TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: In the solid polymer electrolyte composition, the average number of repetiting units of ethylene oxide included in R1 to R8 in Formula (1) is in the range of 4-44. The content of the polyhedral silsesquioxane is in the range of 5-50 wt.% with respect to a total weight of the solid polymer electrolyte composition. The polymer matrix includes a member selected from poly(ethylene oxide), poly(propylene oxide), poly(acrylonitrile), poly(vinyl chloride), poly(vinylidene fluoride), poly(methyl methacrylate), polysiloxane, polyphosphazene, and combinations. The polymer matrix has a molecular weight of 1000000 or more. The organic solvent is selected from carbonates, esters, ethers, ketones, nitriles, and combinations. The solid polymer electrolyte composition further comprises a lithium salt, where the lithium salt includes a member selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium chloride, lithium triflate, lithium hexafluoroarsenate, lithium sulfide , lithium sulfate, lithium phosphate, lithium citrate, lithium bis(oxalato)borate, lithium bis(nonafluorosulfonyl)methane, lithium difluoro bisoxalato phosphate, lithium difluoro(oxalato)borate, lithium bis(pentafluoroethylsulfonyl)amide, lithium bis(trifluoromethanesulfonyl)imide, lithium tris(trifluoromethanesulfonyl)methide, and combinations. The molar ratio between the ethylene oxide included in the solid polymer electrolyte composition and lithium included in the lithium salt is in the range of 4:1-60:1. Preferred Battery: In the lithium secondary battery, the cathode includes a member selected from LiMn2O4, LiNi2O4, LiTi2O4, LiTiS2, LiCoO2, LiNiO2, LiMnO2, Li2MnO3, LiFePO4, LiFePO4, LiFePO4F, LiMnPO4, LiCoPO4, LiNiPO4, and combinations. The anode includes a member selected from graphite, graphene, carbon fired at a low temperature, fired cokes, vanadium oxide, lithium vanadium oxide, lithium germanium oxide, lithium titanate oxide, silicon, silica, lithium silicide, and combinations. EXAMPLE - No suitable example given.