NOVELTY - The battery has a separator (1) which is arranged between the positive and negative electrodes (2,3) respectively contained with the positive and negative electrode active materials, and a fused salt electrolyte. The fused salt electrolyte is provided to contain 70% or more mass of ionic liquids. The ionic liquid is provided to contain an anion and a cation containing a sodium ion. The positive electrode active material is made to contain a polyanion-type sodium manganese silicate compound. The element is selected from iron, cobalt, chromium, titanium, and nickel.    USE - Sodium molten salt battery for domestic-use and industrial large sized electric power storage apparatus, electric vehicle, and hybrid vehicle.    ADVANTAGE - The ionic liquid is provided to contain anion and cation containing sodium ion and the positive electrode active material is made to contain a polyanion-type sodium manganese silicate compound so that the elution of manganese from positive electrode active material is suppressed by combining the fused salt electrolyte even when the battery temperature is high and the deterioration of positive electrode active material is suppressed so as to improve the cycle life and cycling characteristics of sodium molten salt battery. Thus, the generation of internal short circuit by precipitation of eluted manganese is suppressed while suppressing the fall of cycle life from a point. Hence, the thermal-stability of fused salt electrolyte is improved easily for ensuring the safety to fit continuous use by high-temperature range while reducing the manufacturing cost of sodium molten salt battery and the melting point and/or the viscosity of fused salt electrolyte to improve sodium ion conductivity and ensure high capacitance.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method for using sodium molten salt battery.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of the sodium molten salt battery.    Separator (1)    Positive electrode (2)    Negative electrode (3)    External positive electrode terminal (14)    Safety valve (16)