Modification And Electrochemical Properties Of Li-rich Cathode Material

The lithium-manganese-based layered cathode material is a hotspot material in recent years.It has a high energy density,a large specific capacity,and a low cost,but it also has shortcomings.Its first charge-discharge efficiency is not high,its rate and cycle performance are poor,its charge voltage is high,and its compatibility with the currently used electrolyte is low,making it still at the research stage.It is still difficult to realize large-scale commercialization.Surface coating and doping is the main method to modify it.By coating it on the surface,the material can be prevented from directly reacting with the electrolyte and make the material more suitable for the electrolyte.By incorporating other metal elements into the material,the crystal structure can be improved,the stability of the material can be enhanced,and the rate performance and first time efficiency can be effectively improved.In this study,the electrochemical performance was improved by coating,surface pretreatment,and transition metal doping.The material was wet-coated with Li₃VO₄ to obtain several sets of samples with different coating amounts.Through the characterization and electrochemical performance tests,the results show that the electrochemical properties of the coating on the sample improve significantly,including the initial discharge capacity,coulombic efficiency,cycle performance and rate capability.The 3%wt coated sample had the best overall performance,with the initial discharge specific capacity of 243.2mAh/g and the Coulomb efficiency of 70.9%.After 50 cycles at1C,the highest capacity retention rate was 87.2%.However,the coating has a direct effect on the lithium ion transmission distance and the transmission rate,and too much coating causes the charge transfer resistance to increase.The surface of the material was pretreated with reducing sugars to obtain several sets of samples with different modification times.Through the characterization and electrochemical performance tests,the results show that the electrochemical performance of the reducing sugar on the sample is improved significantly,including the initial discharge capacity,coulombic efficiency,cycle performance and rate capability.The five-hour modified sample had the best overall performance,with the highest lithium ion diffusion coefficient,the first discharge specific capacity of 262.4 mAh/g,and the Coulomb efficiency of 80.7%;after 50 cycles at 1C,the capacity retention rate was as high as 97.2%.Using the same batch of four lithium-rich precursors provided by Jinchi Energy Materials Co.,Ltd.,the lithium-rich cathode materials required for the experiment were sintered at different temperatures set.Through the characterization and electrochemical performance tests,the results show that the vanadiumdopingimprovestheelectrochemicalperformanceof Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ samples,including initial discharge capacity,Coulomb efficiency,and cycle performance.At 910°C,the electrochemical performance of the sample was optimal,the first discharge specific capacity was 78.6mAh/g,the Coulomb efficiency was 70.3%,and after 50 cycles at 1C,the capacity retention rate was 71.8%.The Li_1.2(Ni_0.2Mn_0.6)O₂ sample has the best electrochemical performance at the sintering temperature of 920°C.The initial discharge specific capacity is153.6mAh/g,the Coulomb efficiency is 72.8%,but the vanadium-doped precursor is Sintering at the same temperature,the resulting cathode material has an impurity peak,indicating that a small amount of V doping affects the crystal structure of the material,destroys the material structure,and greatly reduces the electrochemical performance of the material.