Study On Coating Modification And Electrochemical Properties Of High Nickel Polycrystalline Cathode Material LiNi_0.8Co_0.1Mn_0.1O₂

High-nickel polycrystalline ternary positive electrode material Li Ni_0.8Co_0.1Mn_0.1O₂has the advantages of high specific capacity and low raw material cost,and is considered a highly valuable high-energy density lithium-ion battery positive electrode material.However,the current polycrystalline Li Ni_0.8Co_0.1Mn_0.1O₂positive electrode material still has problems such as large nickel-lithium disorder in the lattice,high residual alkali content on the surface,and severe electrolyte corrosion,which hinders its large-scale industrial application.This paper starts from the interface coating modification of polycrystalline Li Ni_0.8Co_0.1Mn_0.1O₂positive electrode material and uses organic and inorganic aluminum sources as coating precursors to form a Li Al O₂coating layer on the interface of polycrystalline Li Ni_0.8Co_0.1Mn_0.1O₂positive electrode material,and studies the effect of coating solution,aluminum source dosage,and polymer addition on the structure and performance of Li Al O₂@Li Ni_0.8Co_0.1Mn_0.1O₂（LAO@NCM811）positive electrode material to obtain a high-performance polycrystalline Li Ni_0.8Co_0.1Mn_0.1O₂positive electrode material.The specific research work is as follows:（1）Study on the organic isopropanol aluminum-modified Li Ni_0.8Co_0.1Mn_0.1O₂positive electrode material and its electrochemical performance.Using organic isopropanol aluminum as the coating precursor,an aluminum compound layer is coated on the surface of the Ni_0.8Co_0.1Mn_0.1（OH）₂positive electrode precursor microspheres through a liquid-phase method.After the lithiumization reaction with Li OH under high-temperature conditions,O-LAO@NCM811(Organic Al source-derived Li Al O₂@Li Ni_0.8Co_0.1Mn_0.1O₂)microsphere positive electrode material is obtained.The effects of water and ethanol coating solvents,isopropanol aluminum dosage,and PVP addition on the structure and electrochemical performance of O-LAO@NCM811 are studied.The results show that when ethanol is used as the coating solvent,isopropanol aluminum can obtain a more complete LAO coating layer.The addition of PVP can further enhance the binding effect between the coating precursor and the matrix,improve the uniformity of the coating layer,and obtain high-performance O-LAO@NCM811 positive electrode material.When the isopropanol aluminum dosage in the ethanol coating solution is 1.5 mol.%and the PVP addition is 1 wt.%,O-LAO@NCM811 positive electrode material has the highest reversible capacity and cycle stability,and the discharge capacities at 0.1,0.2,0.5,1,and 2 C are 202.6,198.8,198.0,190.1,and 180.0 m Ah/g,respectively.After200 cycles at 1 and 2 C,the discharge capacities are 165.3 and 160.1 m Ah/g,respectively.（2）Study on inorganic Al（NO₃）₃-coated Li Ni_0.8Co_0.1Mn_0.1O₂cathode material and its electrochemical performance.Inorganic Al（NO₃）₃was used as the precursor for coating to obtain I-LAO@NCM811(Inorganic Al source-derived Li Al O₂@Li Ni_0.8Co_0.1Mn_0.1O₂)microsphere cathode material.When water was used as the coating solvent,Al（NO₃）₃could hydrolyze into H⁺,which etched the surface of Ni_0.8Co_0.1Mn_0.1（OH）₂precursor microspheres,exposing more active interfaces and facilitating the uniform adsorption of Al³⁺to form a more homogeneous LAO coating layer,promoting the doping of Al³⁺in NCM811 and reducing the mixing of nickel and lithium in the lattice.In-situ test results of gas production in the battery indicated that PVP-assisted I-LAO@NCM811 cathode material could effectively suppress electrolyte decomposition and the generation of gases such as CO₂/O₂,enhancing the cycling stability of the cathode material.When the amount of Al（NO₃）₃in the water coating solution was 3 wt.%,the acid etching time was 2 h,and the PVP addition amount was 1 wt.%,the I-LAO@NCM811 cathode material exhibited the best electrochemical performance.The initial discharge capacity was as high as 211.2m Ah/g at 0.1 C,and the initial coulombic efficiency was 86%.The discharge capacities at 1,2,and 5 C were 192.7,185.5,and 174.9 m Ah/g,respectively,and the discharge capacities remained stable at 172.3,165.3,and 157 m Ah/g after 200 cycles.