably the dicarboxylic acids, preferably the aromatic dicarboxylic acids, preferably terephthalic acid, and wherein said alkoxylate esters are preferably derived from the aliphatic diols, preferably from C.sub.2-10 aliphatic diols, preferably from C.sub.2-6 aliphatic diols, preferably from C.sub.2, C.sub.3 or C.sub.4 aliphatic diols, more preferably from ethylene glycol, 1,3-propanediol and 1,4-butanediol, more preferably from ethylene glycol.

20. A film according to any preceding claim wherein said additional metal ions are lithium ions and in the form of lithium salts selected from bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF.sub.6), lithium tetrafluoroborate (LiBF.sub.4), lithium thiocyanate (LiSCN), lithium hexafluoroarsenate (LiAsF.sub.6), lithium trifluoromethanesulfonate (LiCF.sub.3SO.sub.3), lithium bromide (LiBr), lithium iodide (LiI), lithium bis(trifluoromethanesulfonimide) (LiN(CF.sub.3SO.sub.2).sub.2), lithium tris(trifluoromethylsulfonyl)methide (LiC(CF.sub.3SO.sub.2).sub.3), lithium orthosilicate, lithium trifluoroacetate (LiCF.sub.3CO.sub.2), lithium bis(fluorosulfite)amide (LiN(FO.sub.2S).sub.2), dilithium terephthalate (DLTA), dilithium isophthalate, lithium glycolate, lithium benzoate, lithium acetate, lithium carbonate, lithium perchlorate, lithium orthosilicate, lithium phosphate, lithium salicylate, lithium succinate, lithium bis(oxalato)borate and dilithium bis hydroxy ethyl terephthalate (DL-BHET).

21. A film according to any preceding claim wherein said additional metal ions are lithium ions and in the form of lithium salts selected from dilithium terephthalate (DLTA), dilithium isophthalate, dilithium bis hydroxy ethyl terephthalate (DL-BHET) and LiCF.sub.3SO.sub.3.

22. A film according to any of claims 1 to 18 wherein said additional metal ions are sodium ions and in the form of sodium salts selected from sodium nitrate (NaNO.sub.3), sodium perchlorate (NaClO.sub.4), sodium tetrafluoroborate (NaBF.sub.4), sodium hexafluorophosphate (NaPF.sub.6), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium bis(trifluoromethane)sulfonimide (Na[N(CF.sub.3SO.sub.2).sub.2]), sodium hexafluoroarsenate(V) (NaAsF.sub.6), sodium bis(oxalatoborate) (NaBOB), sodium halides (NaX), where X=Cl, Br or I, sodium thiocyanate (NaSCN), sodium pentacyanopropenide (NaPCPI), sodium tetracyanopirolate (NaTCP) and sodium tricyanoimidazolate (NaTIM).

23. A film according to any of claims 1 to 22 wherein said additional metal ions are present in and held within the polymeric matrix of the film by the interaction between the metal cations and negatively charged oxygen atoms of the copolyester, preferably at least the oxygen atoms of the polyalkylene oxide units.

24. A film according to any of claims 1 to 22 wherein said additional metal ions are in the form of a metal salt and held within the polymeric matrix of the film by virtue of the interaction between the metal cations and the anion of said metal salt which is not covalently bound to the copolyester.

25. A film according to any preceding claim wherein the amount of said additional metal ions in the film is effective to provide a metal:O molar ratio of from 5:1 to 1:50, preferably from about 4:1 to about 1:50, preferably from about 3:1 to about 1:50, preferably from about 2:1 to about 1:50, preferably about 1:1 to about 1:40, preferably about 1:2 to about 1:30, preferably about 1:4 to about 1:25, wherein the number of O atoms in this ratio is defined as the number of O atoms in the poly(alkylene oxide) residues, and the number of metal atoms in this ratio is defined as the number of metal atoms provided by said additional metal ions.

26. A film according to any preceding claim wherein said additional metal ions are in the form of a second metal ion component (preferably metal salts) which is present in an amount of from 0.1 wt % to 40 wt %, preferably from 1 wt % to 10 wt % by total weight of the copolyester film.

27. A film according to any preceding claim wherein the copolyester, first metal ion-containing component and, where present, a second metal ion component comprising said additional metal ions, are the major component of the film and preferably make up at least about 85%, preferably at least about 95%, and preferably at least about 98% by weight of the total weight of the copolyester film.

28. A film according to any preceding claim which further comprises an antioxidant.

29. A film according to any preceding claim which further comprises an inorganic particulate filler selected from metalloid oxides such as alumina, titania, zirconia, zinc oxide, talc and silica; calcined china clay; alkaline metal salts such as the carbonates and sulphates of calcium and barium; and non-conductive ceramic particulate materials, wherein said inorganic particulate filler is a different entity from the first and second metal ion-containing components and does not contain the metal ion of the first or second metal ion-containing components, preferably wherein the inorganic particulate filler is present in amounts of from 5 wt % to 20 wt %, by total weight of the copolyester film.

30. A film according to any preceding claim which exhibits a conductivity of at least about 10.sup.?7 S/cm, preferably of at least about 10.sup.?6 S/cm measured at 25? C., and/or a conductivity of at least about 10.sup.?6 S/cm, preferably at least about 10.sup.?5 S/cm measured at 60? C.

31. A film according to any preceding claim which is a self-supporting, biaxially oriented film.

32. A method of manufacturing a polyester film as described in any of claims 1 to 31, wherein said method comprises the comprises the steps of: (i) reacting said diol with said dicarboxylic acid or an ester thereof (suitably a lower alkyl (C.sub.1-4) ester, preferably the dimethyl ester), to form a bis(hydroxyalkyl)-ester of said dicarboxylic acid; (ii) polymerising in a polycondensation reaction said bis(hydroxyalkyl)-ester of said dicarboxylic acid in the presence of an poly(alkylene oxide) to form a copolyester; (iii) introducing said first metal ion-containing component selected from conductive ceramic particulate materials, and optionally said additional metal ions from one or more sources other than said conductive ceramic particulate materials, during synthesis of the copolyester in steps (i) and/or (ii), and/or during a subsequent separate compounding or mixing step, to form a copolyester composition; and (iv) forming a copolyester film from said copolyester composition, preferably by melt-extruding said composition or by solvent-casting a dispersion or solution comprising said copolyester composition.

33. A method of manufacturing a polyester film according to claim 32, wherein the reaction product of step (ii) is subjected to solid state polymerisation.

34. A method according to claim 32 or 33 wherein said film is cast on a supporting base which is itself a component of a solid state battery, preferably an electrode.

35. A film obtained by a method according to any one of claims 32 to 34.

36. A metal-ion battery comprising an anode, a cathode and a separator between the anode and the cathode, wherein said separator is the film defined in any of claims 1 to 31 or 35.

37. A metal-ion battery according to claim 36 wherein the metal-ion battery is a solid-state battery.

38. A metal-ion battery according to claim 36 or 37 wherein the metal of said metal-ion battery is selected from lithium.

39. A metal-ion battery according to claim 36, 37 or 38 wherein the anode is selected from graphite and lithium titanate (LTO) anodes, and/or wherein the cathode is made from lithium or mixed oxides of lithium and other metal(s), particularly lithium titanate, lithium iron phosphate (LiFePO.sub.4) and/or lithium-nickel-manganese-cobalt oxide (LiNiMnCoO.sub.2).

40. A metal-ion battery according to any of claims 36 to 39 wherein the metal-ion battery further comprises an anode current collector disposed on a surface of the anode and a cathode current collector disposed on the surface of the cathode, such that the layer order is anode current collector/anode/separator/cathode/cathode current collector.

41. A metal-ion battery according to any of claims 36 to 40, wherein said anode current collector and/or said cathode current collector are independently selected from current collectors comprising a biaxially oriented polyester substrate layer and a first metal layer on a side of the polyester substrate layer, wherein the polyester substrate layer exhibits positive thermal expansion in air at 200? C. in each of the transverse direction (TD) and machine direction (MD), wherein the polyester substrate layer has a thickness of no more than 12 ?m, and wherein the first metal layer has a thickness of from 50 to 1000 nm, and preferably wherein the current collector further comprises a second metal layer having a thickness of from 50 to 1000 nm wherein the first metal layer and the second metal layer are on opposing sides of the polyester substrate layer, preferably wherein the first metal layer and, where present, the second metal layer each independently comprise at least one of aluminium, copper, nickel, titanium, silver, nickel-copper alloy, or aluminium-zirconium alloy, and preferably wherein the first and second metal layers are selected from the same material, and preferably wherein the first and second metal layers are both either aluminium or copper.

42. Use of a film as defined in any of claims 1 to 31 or 35 as a separator in a metal-ion battery, preferably wherein said battery is as defined in any of claims 36 to 41.

43. A method of manufacturing a metal-ion battery as defined in any of claims 36 to 41 comprising a copolyester film defined in any of claims 1 to 31 or 35, the method comprising the steps of: (a) providing the copolyester film defined in any of claims 1 to 31 or 35; (b) assembling the metal-ion battery, wherein the battery comprises an anode, a cathode and a separator between the anode and the cathode, wherein said separator is the copolyester film obtained from step (a).

Description

EXAMPLES

[0162] In the following discussion, reference to LICGC is to a lithium-ion conducting glass ceramic powder available commercially from Ohara under the tradename LICGC? PW-01, and reference to PEG3350 is to a polyethylene glycol having a number average molecular weight (M.sub.N) of 3350.

Experiment 1

[0163] A copolyester (P1) was made using ethylene glycol, terephthalic acid and polyethylene glycol (PEG3350). PEG3350 was present at a level of 16.4 wt % of the copolyester.

[0164] The copolyesters were made by reacting 5551 g terephthalic acid, 2664 g ethylene glycol and 2006 g PEG3350 under pressure (about 40 psi) at high temperature (about 255? C.), along with the addition of an antioxidant (Irganox? 1010, 7 g). A trace of sodium hydroxide (0.35 g) was added to prevent the formation of unwanted by-products, and the esterification reaction proceeded without the need of a catalyst. Water was distilled off from the reaction and the reaction stopped once 90% of the theoretical weight of water from the reaction had been collected. An antifoam agent (Xiameter? DC 1510-US, 0.35 g) was then added to minimise material carryover. Polycondensation was then effected with a titanium-based catalyst system (Tyzor? TnBT, 2 g and Tyzor? AC422, 7.1 g) at about 275? C., and wherein the pressure above the melt was reduced to less than 1 mm Hg. As the polycondensation reaction proceeded, the viscosity of the batch increased, and once an appropriate viscosity (suitably from about 50 to about 100 Pa.Math.S) had been achieved the polymerisation reaction was stopped by restoring the pressure in the vessel back to atmosphere. The copolyester was then extruded as a lace and cast into a water bath, dried and pelletized.

[0165] A series of copolyester films based on copolyester P1 was made and comprising various additives, as shown in Table 1, which also shows the thickness, ionic conductivity, internal resistance (R.sub.1) and bulk resistance (R.sub.2) of the final film.

[0166] A film was prepared by melt-extruding and casting copolyester P1 to form a cast copolyester film, which was subsequently biaxially drawn using a simultaneous forward and sideways draw ratio of 3.5.

[0167] Comparative Example 3 and Example 1 were made by solvent casting techniques after dissolution/dispersion of the film of Comparative Example 2 in N-methyl-2-pyrrolidone (NMP). Specifically, the components shown in Table 1 were dispersed and thoroughly mixed in 5 mL NMP in an autoclave at 160? C. for 24 hours. The resultant copolyester composition was then cast on the surface of an aluminium disc (i.e. the electrode in the test cell) and dried by heating at 60? C. for 24 hours. The dried copolyester was then subjected to vacuum drying at 60? C. for 24 hours to provide the copolyester films.

[0168] A further comparative film (Comparative Example 1) comprising LICGC was obtained from Ohara under the tradename LICGC? AG-01.

TABLE-US-00001 TABLE 1 Film Ionic thickness conductivity R1 R2 Example Components (?m) (S/cm) (?) (?) Comparative LICGC 220 4.4 ? 10.sup.?5 10 1400 Example 1 Comparative P1 70 <1 ? 10.sup.?9 Example 2 Comparative P1 (0.3 g) 23 0.1 ? 10.sup.?5 18 1112 Example 3 LiCF.sub.3SO.sub.3 (0.2 g) Example 1 P1 (0.4 g) 32 0.9 ? 10.sup.?5 5 171 LiCF.sub.3SO.sub.3 (0.1 g) LICGC (0.3 g)

[0169] A comparison of Example 1 with Comparative Examples 2 and 3 demonstrates that the addition of the ceramic particle material significantly improves the ionic conductivity of the polyester films. Indeed, the film of Example 1 provides an ionic conductivity which is comparable to the ceramic separator of Comparative Example 1, with the advantage of being significantly thinner. Furthermore, the film of Example 1 demonstrated advantageous flexibility compared to Comparative Example 1 which was very brittle and thereby difficult to manufacture and subject to fracture in use. Thus, the film of Example 1 exhibited an advantageous combination of ionic conductivity, flexibility and low thickness for use as a separator in a solid state battery, whilst retaining ease of manufacture.

Experiment 2

[0170] The copolyester was made using bis(2-hydroxyethyl) isophthalate (BHEI) and polyethylene glycol (PEG 3350). PEG 3350 was present at a level of 50 wt % of the copolyester. The copolyesters were made by reacting 49.82 g BHEI, and 50.18 kg PEG 3350 along with the addition of an antioxidant (Irganox? 1010, 2.95 g). Polycondensation was effected with an antimony trioxide catalyst (0.20 g) at about 280-290? C., and wherein the pressure above the melt was reduced to less than 5 mm Hg. As the polycondensation reaction proceeded, the viscosity of the batch increased, and once a pre-determined viscosity had been achieved the polymerisation reaction was stopped by restoring the pressure in the vessel back to atmosphere. The copolyester was then extruded as a lace, cast into a water bath and dried.

[0171] Copolyester P2 was then used to prepare a series of solvent-cast copolyester films (Comparative Examples 4 and 5 and Example 2) containing various additives, as shown in Table 2. The copolyester was dissolved in NMP and the other components shown in Table 2 were introduced, dispersed and thoroughly mixed in NMP in a beaker at 25? C. for 12 hours. Comparative Example 4 used 10 mL NMP, Comparative Example 5 used 0.5 mL NMP whereas Example 2 used 5 mL NMP. Films were made by solvent-casting the resultant copolyester compositions on an aluminium surface and dried by heating at 60? C. for 24 hours, and then vacuum-dried at 60? C. for a further 24 hours to provide the copolyester film. Table 2 shows the thickness, ionic conductivity, internal resistance (R.sub.1) and bulk resistance (R.sub.2) of the final film.

TABLE-US-00002 TABLE 2 Film Ionic thickness conductivity R1 R2 Example Components (?m) (S/cm) (?) (?) Comparative LICGC 220 4.4 ? 10.sup.?5 10 1400 Example 1 Comparative P2 (0.5 g) 10 <1 ? 10.sup.?9 Example 4 Comparative P2 (0.8 g) 73 0.3 ? 10.sup.?5 22 1320 Example 5 LiCF.sub.3SO.sub.3 (0.2 g) Example 2 P2 (0.4 g) 82 0.5 ? 10.sup.?5 45 930 LiCF.sub.3SO.sub.3 (0.1 g) LICGC (0.5 g)

[0172] A comparison of Example 2 with Comparative Examples 4 and 5 demonstrates that the addition of the ceramic particulate material significantly improves the ionic conductivity of the polyester films. The separator of Example 2 provides an ionic conductivity which approaches that of the ceramic separator of Comparative Example 1, with the advantages of being significantly thinner and showing advantageous mechanical properties, in particular flexibility without brittleness.

Experiment 3

[0173] The ionic conductivity of the films of Comparative Examples 3 and 5, and Examples 1 and 2 was also measured at 40? C. and 60? C., and the results are shown in Table 3, along with the ionic conductivity at 25? C.

TABLE-US-00003 TABLE 3 Ionic Ionic Ionic conductivity conductivity conductivity (S/cm) at (S/cm) at (S/cm) at Example 25? C. 40? C. 60? C. Comparative Example 3 1.09 ? 10.sup.?6 7.87 ? 10.sup.?6 1.84 ? 10.sup.?5 Example 1 8.15 ? 10.sup.?6 2.98 ? 10.sup.?5 4.11 ? 10.sup.?5 Comparative Example 5 2.32 ? 10.sup.?6 1.04 ? 10.sup.?5 2.01 ? 10.sup.?5 Example 2 5.00 ? 10.sup.?6 2.19 ? 10.sup.?5 3.07 ? 10.sup.?5

[0174] The results in Table 3 demonstrate that the addition of the ceramic particle material significantly improves the ionic conductivity of the polyester films at all temperatures tested, and to commercially useful levels of ionic conductivity. Furthermore, the results in Table 3 demonstrate that ionic conductivity can be reliably increased even at elevated temperatures.