Study On Composition Optimization And Electrochemical Performance Of 523-type Ternary Ni-Co-Mn Cathode Material

The cathode material is an important part of lithium-ion batteries,which is the bottleneck that limits the performance improvement of lithium-ion batteries.Among the new generation ternary LiNi_xCo_yMn_zO₂?x+y+z=1?series of cathode materials,the 523 type ternary Ni-Co-Mn cathode material represented by LiNi_0.5Co_0.2Mn_0.3O₂material has the advantages of high specific capacity with good safety and low cost,which is one of the most promising cathode materials for commercially applications.However,due to defects such as severe cation mixing,poor interface stability,and unstable layer structure,the cycle performance and rate performance of the material are unsatisfactory,which further affects the energy density and power density of lithium-ion batteries.In order to further improve the performance of the material,the transition metal?TM?ion ratio optimization of the 523 type ternary Ni-Co-Mn cathode material and the simultaneous doping-coating dual modification of the optimized material are studied in this paper,and the influence on the crystal structure,interface chemistry,and lithium ion transport properties of materials is systematically analyze.The main research contents are as follows:?1?The SNEI method is developed to optimize the TM ion ratio of LiNi_0.5+xCo_0.2+yMn_0.3+zO₂?x+y+z=0,and the absolute values of x,y and z are not more than 0.03?,which combines the simplex method with the normalization method of evaluation index.This method can significantly improve the optimization efficiency.After only three times of simplex operation,the optimum component of LiNi_0.493Co_0.214Mn_0.293O₂ is obtained.The results show that the electrochemical properties of material have improved significantly through slightly adjustment of the ratio of TM ion,and LiNi_0.493Co_0.214Mn_0.293O₂-based cells exhibit long cycle life and good rate capability due to the low degree of Li⁺/Ni²⁺mixing,a small amount of active lithium ion loss and the slow increase of impedance during cycling.Simultaneously,the impact of the intensity of the TM ion ratio on electrochemical performances is studied.the following trend is observed in decreasing the sensitivity of the evaluation indexes:cycle performance>rate capacity>specific capacity.?2?In order to further improve the cyclic stability of LiNi_0.493Co_0.214Mn_0.293O₂material.Assembling LiNi_0.493Co_0.214Mn_0.293O₂/Li half-cell material with aluminum bis?oxalato?borate-?Al?BOB?₃?-based electrolyte,and perform pre-cycle to achieve the simultaneously double modification of Al³⁺doping and surface passivation film coating of LiNi_0.493Co_0.214Mn_0.293O₂.After double modification,the cycling performance of LiNi_0.493Co_0.214Mn_0.293O₂ is significantly improved.The capacity retention of the dual modified materials is 97.7%after 100 cycles,but that of the pristine is only 85.9%.Al³⁺doping can maintain layered structure stability and suppress the cation-mixing degree,which facilitates lithium ion transport.BOB^-can decompose on the surface of the material to form a passivation film,which can not only block directly contact between the material and the electrolyte,but also inhibit electrolyte decomposition and interface side reactions.Therefore,the synergy of double modification can inhibit structural degradation and improve stability of electrode-electrolyte interface,which effectively improve the electrochemical performance of materials.In summary,SENI method is used to optimiz the ratio of TM ion and Al?BOB?₃-based electrolyte is pre-cycle to achieve the simultaneously double modification of LiNi_0.493Co_0.214Mn_0.293O₂.The electrochemical performance of the material can be significantly improved.These modification strategies are novel and effective,which provide new ideas for the study of cathode materials.