Preparation And Modification Of LiNi_0.5Co_0.2Mn_0.3O₂ Cathode Material For Lithium Ion Batteries Abstract

At present,the market share of electric vehicles has increased rapidly in recent years,and the range and charging speed of on-board batteries have become the focus of people’s attention.Therefore,it is urgent to research and develop lithium batteries with high energy density and high stability at high magnification rate.LiNi_xCo_yMn_1-x-yO₂has attracted widespread attention in recent years.LiNi_xCo_yMn_1-x-yO₂,also as a material with layered structure,has a higher actual capacity than LiCo O₂（LCO）.Besides,because of the low content of Co in the crust and its toxicity,compared with NCM,it has a low cost and is environmentally friendly.Therefore,it is considered to be one of the substitutes of cathode material LCO with the longest development time.Nickel-cobalt-manganese oxide layered materials have the characteristics of high capacity and high density,which is one of the most promising materials for lithium-ion battery（LIBS）.However,due to the existence of cation mixing phenomenon and the transformation of the intermediate structure to spinel structure during the cycle process,its capacity and cycle performance at high cut-off voltage are not good.（1）LiNi_0.5Co_0.2Mn_0.3O₂（NCM523）cathode material with primary dispersed particles was prepared by co-precipitation method and high temperature solid phase method.The synthesis conditions were optimized by comparative experiments.The effects of reaction temperature,transition metal salt solution feeding rate and high temperature solid phase calcination temperature on the morphology,structure and electrochemical properties of the co-precipitation materials were systematically studied.When the reaction temperature of preparing ternary material is 50℃,the feeding rate is 1.6 m L/min,and the calcination temperature is 850℃,the material obtained has the best electrochemical performance,good particle crystallinity,uniform size distribution,good dispersion,and high structural stability.（2）The modified NCM523 was modified by Al element doping,and the electrochemical properties,morphology and crystal structure of the modified material were identified.The modified NCM523 with Al doping amount of 2%reached180.5m Ah/g at 0.5C in the voltage range of 3-4.5V.The capacity retention rate was80.56%after 100 cycles.At 1C,the discharge specific capacity reaches 170.3m Ah/g for the first time,and the capacity retention rate is 78.13%after 100 cycles.Al-doped primary dispersed granular NCM material is of great significance for increasing Li⁺layer spacing and improving the stability and order of the structure.（3）The specific capacity,cycling performance and crystal structure of the modified materials were evaluated by Ti doping or Ti and Na co-doping.Ti and Na co-doped NCM523 has the most obvious effect on increasing the discharge specific capacity and improving the cycle performance.Between of 3-4.5V,the specific discharge capacity reaches 183.5m Ah/g and the capacity retention rate is 81.96%at0.5C after 100 cycles;at 1C,the specific discharge capacity reaches 164.2m Ah/g and the capacity retention rate is 80.93%after 100 cycles.The introduction of Ti and Na plays an important role in improving the cation mixing and enhancing the stability of its crystal structure.