In order to obtain a non-aqueous electrolyte secondary battery having a high capacity and excellent charge/discharge cycle characteristics, a halogen-containing organic magnesium compound represented by the formula (1): RMgX, where R is an aliphatic hydrocarbon group or an aromatic hydrocarbon group, X is fluorine atom, chlorine atom, bromine atom or iodine atom; or the formula (2): RMgY, where R is an aliphatic hydrocarbon group or an aromatic hydrocarbon group, Y is —ClO4−, —BF4−, —PF6− or —CF3SO3− is added to the non-aqueous electrolyte.