NONAQUEOUS ELECTROLYTE SECONDARY BATTERY

This invention provides a method for producing a non-aqueous electrolyte secondary battery. The method comprises constructing a battery cell that comprises a positive electrode comprising a positive electrode active material, a negative electrode comprising a negative electrode active material, and a non-aqueous electrolyte solution comprising a non-aqueous solvent and an oxalatoborate-based compound. The method further comprises charging the battery cell to form on the negative electrode a layer that is derived from the oxalatoborate-based compound and comprises boron and oxalate ions. The method further comprises carrying out a modification treatment to increase the ratio of number of moles m B of boron to number of moles m A of oxalate ions in the layer.