TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Solvent: The solvent is aprotic organic solvent.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Electrolyte: The solid electrolyte has decomposition voltage of 3V or more.Preferred Process: Especially, a hydrated lithium sulfide as one component (I) and the component (II) comprising lithium component, sulfur component, and phosphorus, silicon, boron and/or germanium are added, and reacted. A lithium compound (A) having basicity as component (III) is added to the reaction content, and reacted. A compound (B), and a polymer component are further added to the reaction content.Preferred Lithium Compound: The lithium compound (A) having basicity is one, or two or more of compounds chosen from n-butyl lithium, sec-butyl lithium, tert-butyl lithium, hexyl lithium and lithium alkoxide. The compound (B) is one, or two or more of compounds chosen from lithium phosphate, lithium borate, lithium silicate and lithium sulfate. SPECIFIC COMPOUNDS - The organic solvent is N-methyl-2-pyrrolidone. The lithium component is lithium sulfide. The components of phosphorus, silicon, boron and germanium are phosphorus sulfide, silicon sulfide, boron sulfide and germanium sulfide.    EXAMPLE - N-methyl-2-pyrrolidone (NMP) (in g) (3326.4) and lithium hydroxide (287.4) were taken in an autoclave, and stir-reacted at 130degreesC to form reaction liquid having sulfur to lithium molar ratio of 0.996. High purity hydrated lithium sulfide was added for 2 hours. The temperature of the reaction solution was raised under nitrogen stream. A portion hydrogen sulfide reacted was removed. Water produced as by-product by the reaction of hydrogen sulfide and lithium hydroxide was evaporated and extracted out of the reaction system. The temperature of the reaction solution was raised to 180degreesC. The removal of hydrogen sulfide was completed within 50-80 minutes. High purity lithium sulfide was precipitated in the solvent. The content was cooled, and filtered. The obtained residue was washed twice-using acetone, and dried to obtain white powder of lithium sulfide having purity of 99.8 % with yield of 92 %. Obtained lithium sulfide (4.526), phosphorus sulfide (5.474) and NMP (200 ml) were taken in a flask, and stir-mixed under nitrogen atmosphere. The reaction material was heated to 150 degreesC, and reacted at 150 degreesC for 3 hours to obtain green homogeneous solution. The reaction material was extracted using a syringe, and filled in a bottle having nitrogen. Toluene (150 ml) was poured into the solution, and solid substance was precipitated. The solid content was washed repeatedly using toluene, and vacuum dried at 150 degreesC for 5 hours to obtain solid of ash colored powder (3.05). The solid had ionic conductivity of 8x10-5 S/cm. The solid was heat processed at 230 degreesC. The obtained solid had ionic conductivity of 4x10-4 S/cm. The obtained solid used as lithium ion electroconductive solid electrolyte.