TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Salt: The lithium salt is lithium hexafluoro phosphate (LiPF6), lithium tetrafluoro borate (LiBF4), LiAsF6, LiSbF6, LiClO4, LiAlCl4, LiN(CkF2k+1SO2)2 (where k is 1 or 2), or LiN(CmF2m+1SO2)(CnF2n+1SO2) (where m, n are 1 or 2). Preferred Composition: The anode and the cathode have reversible occlusion and active material layer, which discharges lithium ion. The active material of the anode is lithium-containing complex oxide. The active material of the cathode is metal lithium or lithium alloy, or carbon material which is graphite or amorphous carbon.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The electrolyte liquid contains an aprotic solvent containing at least one type of high dielectric constant aprotic solvent and at least one type of low viscosity aprotic solvent. The aprotic solvent further contains 1,3-propane sultone, 1,4-butane sultone, sulfolane, methyl sulfolane, alkane sulfonic acid anhydride, cyclic disulfonic acid ester compound, gamma-sultone compound or sulfolene compound. At least one type of lithium salt is dissolved in the aprotic solvent as an electrolyte.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Salt: The lithium salt is lithium hexafluoro phosphate (LiPF6), lithium tetrafluoro borate (LiBF4), LiAsF6, LiSbF6, LiClO4, LiAlCl4, LiN(CkF2k+1SO2)2 (where k is 1 or 2), or LiN(CmF2m+1SO2)(CnF2n+1SO2) (where m, n are 1 or 2). Preferred Composition: The anode and the cathode have reversible occlusion and active material layer, which discharges lithium ion. The active material of the anode is lithium-containing complex oxide. The active material of the cathode is metal lithium or lithium alloy, or carbon material which is graphite or amorphous carbon. SPECIFIC COMPOUNDS - Ten 1,3-oxa thiane compounds are disclosed, such as compound of formula (1).    EXAMPLE - Ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 30/70, and aprotic solvent was prepared. Subsequently, lithium hexafluoro phosphate was dissolved in the aprotic solvent by 1 mol/l ratio as an electrolyte. Subsequently, 1,3-oxa thiane compound of formula (1) was added such that the content was 0.5 mass%, and an electrolyte liquid for secondary batteries was obtained. A secondary battery having favorable cycle characteristics, extended life, stability, high energy density and reliability, was produced using the electrolyte liquid.