Preparation And Performance Of High-Performance Lithium-Rich Manganese-based Cathode Materials For Lithium Ion Batteries

The lithium-rich manganese-based x Li₂MnO₃·（1-x）LiMO₂（M=Ni,Co,Mn）cathode material is widely considered to be a kind of cathode material due to its high reversible capacity,high working voltage,low production cost,and environmental friendliness,but the material has some defects,which limit its application and development.In order to solve the shortcomings of material cycle and poor rate performance,this paper studies the synthesis process and modification methods,and obtains the material with excellent performance.In this paper,the relationship between the crystal structure,physical morphology and reaction conditions of the material was studied,and the optimal synthesis process of the precur sor of lithium-rich manganese-based cathode material Mn_0.56Ni_0.24（OH）₂ was determined.The effects of reaction temperature,reaction time,stirring speed,and p H value on the morphology,particle size and tap density of the precursor were studied.It was concluded that when ammonia water was used as the complexing agent,Na OH is used as the precipitating agent,when the reaction temperature was controlled at 55℃,the p H value was controlled in the range of 12±0.2,the reaction time was 12 h,and the stirring speed was 1500 rpm,precursor of the prepared lithium-rich manganese based cathode material Mn_0.56Ni_0.24（OH）₂had more regular morphology,with an average particle size of 9.642μm and a tap density of 2.05 g·cm-3.By studying the influence of the high-temperature solid-phase synthesis process on the morphology and electrochemical properties of the material,it was found that when the calcination temperature was 950℃,the calcination time was 24 h,and the ratio of Li₂CO₃ was 1:0.92,the initial coulombic efficiency of the materials was 78.65%.At a current density of0.2 C,the initial discharge capacity reached 271.79 m Ah·g-1,after 100cycles,the capacity remained was 182.98 m Ah·g^-1,and the capacity retention rate was 67.32%.The high temperature solid phase method was used to modify the Li_1.104-3xMn_0.56Ni_0.24Al_xO₂ material.Compared with the XRD curve,it was found that Al³⁺doping does not change its layered structure.When x=0.0025,the electrochemical performance of t he material optimal.At room temperature,in the voltage range of 2.0-4.8 V,the initial discharge capacity of the material at 0.2 C was 271.562 m Ah·g-1,and the initial coulombic efficiency was 82.31%.After 100 times of normal temperature cycling,the capacity was maintained at 234.42 m Ah·g-1,and the capacity retention rate was 86.32%.The Li_1.104Mn_0.56Ni_0.24O₂ cathode material was coated with Na₃PO₄.By studying the structure of materials with different coating amounts,it was found that the layered structure will not be changed after Na ₃PO₄coating,and when the coating amount of Na₃PO₄ was 5.0%,the electrochemical performance of the materials was the best.At room temperature,in the voltage range of 2.0-4.8 V,the initial discharge capacity of the material at 0.2 C was 272.95 m Ah·g-1,and the initial coulombic efficiency was 84.32%.After 100 times of normal temperature cycling,the capacity was maintained at 189.98 m Ah·g-1,and the capacity retention rate was 69.60%.