NOVELTY - A non-aqueous electrolyte composition contains metal ion (A) in high concentration and metal ion (B) (0.01-0.2 mol/kg). The ionic radius of metal ion (B) is greater than the ionic radius of metal ion (A).    USE - Non-aqueous electrolyte composition is used for non-aqueous electrolyte secondary battery such as lithium ion secondary battery (claimed) used as power supply for portable electronic devices such as camcorder, digital still camera, mobile information terminal, notebook-type computer and mobile telephone.    ADVANTAGE - The precipitation of metal ion (A) in the non-aqueous electrolyte composition is prevented, and the disassembly of organic solvent in electrolyte solution is suppressed. The non-aqueous electrolyte secondary battery comprising the composition has improved initial charging and discharging efficiency, and favorable charging and discharging cycle characteristic. Swelling of battery during storage at high temperature is prevented.    DETAILED DESCRIPTION - A non-aqueous electrolyte composition contains metal ion (A) in high concentration and metal ion (B) (0.01-0.2 mol/kg). The ionic radius of metal ion (B) is greater than the ionic radius of metal ion (A). The metal ion (A) is lithium ion. The metal ion (B) is sodium ion, potassium ion, rubidium ion and/or cesium ion, preferably sodium ion or potassium ion. The metal ion (B) is formed by adding alkali metal salt of hexafluorophosphoric acid, arsenate hexafluoride, tetrafluoroboric acid, perchlorate, trifluoromethane sulfonic acid or bis(trifluoromethane sulfonyl)imide to the non-aqueous electrolyte composition. The composition further contains halogenated carbonate and carbonate having carbon-carbon multiple bonds. The non-aqueous electrolyte secondary battery has a high molecular compound such as polyvinylidene fluoride swollen by the non-aqueous electrolyte.    DESCRIPTION OF DRAWING(S) - The drawing shows an exploded perspective view of structure of non-aqueous electrolyte secondary battery. (Drawing includes non-English language text)    Winding electrode (20)    Positive electrode lead (21)    Negative electrode lead (22)    Exterior Component (30)    Contact film (31)