TECHNOLOGY FOCUS - POLYMERS - The copolymer is a block or graft copolymer, particularly a fluorinated copolymer with at least one of the segmented polymer chains (a) and (b) which are different and are homopolymer or copolymer of one or more vinyl fluoride, vinylidene fluoride, trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, chlorofluoroethylene, perfluorovinyl ether, 2,3,3,4,4,5,5-heptafluoropent-1-ene and monomers with polar group(s) in the side-chain, or copolymer of at least one of these monomers with ethylene and/or propylene.    TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - The lithium secondary batteries are prepared from a lithium salt chosen from ionizable lithium salts such as LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, Li(CF3SO2)2N, Li(CF3SO2)3C and LiSbF6; and a solvent selected from ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, gamma-butyrolactone, dimethoxyethane, diethoxyethane and their mixture. EXAMPLE - A block copolymer was prepared with segmented polymer chain (a) of homo(vinylidene fluoride), and segmented polymer chain (b) containing a copolymer of vinylidene fluoride/hexafluoropropylene in 80:20 ratio. The reaction of a mixture of vinylidene fluoride/hexafluoropropylene (4555 molar ratio) was carried out after charging into a reactor containing water (1.5 l) and ammonium perfluorooctanoate (7.5 g), at a pressure of 14 kg/cm2G, with addition of I(CF2)4I (0.5 ml), at 80degreesC, and aqueous 10% APS (10 ml). More gas mixture was introduced later and further polymerization to give a dispersion (24 wt.% solid concentration). Then the dispersion (500 ml) was diluted with water (500 ml) and vinylidene fluoride was added for copolymerization at 22 kg/cm2G, 80degreesC, for 50 min to afford the product (15 wt.% solid concentration; epsilon = 1.26 dl/g at 35degreesC; segment (a) content = 9.7 wt.%; and soluble in hot acetone). A polymer gel electrolyte was prepared from a 100 microm hot-pressed sheet of the above block copolymer by soaking with an electrolyte solution of 1 M LiPF4 in propylene carbonate (20 mg) in argon at 60degreesC overnight. Properties of the resulting gel electrolyte: ionic conductivity = 3 x 10-4 S/cm, tested at 20 Hz to 1 kHz by the conventional alternating current impedance method.