LITHIUM MANGANESE IRON PHOSPHATE POSITIVE ELECTRODE ACTIVE MATERIAL AND PREPARATION METHOD, POSITIVE ELECTRODE PLATE, SECONDARY BATTERY AND ELECTRICAL APPARATUS THEREOF

A lithium manganese iron phosphate positive electrode active material, preparation method, a positive electrode plate, a secondary battery and an electrical apparatus are disclosed. The method comprises: mixing and grinding an iron source, a solid base and optionally a source of doping element M After grinding, impurities are removed to obtain a nanoscale iron-containing oxide; mixing the obtained nanoscale iron-containing oxide with a solvent, a lithium source, a manganese source, a phosphorus source, optionally a source of doping element N, optionally a source of doping element Q and optionally a source of doping element R in a predetermined ratio and then grinding. After grinding, granulating to obtain a powder; and sintering the powder to obtain the lithium manganese iron phosphate positive electrode active material. A lithium manganese iron phosphate positive electrode active material having both good electrochemical performance and high tap density can be obtained.