Method for developing an electrochemical device
The invention relates to the development of an electrochemical device including a lithium salt/polyether electrolyte film between two films forming the cathode and the anode, respectively. The method of the invention involves assembling a multilayer structure consisting of the current-collecting carrier, the cathode-forming film, the electrolyte-forming polyether film and the anode-forming film. The cathode and/or anode films are made of a composite material containing the lithium salt. The polyether film is lithium salt-free. The assembled device is allowed to rest for long enough to enable the lithium salt in the cathode and/or the anode to be dispersed throughout the polymer film.
1. A process comprising:
providing a first film intended to form a positive electrode and a second film intended to form a negative electrode, where one or both of the films comprise a lithium salt;
providing an extruded polyether film which is not impregnated with a lithium salt;
assembling a multilayer structure comprising a current collecting support and the first and second films as electrodes and the extruded polyether film, which is not impregnated with a lithium salt, as an electrolyte; and
allowing diffusion of the lithium salt from one or both of the electrodes into the polyether film.
2. The process as claimed in claim 1 , wherein the films respectively constituting the negative electrode, the positive electrode and the electrolyte have thicknesses of between 10 μm and 150 μm.
3. The process as claimed in claim 1 , wherein the polyether is chosen from the copolymers which are obtained from ethylene oxide and from at least one substituted oxirane and which comprise at least 70% of —CH 2 —CH 2 O— repeat units derived from ethylene oxide.
4. The process as claimed in claim 3 , wherein the polyether comprises —O—CH 2 —CHR— units, derived from an oxirane CH 2 —CHR—O , in which R is an alkyl radical.
5. The process as claimed in claim 4 , wherein R is an alkyl radical having from 1 to 16 carbon atoms.
6. The process as claimed in claim 3 , wherein the polyether comprises —O—CH 2 CHR′— units, derived from an oxirane CH 2 —CHR′—O in which R′ is a group capable of polymerizing by the radical route.
7. The process as claimed in claim 6 , wherein said group capable of polymerizing by the radical route is selected from the group consisting of a vinyl, allyl, vinylbenzyl and acryloyl group.
8. The process as claimed in claim 3 , wherein the polyether comprises repeat units derived from several substituted oxiranes.
9. The process as claimed in claim 1 , wherein the composite material of the film intended to form the positive electrode comprises an active material, a binder, a material conferring electronic conductivity and the lithium salt.
10. The process as claimed in claim 9 , wherein the positive electrode active material is selected from the group consisting of Li 1+x V 3 O 8 , 0<x<4, Li x V 2 O 5 ·nH 2 O, 0<x<3, 0<n<2, LiFePO 4 , hydrated or anhydrous iron phosphates and sulfates, hydrated or anhydrous vanadyl phosphates and sulfates, LiMn 2 O 4 , the compounds derived from LiMn 2 O 4 obtained by partial substitution of Mn by Al, Ni and/or Co, LiMnO 2 , the compounds derived from LiMnO 2 obtained by partial substitution of Mn by Al, Ni and/or Co, LiCoO 2 , the compounds derived from LiCoO 2 obtained by partial substitution of Li by Al, Ti, Mg, Ni and/or Mn, LiNiO 2 and the compounds derived from LiNiO 2 obtained by partial substitution of Ni by Al, Ti, Mg and/or Mn.
11. The process as claimed in claim 1 , wherein the film constituting the negative electrode is a lithium film.
12. The process as claimed in claim 1 , wherein the film intended to form the negative electrode is composed of a composite material which comprises an active material, a binder, a material conferring electronic conductivity and the lithium salt.
13. The process as claimed in claim 12 , wherein the active material is selected from the group consisting of:
carbon compounds,
alloys with lithium of Li x M type (M=Sn, Sb, Si) (obtained from SnO, from SnO 2 , from Sn, Sn—Fe(—C) compounds, from Si compounds, from Sb compounds), and
Li x Cu 6 Sn 5 (0<x<13) compounds, iron borates, pnictides, simple oxides possessing reversible decomposition and insertion oxides, such as titanates, MoO 3 or WO 3 .
14. The process as claimed in claim 1 , wherein the lithium salt is selected from the group consisting of LiPF 6 , LiAsF 6 , LiClO 4 , LiBF 4 , LiC 4 BO 8 , Li(C 2 F 5 SO 2 ) 2 N, Li[(C 2 F 5 ) 3 PF 3 ], LiCF 3 SO 3 , LiCH 3 SO 3 and LiN(SO 2 CF 3 ) 2 .
15. The process as claimed in claim 9 , wherein the binder is composed either of a nonsolvating polymer and at least one polar aprotic compound, or of a solvating polymer.
16. The process as claimed in claim 15 , wherein the polar aprotic compound is selected from the group consisting of linear or cyclic carbonates, linear or cyclic ethers, linear or cyclic esters, linear or cyclic sulfones, sulfamides and nitriles.
17. The process as claimed in claim 15 , wherein the nonsolvating polymer is selected from the group consisting of:
vinylidene fluoride homopolymers and copolymers,
copolymers of ethylene, of propylene and of a diene,
tetrafluoroethylene homopolymers and copolymers,
N-vinylpyrrolidone homopolymers and copolymers,
acrylonitrile homopolymers and copolymers, and
methacrylonitrile homopolymers and copolymers.
18. The process as claimed in claim 15 , wherein the nonsolvating polymer carries ionic functional groups.
19. The process as claimed in claim 15 , wherein the binder is a solvating polymer selected from the group consisting of polyethers of linear, comb or block structure, forming or not forming a network, based on poly(ethylene oxide); copolymers comprising the ethylene oxide or propylene oxide or allyl glycidyl ether unit; polyphosphazenes; crosslinked networks based on polyethylene glycol crosslinked by isocyanates; copolymers of oxyethylene and of epichlorohydrin; and networks obtained by polycondensation which carry groups which make possible the incorporation of crosslinkable groups.
20. The process as claimed in claim 9 , wherein the compound conferring electronic conduction properties is preferably a carbon black which does not catalyze the oxidation of the electrolyte at high potential.
21. The process as claimed in claim 9 , wherein the composite material additionally comprises a nonvolatile liquid organic solvent.
22. The process as claimed in claim 21 , wherein said liquid solvent is selected from the group consisting of:
polar aprotic compounds, such as linear or cyclic carbonates, linear or cyclic ethers, linear or cyclic esters, linear or cyclic sulfones, sulfamides and nitriles,
phthalates, such as dioctyl phthalate, dibutyl phthalate and dimethyl phthalate, and
a polyethylene glycol or poly(ethylene glycol) dimethyl ether of low mass.
23. The process as claimed in claim 1 , wherein the polyether of the film intended to form the electrolyte is a copolymer comprising crosslinkable units and in that at least one of the electrodes is composed of a composite material which additionally comprises a crosslinking agent for said polyether.