Synthesis And Modification Of Ni-Rich Ternary Cathode Materials

The emission of internal combustion engine-driven vehicles not only pollutes the environment,but also exacerbates the“greenhouse effect”.Therefore,immense research has been accelerated to the transformation of traditional fuel vehicles into electric vehicles means a true“green”revolution across the world.As a result,many research groups around the world are actively developing power supplies for electric vehicles.Owing to its unique properties such as high open-circuit voltage,high energy and power density,long cycle life,fast charge and discharge and no memory effect have identified the lithium-ion batteries as ultimate choice of power to electronic devices.The positive electrode material greatly influences the cost and performance of the lithium ion battery,and thus has been extensively studied.LiNi_x Co_yMn_1-x-yO₂,a layered cathode material with?-NaFeO₂ structure,has become a key cathode material for research of lithium-ion batteries due to its structural stability,high specific capacity,good cycle performance and high rate performance.Ni-rich LiNi_0.6Co_0.2Mn_0.2O₂ cathode materials have attracted the attention of many researchers due to its unique properties such as higher specific capacity,low cost,etc.However,the issues such as poor rate capability and low energy density hamper this system for applications in hybrid electric vehicles.In order to circumvent these challenges optimization and doping of LiNi_0.6Co_0.2Mn_0.2O₂ cathode materials in the present study of single crystal structural analysis was carried out.The following conclusions have been drawn from the present study.?1?The spherical LiNi_0.6Co_0.2Mn_0.2O₂ cathode materials are agglomerated by nano-sized primary particles,which reduce the specific surface area,can reduce the side reaction with the electrolyte,and have a higher compaction density and improves the electrochemical performance of the material.LiNi_0.6Co_0.2Mn_0.2O₂ cathode material was prepared by high temperature solid-state method,and the influence of lithium salt,sintering temperature and time on material properties were investigated systematically.The results of XRD,SEM,constant current charge-discharge and cyclic voltammetry showed that LiNi_0.6Co_0.2.2 Mn_0.2O₂ cathode prepared by sintering at 480°C for 5 h then sintering at 800°C for 15 h and using Li₂CO₃ as the lithium source has the best electrochemical performance.The initial discharge specific capacities at 0.1 and 1 C rates were 165and 125 mAh g^-1,respectively.After 200 cycles at 1 C rate,the capacity retention rate reached 76%.?2?The performance of LiNi_0.6Co_0.2Mn_0.2O₂ was optimized by element doping modification?F and Cl?.The doped anion enters the inside of the crystal,which not only does not damage the layered structure of the material,but also reduces the cation mixing,stabilizes the structure,improves the specific capacity of the material,and greatly improves the cycle performance and rate performance.When the molar ratio of F^-and Cl^-doping is 0.02,the material has better performance in the rate performance and cycle performance test.The specific capacity of these materials at 0.1 C rate is 173and 179 mAh g^-1,respectively.At 1 C rate,the specific capacity of the materials was135 and 144 mAh g^-1,respectively.After 200 cycles of charge and discharge cycles at1 C-rate,the capacity retention was 83 and 84%,respectively.?3?By using high temperature solid phase method by adding urea as a template,urea will decompose at high temperature to form reticular melam,and ions will be arranged on the network template to form a two-dimensional block structure composed of primary particles.The morphology is novel and unique,with high structural stability,shortening lithium ion transmission distance and improving electron mobility,therefore high battery stability,good cycle stability and small specific surface area,can reduce the contact area with the electrolyte,reduce the occurrence of side reactions between the positive electrode material and the electrolyte,thereby improving the bulk structure of nickel-cobalt-manganese ternary.The specific capacity,rate and cycle performance of the positive electrode material increased the energy density significantally.The first-discharge specific capacity of the bulk LiNi_0.6Co_0.2Mn_0.2O₂cathode material was 162 mAh g^-1 and 121 mAh g^-1 at 0.1 C and 1 C,respectively.After 200 cycles at 1 C rate,the capacity retention rate reached 80%,effectively increasing the specific capacity,rate and cycle performance of the material and increasing the energy density.