Study On Coating Modification Of Nickel-Rich Ternary LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Materials

LiNi_0.8Co_0.1Mn_0.1O₂（LNCM811）,a nickel-rich ternary cathode material,is considered as one of the candidate cathode materials in the next generation of high-energy lithium ion batteries due to its high energy density.However,LNCM811has some issues,such as low cycle performance,low-rate performance and poor thermal stability,which restrict its commercialization process.At present,coating modification is widely used to improve the above related properties.However,most of the coating materials have the problems of poor adhesion and low electrical conductivity,which is extremely limited in improving the performance of LNCM811.In this paper,the coating was used as the modification means of nickel-rich ternary cathode material LiNi_0.8Co_0.1Mn_0.1O₂.To improve the electrochemical performance of cathode material,coating materials with excellent performance were studied.The main research contents and conclusions of this paper include:（1）Se-coated LiNi_0.8Co_0.1Mn_0.1O₂ ternary cathode material.Se was uniformly coated on the surface of LNCM811 via a facile melt-diffusion approach.The uniform and dense Se coating should attribute to the strong interactions of the exposed Ni,Co,and Mn atoms with Se coating through the formation of metal-Se bonds.Se coating effectively reduces the contacts at the electrode-electrolyte interface and improves the electrical conductivity of the LiNi_0.8Co_0.1Mn_0.1O₂ thus improving the electrochemical performance of LNCM811.Se-coated LiNi_0.8Co_0.1Mn_0.1O₂ exhibited a capacity retention of 72.6%at the 400^th cycle at 5 C.（2）LiTi₂（PO₄）₃-coated LiNi_0.8Co_0.1Mn_0.1O₂ ternary cathode material.Fast ionic conductor LiTi₂（PO₄）₃（LTP）was uniformly coated on the surface of LNCM811 via an in situ reaction of the residual Li⁺on the LNCM811 surface with the added Li-reactive coating materials C₈H₂₀O₄Ti and（NH₄）H₂PO₄.This in situ reactive coating method is favorable to remove the undesired Li⁺which are residual on the LNCM811 surface.Moreover,the obtained uniform LTP coating layers could not only inhibit the side reaction at the electrode-electrolyte interface,but also ensure the fast Li⁺conductivity for the LNCM811 cathode materials during the charge and discharge cycling,thus improving the electrochemical performance of LNCM811.LiTi₂（PO₄）₃-coated LiNi_0.8Co_0.1Mn_0.1O₂ exhibited a discharge capacity of 162 m Ah g^-1 at the 150^th cycle at 0.2 C and 130 m Ah g^-1 at the 180^th cycle at 2 C.（3）Polydopamine assisted LiAl O₂-coated LiNi_0.8Co_0.1Mn_0.1O₂ ternary cathode material.Polydopamine assisted LiAl O₂（PLAO）was uniformly coated on the surface of LNCM811 via a simple precipitation method.The strong adhesion of the LNCM811 surfaces should thanks to the assistance of Polydopamine（PDA）,resulting in the conformal and homogenous deposition of Lithium-ion conductive coating material LiAl O₂ layer.The PLAO coating layers could not only prohibit the side reaction at the electrode-electrolyte interface,but also facilitate lithium ion diffusion,thus improving the electrochemical performance of LNCM811.Polydopamine assisted LiAl O₂-coated LiNi_0.8Co_0.1Mn_0.1O₂ exhibited a discharge capacity of 114m Ah g^-1 at the 200^th cycle at 5 C.