Study On Modifacation Of Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Material For Lithium-ion Battery

In recent years,lithium-ion batteries have been greatly developed due to the advantages of clean and high efficiency.Combining with the advantages of LiNiO2,LiCoO2 and LiMnO2,the layered ternary cathode materials(LiNi2-x-yCoxMnyO2,0<x<1,0<y<1)have been extensively studied.Among them,the Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode material is considered one of the most competitive cathode materials for lithium-ion batteries for use in next-generation electric vehicles due to the high capacity.However,the poor cycle stability of layered Ni-rich cathode materials at high voltages(>4.3 V)has hindered their commercial development.In this work,we coated LiNi0.8Co0.1Mn0.1O2 cathode material with Li2O-2B2O3 to improve the high-voltage cycling performance.First,the LiNi0.8Co0.1Mn0.1O2 cathode material with a high discharge specific capacity was prepared by a solid phase method,but its cycle stability was found to be poor.Then,we coated LiNi0.1Co0.1Mn0.1O2 cathode material with Li2O-2B2O3 to reduce the corrosion of the electrolyte on the surface of the material and suppress the phase transition as much as possible,which greatly improved the high-voltage cycle stability of LiNi0.8Co0.1Mn0.1O2 cathode material at high voltage.The main work is as follows:(1)LiNi0.8Co0.1Mn0.1O2 cathode material was prepared by high temperature solid phase method with Ni0.8Co0.1Mn0.1O2(OH)2 as precursor and LiOH·H2O as lithium source.XRD shows that the material is a layered structure with a lower degree of cation mixing.The SEM characterization showed that the microstructure of the material was spherical secondary particles with a diameter of about 10 ?m and the lattice fringes were clearly observed under a high-resolution transmission microscope.In the voltage range of 2.75-4.5 V and at 0.1 C(18 mA g-1)current density,the initial discharge capacity of LiNi0.8Co0.1Mn0.1O2 cathode material is 202.5 mAh g-1 and the corresponding coulombic efficiency is 85.7%;In the same voltage range,the discharge capacity of LiNi0.8Co0.1Mn0.1O2 cathode material decreased from 189.1 mAh g-1 to 96.0 mAh g-1 after 100 cycles at 1 C(180 mA g-1)current density,the retention rate is only 50.8%.Therefore,the cycle stability under high pressure needs to be further improved.(2)The surface of LiNi0.8Co0.1Mn0.1O2 was coated with different mass ratios of Li2O-2B2O3 by liquid phase method with LiOH·H20 as lithium source and H3BO3 as the boron source.The crystal structure of the coated material was investigated using XRD.The microstructure of the coated material was investigated by SEM,EDS Mapping and TEM.The electrochemical properties of the coated material were tested by an electrochemical workstation and the optimum coating dose was determined to be 0.3%.After 100 cycles at the voltage range of 2.75-4.5V,the capacity retention of the 0.3%Li20-2B2O3 coated electrode material increased from 50.8%to 82.1%.Since the surface coating of Li2O-2B2O3 can reduce the corrosion of the electrolyte on the surface of the positive electrode material,which also suppress the transformation of surface phase and reduce the charge transfer resistance during the cycling,then improve the cycle stability of the material.In addition,the coating of 0.3%Li2O-2B2O3 can greatly improve the rate performance of LiNi0.1Co0.1Mn0.1O2 cathode material.