NOVELTY - A nonaqueous electrolyte secondary battery (10) comprises flat winding electrode assembly formed by winding an elongated positive electrode and an elongated negative electrode with an elongated separator interposed between elongated positive electrode and an elongated negative electrode, and an outer component (25) for storing the flat winding electrode assembly and a nonaqueous electrolyte. The nonaqueous electrolyte comprises lithium salt comprising oxalate complex as an anion and/or lithium difluorophosphate during formation of nonaqueous electrolyte secondary battery.    USE - Nonaqueous electrolyte secondary battery e.g. lithium-ion battery is used as power supply of portable electronic equipment e.g. smartphone, portable personal computer, personal digital assistant and portable music player, electric vehicle, and hybrid electric vehicle e.g. plug-in hybrid electric vehicle.    ADVANTAGE - The safe and reliable nonaqueous electrolyte secondary battery has high capacity and output characteristics, and excellent cycle characteristics, and charge storage characteristics by preventing decomposition of nonaqueous electrolyte due to the contact between active material and nonaqueous electrolyte. The nonaqueous electrolyte secondary battery allows nonaqueous electrolyte having high viscosity to easily penetrate inside of flat winding electrode assembly.    DETAILED DESCRIPTION - A nonaqueous electrolyte secondary battery comprises flat winding electrode assembly formed by winding an elongated positive electrode and an elongated negative electrode with an elongated separator interposed between elongated positive electrode and an elongated negative electrode, and an outer component for storing the flat winding electrode assembly and a nonaqueous electrolyte. The nonaqueous electrolyte comprises lithium salt comprising oxalate complex as an anion and/or lithium difluorophosphate during formation of nonaqueous electrolyte secondary battery. The flat winding electrode assembly has 8 or more layers of winding portion formed only of the separator in the central portion flat winding electrode assembly.    DESCRIPTION OF DRAWING(S) - The drawing shows a plan view of nonaqueous electrolyte secondary battery.    Nonaqueous electrolyte secondary battery (10)    Positive electrode terminal (18)    Negative electrode terminal (20)    Sealing plate (23)    Outer component (25)