NOVELTY - A nonaqueous electrolytic solution (S1) comprises: a solvent, an electrolyte salt, a polyacid and/or a polyacid compound, and a monofluorophosphate and/or a difluorophosphate.    USE - As nonaqueous electrolytic solution, useful for a battery (preferably nonaqueous electrolyte battery) (claimed). The battery is lithium ion secondary battery, and is useful in portable electronic appliances such as video camera, mobile phone and laptop personal computer.    ADVANTAGE - In the nonaqueous electrolytic solution for nonaqueous electrolyte battery the added of polyacid and/or polyacid compound is able to intercalate and deintercalate lithium ion; and forms coating that acts as stable SEI (solid electrolyte interface coating) on negative electrode by charge/discharge at initial stage of use, and suppresses decomposition of solvent and electrolyte salt in nonaqueous electrolytic solution. Thus the SEI containing polyacid and/or polyacid compound is inorganic, firm, and is simultaneously small in resistance on occasion of intercalating and deintercalating lithium ion, and hence deterioration of battery capacity is hardly caused. Further, when monofluorophosphate and/or the difluorophosphate which is closed in component to lithium salt in electrolytic solution is added together with polyacid and/or polyacid compound, decomposition of main electrolyte salt is more suppressed, so that SEI with low resistance can be formed. Thus, not only increase of resistance following a charge/discharge cycle can be suppressed; but further even when battery temperature increases at time of high-temperature use or at time of large-current discharge, side reaction between electrode active material and electrolytic solution is suppressed, so that battery characteristics are improved. The heteropolyacid or heteropolyacid compound takes a kegging structure, is easily soluble in solvent, is stable in battery and is hard to give adverse influences such as reaction with other material.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a battery comprising: a positive electrode (21), a negative electrode (22), and the nonaqueous electrolytic solution (S1).    DESCRIPTION OF DRAWING(S) - The figure shows a sectional view of the nonaqueous electrolyte battery.    Battery lid (14)    Wound electrode body (20)    Positive electrode (21)    Negative electrode (22)    Separator (23)