TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Component: The secondary battery contains spinel-type lithium-containing complex oxide. The positive electrode occludes lithium and discharges as positive electrode active material. The negative electrode contains a material which is capable of occluding and discharging lithium, and lithium alloy.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The supporting electrolyte is lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluoroantimonate, lithium perchlorate, lithium hexachloroaluminate, and/or lithium-containing compound (LiN(CpF2p+1SO2)(CqF2q+1SO2), where p and q are positive integers). The material which is capable of occluding and discharging the lithium, is carbon material or oxide. The carbon material is graphite or amorphous carbon.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The aprotic solvent is cyclic carbonate, linear carbonate, aliphatic carboxylate, ( gamma )-lactone, cyclic ether, chain-shaped ether, and/or their fluorine derivatives. The additive contains phosphazene compound of formula: -(P(-X1)(-X2)=N)n- (IV), disulfonic-acid ester of formula (V), disulfonic-acid ester of formula: R14-S(=O)2-C(-R15)(-R12)-S(=O)2-R13 (VI), sultone compound of formula (VII), and vinylene carbonate or its derivative.X1,X2=halo, alkyl, alkoxy, aryl, acyl, aryloxy, amino, alkylthio, arylthio, haloalkyl, haloalkoxy, haloaryl, haloacyl, haloaryloxy, haloamino, haloalkylthio or haloarylthio;n=3-5;X1+R2=ring;Q=O, methylene or single bond;A1=(un)substituted 1-5C optionally branched alkylene, carbonyl, sulfinyl, (un)substituted optionally branched 1-5C perfluoroalkylene, 2-6C (un)substituted optionally branched fluoroalkylene, 1-6C (un)substituted optionally branched alkylene having ether bond, 2-6C (un)substituted optionally branched fluoroalkylene containing ether bond or 1-6C (un)substituted optionally branched perfluoroalkylene having ether bond;A2=(un)substituted optionally branched alkylene;R12,R15=1-5C alkyl, 1-5C alkoxy, 1-5C fluoroalkyl, 1-5C polyfluoroalkyl (all optionally substituted), H, -SO2X3, XY1, -COZ or halo;X3,Y1=(un)substituted 1-5C alkyl;Z,X4,X5,Y2-Y4=H or (un)substituted 1-5C alkyl;R13,R14=1-5C alkyl, 1-5C alkoxy, fluoroalkyl, 1-5C phenoxy, 1-5C fluoroalkoxy (all optionally substituted), 1-5C polyfluoroalkyl, 1-5C polyfluoroalkoxy, hydroxyl, halo, -NX4X5 or -NY2CONY3Y4;R16-R21=H, 1-12C alkyl, 3-6C cycloalkyl or 6-12C aryl;andm=0, 1 or 2.    TECHNOLOGY FOCUS - POLYMERS - Preferred Component: The polymer is (meth)acrylate polymer having phosphazene structure in one or more side chains or crosslinked component obtained by crosslinking a copolymer obtained by copolymerizing ether-type monomer of formula: H2C=C(-R1)-R2-OCH2-R2 (I), ethane-type monomer of formula: H2C=C(-R4)-R5 (II), and phosphazene structure-containing monomer of formula: H2C=C(-R6)-R7-R8-R9 (III). The content of nitrogen in the polymeric phosphazene structure is 0.0007-7 %mass with respect to total content of polymer electrolyte. The polymer electrolyte further contains an aprotic solvent and additive.R1,R4,R6=H or methyl;R2,R7=carbonyl or methyl;R3=group of formula (i)-(iv);R5=-COOCH3, -COOC2H5, -COOCH2CH2CH3, -COOCH(CH3)2, -COO(CH2CH2O)nCH3, -COO(CH2CH2O)nC2H5, -COO(CH2CH2O)nC3H7, -COO(CH2CH2O)nC4H9, -COO(CH2CH(CH3)O)nCH3, -COO(CH2CH(CH3)O)nC2H5, -OCOCH3, -OCOC2H5 or -CH2OC2H5;n=1-3;R8=O or -O-R11-O-;R11=(un)substituted optionally branched 1-5C alkylene;R9=(un)substituted cyclotriphosphazene or polyphosphazene;andR10=1-6C alkyl.