Preparation And Modification Of Ternary Cathode Material LiNi_0.6Cn_0.2Mn_0.2O₂ For Lithium-ion Battery

Lithium-ion batteries are widely used in various types of electric energy storage devices due to many advantages such as high operating voltage,good cycle stability and environmental friendliness.The positive electrode material has become the focus on research and development of battery for its important influence on working voltage,energy density and power density.Compared with other cathode materials,LiNi_0.6Co_0.2Mn_0.2O₂ has the advantages of low cost and high specific capacity,and is a new cathode material with industrial application prospects.However,there are still some defects such as serious Li⁺/Ni²⁺cationic mixing,easily the side reactions between surface residual alkali and electrolyte,and prone to dissolve transition metal in the practical application.In order to further improve the electrochemical performance of LiNi_0.6Co_0.2Mn_0.2O₂ cathode material,the defects above are mainly modified mainly modified by coating and doping,etc in this paper.The research work mainly includes following two aspects:?1?The LiNi_0.6Co_0.2Mn_0.2O₂ cathode material is synthesized by way of carbonate coprecipitation and modified by high temperature diffusion coating with Al₂O₃.The thin and uniform coating formed by high-temperature Al₂O₃ diffusion coating not only effectively reduces the degree of Li⁺/Ni²⁺cation mixing in the material,but also inhibits the formation of residual alkali on the surface of the positive electrode material and the side reactions between the positive electrode particles and the electrolyte,and accelerates the transport rate of Li⁺during charge anddischarge,therebyimprovingtheelectrochemicalpropertiesof LiNi_0.6Co_0.2Mn_0.2O₂ material.?2?Although the performance of materials was effectively improved by wet coating,there are still problems such as serious energy consumption and high cost in industrial application.Therefore,in addition to the coating modification,the structure of LiNi_0.6Co_0.2Mn_0.2O₂ is specially designed and supplemented with doping means to further improve the material properties.Firstly,the core-shell structure of LiNi_0.6Co_0.2Mn_0.2O₂ material with a core composition of LiNi_0.8Co_0.1Mn_0.1O₂ and a shell composition of LiNi_0.2Co_0.4Mn_0.4O₂ was synthesized by the method of carbonate coprecipitation.Although the defects of LiNi_0.6Co_0.2Mn_0.2O₂ material are improved by the core-shell structure material to a certain extent,it still has problems such as Li⁺/Ni²⁺cationic mixing,easily structural phase change,surface residual alkali hindering Li⁺transmission,easy to have side reactions with electrolyte and core shell separation.Therefore,the core-shell LiNi_0.6Co_0.2Mn_0.2O₂ material is modified by Mg doping,and the LiNi_0.6Co_0.2Mn_0.2O₂ materials with core-doped Mg,shell-doped Mg,and core-shell co-doped Mg are prepared,respectively in this paper.By comparing different ways of Mg doping materials,it is found that the LiNi_0.6Co_0.2Mn_0.2O₂material with shell-doped Mg has better electrochemical performance.This is mainly because the doping of Mg in the shell layer can enhance the bond energy of the metal bond of the surface layer,maintain the stability of the surface structure of the material effectively,and inhibit the irreversible transition of the surface of the material,thereby reducing the dissolution of the transition metal.At the same time,the interlayer distance of Li⁺transmission increase by doping Mg in the shell of the material,which reduces the degree of Li⁺/Ni²⁺mixing in the material effectively,then promotes the charge transfer reaction in the layered structure material,and finally improves electrochemical performance of LiNi_0.6Co_0.2Mn_0.2O₂ material.In summary,LiNi_0.6Co_0.2Mn_0.2O₂ has a great potential as a high energy density cathode material.In order to overcome the shortcomings of LiNi_0.6Co_0.2Mn_0.2O₂material,the diffusion coating of Al₂O₃ and the modification of core-shell structure doped with Mg have been carried out,which reduces the mixing degree of Li⁺/Ni²⁺in the material and inhibits the side reaction between the residual alkali and the electrolyte on the surface of the material.At the same time,the dissolution of the transition metal in the material is inhibited.As a result,the electrochemical performance of the LiNi_0.6Co_0.2Mn_0.2O₂ material is effectively improved,which provides guidance for industrial application.