TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Preparation Details : The salt concentration in the polyether film is preferably nil, and the films comprising the negative and positive electrodes and electrolyte have thicknesses between 10 and 150 mu . The polyether comprises units -O-CH2-CHR(derived from an oxiran CH2CHR-O) in which R is 1 - 16C alkyl, or from units -O-CH2CHR'-(from an oxiran CH2-CHR'-O) in which R' is a group capable of radical polymerisation, more preferred groups being vinyl, allyl, vinylbenzyl or acryloly. The material composite forming the positive electrode comprises an active material, binder a material conferring electronic conductivity and the Li salt.The active material may be Li1+xV3O8(x less than 4), LixV2O5,nH2O(x less than 3, n less than 2), LiFePO4, phosphates and sulfates of Fe or vanadyl, derivatives of LiMn2O4 or LiMnO2,derivatives of LiCoO2 or LiNiO2. The negative electrode comprises a film of Li, or a composite material comprising an active material, binder, an electronic conductor and a Li salt.The active material is either a carbonaceous compound, an alloy with Li of type LixM(M = Sn, Sb or Si) or compounds LixCu6Sn5( x is less than 13), iron borates, pnictures, oxides with reversible decomposition or insertion oxides such as titanates, MoO3 and WO3. The Li salt is chosen from LiPF6, LiAsF6, LiClO4, LiBF4, LiC4BO8, Li(C2F5SO2)2N, Li((C2F5)PF3), LiCF3SO3, LiCH3SO3 and LiN(SO2CF3)2. The binder is a non-solvating polymer and an aprotic compound, or a solvating polymer ; the aprotic compound is a carbonate, ether, ester, sulfone, sulfamide or nitrile, and the polymer is a homo- or copolymer of vinylidine fluoride, copolymers of ethylene, propylene and a diene, , homo and copolymers of tetrafluoroethylene, N-vinyl-pyrrolidone, acrylonitrile polymers or homo- and copolymers of methacrylonitrile.The polymer may comprise ionic functions. The solvating polymer is chosen from polyethers, copolymers of ethylene or propylene oxide or allylglycidylether, polyphosphazenes, polyethylene glycol cross-linked by isocyanates, oxyethylene and epichlorhydrin copolymers and cross-linkable polycondensates. The compound conferring electronic conduction is preferably carbon black. The composite also conais a non-volatile organic liquid from aprotic polar compounds such as carbonates, ethers etc., phthalates such as dioctyl phthalate, or polyethylene glycol. The polyether of the electrolyte film is a copolymer comprising cross-linked units, and at least one of the electrodes comprises a composite containing a cross-linking agent for the polyether. EXAMPLE - Preparation of a solid electrolyte battery : Separate preparations were carried out for the electrolyte film and a film for the positive electrode, the anode comprising a Li foil. The electrolyte film was of thickness 20 mu and comprises a copolymer of ethylene oxide, propylene oxide and allylglycidylether (94/4/2). The electrode film comprised a composite containing LiV3O8, carbon, and a mixture of PVDF/HFP(85/15) as binder, LiTFSI, as Li salt and Irganox . as antioxidant. Trials were effected with different amounts of the various constituents. ; for each trial, the cathode film, the POE film and the Li film were assembled by superimposing the films on a current collector then applying a pressure of 3 bar at 45 degrees C. Each was tested by cycling at 2 - 3.3 V with a discharged current of 0.7 mA/cm2 and charge current of 0.35 mA/cm2. The results obtained, in terms of power and cycling were similar to those obtained with batteries of similar constitution obtained from a POE film in which the Li salt was introduced before assembling.