Preparation And Study Of LiMnPO₄/C As Cathode Material For Lithium-ion Batteries

LiMnPO₄（Lithium manganese phosphate）,with low cost,good stability and 20%higher energy density than lithium iron phosphate,is a promising cathode material for lithium ion batteries.However,low conductivity of LiMnPO₄ affects its electrochemical performance.It hold great significance to study lithium manganese phosphate and improve the electrical conductivity of the materials for the development and application of LiMnPO₄.In this paper,the study of lithium manganese phosphate composites was carried out by surface nanocrystallization,carbon covering and co-doping at the Mn-site.The EG/H₂O solvent thermal method was used to prepare LiMn_1-xM_xPO₄/C,and a series of physical and chemical properties were tested,including XRD,SEM,charge-discharge performance,CV,EIS and other tests,to explore the relatively excellent modification conditions.This paper studies and conclusion in the following areas:（1）The study of surface nanocrystallization and coating carbon.In this stage,se-veral factors affecting the preparation of LiMn_0.6Fe_0.4PO₄/C were explored,including EG:H₂O volume ratio in water-solvent thermal synthesis,types and amounts of coated carbon sources,calcining temperature,calcining time,amount and types of additives in water-solvent thermal synthesis.The performance tests show that the LiMn_0.6Fe_0.4PO₄/C prepared under optimal conditions is nanorods with a diameter of about 50 nm and a length of 80-150 nm.At the same time,the material exhibit superior discharge specific capacity of 145.92 mAh/g at 0.2 C,and a remarkable stable capacity retention of97.34%after 100 cycles at 0.2 C.（2）The study on co-doped metals.Doped metal M（Mg,Ni,Co）was used to prepare the LiMn_0.9Fe_0.1PO₄/C composite with excellent electrochemical properties.XRD results show that the doped metals have been successfully doped with manganese phosphate lithium phase.Electrochemical performance test shows that doped Co can significantly improve the performance of LiMn_0.9Fe_0.1PO₄/C material.Compared with doped Mg and Ni,doped Co has the highest discharge specific capacity of 141.32mAh/g at 0.2 C after 50cycle and the best multiplier performance.