TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The electrolyte further comprises a plasticizer comprising a carbonate or a mixture of carbonates comprising propylene carbonate, ethylene carbonate and dimethyl carbonate or succinonitrile and tetraethylsulfonamide. Preferred Components: The cell has an operating temperature of 60-100 degrees C. The positive electrode active material is lithium iron phosphate. The amount of positive electrode active material/cm2/face is higher than 0.6 mAh/cm2. The positive electrode further comprises an agent generating an electrical conductivity, and the di- or tri-copolymers. The weight ratio between the positive electrode active material, the solid polymer electrolyte and carbon is 60:32:8. Preferred Components: The block A includes 225-2250 ethylene oxide units. The block A has a molecular weight of 10-50 kDA. The vinyl monomers of the block B are lithium styrene-sulfonyl (trifluoromethylsulfonyl) imide (STFSILi), lithium sulfonyl (trifluoromethylsulfonyl)imide acrylate (ATFSILi), lithium sulfonyl(trifluoromethylsulfonyl)imide methacrylate (MMATFSILi), lithium sulfonyl(trifluoromethylsulfonyl) imide acrylamide, lithium sulfonyl(trifluoromethylsulfonyl)imide methacrylamide, lithium ethylene sulfonyl(trifluoromethylsulfonyl)imide, lithium propylene sulfonyl(trifluoromethylsulfonyl)imide, lithium dienesulfonyl(trifluoromethylsulfonyl)imide or lithium maleimidesulfonyl(trifluoromethylsulfonyl)imide. The block B is obtained from the copolymerization of the vinyl monomer and at least one monomer comprising styrene, acrylate, poly(ethylene glycol) or 1-16C-alkyl acrylate. The copolymers are (i) triblock copolymers of the type of poly(STFSILi)-b-polyethylene oxide (PEO)-b-poly(STFSILi) in which the ratio between poly(STFSILi) to PEO is 10-40 mass%, or (ii) triblock copolymers of the type poly(MMATFSILi-statistical-polyethylene glycol acrylate (APEG))-b-PEO-b-poly(MMATFSILi-statistical-APEG) in which the blocks B are statistical methacrylate copolymers of TFSILi and polyethylene glycol acrylate, and the ratio between P(MMATFSILi-stat-APEG) and PEO is 10-40 mass%. The copolymers are: poly(STFSILi)-b-PEO-b-poly(STFSILi), in which the blocks poly(STFSILi) have a number average molecular weight of 2000-7500 g/mole and the central block PEO has an average molecular weight of 35000 g/mole; poly(STFSILi)-b-POE-b-poly(STFSILi), in which poly(STFSILi) blocks have a number average molecular weight of 4900 g/mole and the central block of PEO has a molecular weight of 35000 g/mole, where the amount of block PEO is 78 mass% in total mass of copolymer; and poly(MMASTFSILi-statistical-APEG)-b-PEO-b-poly(MMATFSILi-statistical-APEG), where the block B are statistical copolymer of the TFSILi methacrylate and polyethylene glycol acrylate in which the block poly(MMATFSILi-statistical-APEG) has an average molecular weight of 7500 g/mole and the central block of PEO has an average molecular weight of 35000 g/mole, and the amount of block POE is 70% in the total mass of copolymer. EXAMPLE - No suitable example given.