TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The lithium salt is lithium compound of formula: LiN(SO2CkF2k+1)2, LiPFn(Ck1F2k1+1)6-n or LiNSO2CkF2k+1, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium arsenic hexafluoride and/or lithium-silicon fluoride. The electrolyte solution further contains difluoro lithium phosphate and/or monofluoro lithium phosphate. The positive electrode active material has discharge capacity of 10 mAh/g or more in electric potential of 4.1 V (vs lithium/monovalent lithium ion) or more. The positive electrode active material contains oxide of formula: LiMn2-xMaxO4 and/or LiMn1-uMeuO2, complex oxide of formula: zLi2McO3-(1-z)LiMdO2 and/or lithium compound of formula: LiMb1-yFeyPO4 and/or Li2MfPO4F.k=0-8;n=1-5;k1=1-8;Ma,Mc,Md,Mf=transition metal;x=0.2-0.7;Me=transition metal excluding Mn;u,z=0.1-0.9;Mb=Mn or Co;andy=0-0.9.Preferred Property: The positive electrode has electric potential of 4.1 V (vs lithium/monovalent lithium ion) or more based on lithium standard during full charging.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The content of basic compound and/or silicon compound is 10 mass ppm to 50 %mass with respect to 100 %mass silyl group-containing compound. The silyl group-containing compound (A) is of formulae (A2)-(A4).Eg: Ra9-C(=O)-O-Si(Ra1)(Ra2)(Ra3) (A4) The Lewis base is nitrogen-containing organic Lewis base. The content of silyl group-containing compound is 0.01-10 %mass with respect to 100 %mass electrolyte solution. The nonaqueous solvent is cyclic carbonate and/or linear carbonate. The basic compound is compound containing silicon-nitrogen bonding.M1,M2=P or B;Ra6=1-20C hydrocarbyl, 1-20C alkoxy (both optionally substituted), OH, OLi, 1-20C siloxy or OP(O)l(Ra7Ra8);Ra4,Ra5,Ra7,Ra8=1-20C hydrocarbyl, 1-20C alkoxy (both optionally substituted), OH, OLi or 1-20C siloxy;m=1-20;l,n=0 or 1;j=2-20;andRa9=1-20C hydrocarbyl.(i) When M1 is P, n is 0 or 1; (ii) When M1 is B, n is 0; (iii) When M2 is P, k is 0 or 1; and (iv) When M2 is B, k is 0.