TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Component: The conducting salt is lithium salt.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Property: The non-flammable solvent has boiling point of less than 150 degrees C. Preferred Composition: The aprotic polar organic solvent is chosen from cyclic carbonates, cyclic esters of carboxylic acids, cyclic or acyclic sulfone, cyclic or acyclic dinitrile, and ionic liquids. The flame retardant is organic phosphorus compound. The organic phosphorus compound is chosen from cyclophosphazene, phosphoramide, alkyl and/or aryl trisubstituted phosphates, alkyl and/or aryl disubstituted phosphites, alkyl and/or aryl di or trisubstituted phosphonates, alkyl and/or aryl trisubstituted phosphines, alkyl and/or aryl di or trisubstituted phosphinate, and fluorinated derivatives. The non-flammable solvent is chosen from fluorinated di-1-10C alkyl ether, fluorinated di-1-4C-alkyl-2-6C alkylene ethers and polyethers, fluorinated cyclic or linear esters, and fluorinated cyclic or linear carbonates. The amount of hydrogen atoms replaced by fluorine in the solvent is more than 65%. The ester compound is glutaric acid di(1-4C alkyl)ester, preferably glutaric acid dimethyl ester. The content of ester compound and flame retardant and/or non-flammable solvent in the electrolyte composition is 10-50 wt.% and 1-10 wt.%, respectively, with respect to total weight of the composition. The low-viscosity aprotic organic solvent is chosen from linear carbonate, di-1-10C alkyl ether, di-1-4C alkyl-2-6C alkylene ethers and polyethers, cyclic ethers, cyclic or acyclic acetales or ketales, orthocarboxylic acid esters, acyclic esters of carboxylic acids, and acyclic nitriles. The additive is solid electrolyte inter-phase-forming additive, overcharge protection additive, wetting agents, hydrogen fluoride, water scavenger, stabilizer for lithium hexafluorophosphate salt, ionic salvation enhancer, corrosion inhibitors, or gelling agents. The weight ratio of aprotic polar solvent with respect to aprotic organic solvent is (10-60):(10-70):(5-70).