Preparation And Modification Of LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Material For Lithium-ion Batteries

Nickel-rich Li Ni_0.8Co_0.1Mn_0.1O₂ is considered as one of the most promising cathode materials for electric vehicle power batteries,due to its high discharge specific capacity,and has been applied in the commercial industry.However,the poor cycling performance of Li Ni_0.8Co_0.1Mn_0.1O₂ limits its large-scale commercial applications.In this paper,the calcination conditions of Li Ni_0.8Co_0.1Mn_0.1O₂ were studied,and the electrochemical properties of the cathode material have been improved by surface coating.Cathode material Li Ni_0.8Co_0.1Mn_0.1O₂ was prepared by high-temperature solid-phase reaction,and the effects of sintering conditions on the microstructure,morphology and electrochemical properties of the prepared cathode materials were carefully analyzed by characterization and charge/discharge testing.The results showed that the optimum sintering conditions for Li Ni_0.8Co_0.1Mn_0.1O₂ were oxygen atmosphere,Li excess 5%,the sintering temperature 750°C and the sintering time 16 h.The Li Ni_0.8Co_0.1Mn_0.1O₂ prepared under this condition has well-developed layered structure and low mixing degree of cations.The first discharge specific capacity of the sample was 200.3 m Ah·g^-1 at 0.2C and the first coulombic efficiency was 87.2%.Ti O₂,Sn O₂,Zr O₂ and WO₃ were selected as the coating substances to modify Li Ni_0.8Co_0.1Mn_0.1O₂ by a wet coating.The samples were analyzed by XRD,SEM,particle size analysis,cyclic performance tests,multiplicative performance tests and CV tests.Sn O₂,Zr O₂and WO₃ can enhance the cycling performance and rate performance,and WO₃ coated sample showed the best electrochemical performance.Further study on the modification effect of different coating amounts of WO₃ showed that WO₃ forms a dense protective layer on the material.The WO₃ coating can greatly enhance the cycling performance and rate performance of Li Ni_0.8Co_0.1Mn_0.1O₂,and 1.0 wt.%WO₃ coated sample displays the best electrochemical performances.With the WO₃ modification,the capacity retention was significantly increased from 81.6%to 93.2%after 100 cycles at 1C.The discharge specific capacity 170.1 m Ah·g^-1of the samples is much higher than that of Li Ni_0.8Co_0.1Mn_0.1O₂(154.5 m Ah·g^-1)at 5C during the rate performance tests.It could be concluded that the WO₃ coating can reduce the degree of polarization during the electrochemical reaction,and inhibit side reactions for the cathode material,thus keeping structural stability of Li Ni_0.8Co_0.1Mn_0.1O₂.Li Al O₂-coated Li Ni_0.8Co_0.1Mn_0.1O₂ was prepared by a hydrolysis-hydrothermal method.The results showed that the Li Al O₂ coating effectively enhanced the first coulombic efficiency,cycling performance and rate performance of Li Ni_0.8Co_0.1Mn_0.1O₂,and the 1.0 wt.%Li Al O₂coated sample displays the best electrochemical performances.The first coulombic efficiency of the material was 89.6%at 0.2C,and the discharge specific capacity and capacity retention150.4 m Ah·g^-1 and 80.6%after 200 cycles at 1C,respectively,with improved magnification performance.The XPS,CV and EIS results showed that the Li Al O₂ coating could improve the reversibility of the electrode reaction,reduce the direct contact between the cathode material and the electrolyte,inhibit the value of R_ct growth and maintain the charge transfer ability during long cycles.