Lithium manganese iron phosphate positive electrode active material and preparation method, positive electrode plate, secondary battery and electrical apparatus thereof

A preparation method for a manganese iron lithium phosphate cathode active material comprises the following steps:

• S1, preparing a nano-sized iron oxide by low-temperature solid-phase reaction:
• mix an iron source, a solid base and a doping element M source (if any) for 20 min to 60 min to cause a low-temperature solid phase reaction among the components;
• after a mixing and grinding, let it stand to ensure the complete low-temperature solid-phase reaction;
• wash and remove impurities from the obtained product and dry it at a temperature below 100° C. to obtain nano-sized iron oxide, where the doping element M represents the doping element at the manganese and iron sites;
• S2, spray drying granulation:
• mix the nano-sized iron oxide in S1 with a solvent, a lithium source, a manganese source, a phosphorus source, a doping element N source (if any), a doping element Q source (if any), and a doping element R source (if any) in a predetermined portion and grind them;
• after the grinding is completed, spray dry and granulate to obtain powder, wherein the doping element N represents the doping element at the lithium site, the doping element Q represents the doping element at the phosphorus site, and the doping element R represents the doping element at the oxygen site;
• S3, sintering, which includes the steps:
• S31, pre-sintering the powder obtained in S2 at 350° C. to 550° C. in an air atmosphere or a protective gas atmosphere, and after the reaction, obtain the pre-sintered material;
• S32, grinding the pre-sintered material obtained in S31 and spray dry granulate to obtain pre-sintered material powder;
• S33, sintering the pre-sintered material powder obtained in S32 at 650° C. to 750° C. in a protective gas atmosphere to obtain the phosphorus manganese iron lithium phosphate cathode active material,
• where the molar ratio of the iron source to the solid base is 1:(1-3),
• the washing and impurity removal process includes water washing and alcohol washing,
• the solvent includes ethanol, water or their mixed solvents.