Preparation And Electrochemical Performance Of LiNi_0.815Co_0.15Al_0.035O₂ Cathode Materials Modified By B³⁺ Doping And WO₃ Coating

Lithium-ion batteries are widely used in industrial and portable electronics due to it being the most popular electrochemical energy storage device.It has also been widely studied for its high operating voltage,high energy density,long cycle life and low price.Among all components of lithium-ion batteries,cathode material is one of the most critical parts that determine the overall energy density and cost of the battery system.Among many cathode materials,high nickel ternary materials are considered as one of the most worthy materials to be developed and studied due to their high capacity and low cost.Li Ni_0.815Co_0.15Al_0.035O₂（NCA）,as one of the high nickel materials,has more stable Al-O bonds and shows better cycling performance.However,NCA materials face the problems of capacity loss in long cycling cycles and side reactions during charging and discharging,which limit the further application of NCA cathode materials.In order to improve the electrochemical performance of NCA cathode materials,this work modified the NCA cathode materials by B³⁺doping and WO₃surface coating,respectively.Firstly,the NCA materials were prepared by high temperature solid phase method and high speed ball milling method under different synthesis processes.X-ray diffraction analysis（XRD）results showed that the samples prepared at calcination temperature of 800°C,calcination time of20 h,and lithium proportion of 1:1.03 had a good layered structure and a low degree of Li-Ni mixing in the layered structure.The electrochemical performance of the material under this condition was as follows:the first discharge specific capacity at 0.1 C current density was 181.48m Ah/g,and the first discharge specific capacity at 1 C current density was 159.65 m Ah/g,with a capacity retention rate of 88.46%after 200 cycles.Secondly,to further improve the cycling stability of NCA cathode materials,B³⁺-doped NCA cathode materials were prepared by high-temperature solid-phase method.The results showed that the overall performance of the material was excellent at the doping amount of 1.5%.1.5%B-NCA cathode material exhibited good cycling performance due to the doping enhanced the lithium ion diffusion rate of the material.The first discharge specific capacity of 1.5%B-NCA material was178.31 m Ah/g,and the capacity retention rate was 98.87%after 100 cycles at a current density of0.2 C,which was 10.41%higher than that of the original NCA cathode material.After a high current density 5 C discharge and then back to 0.1 C discharge again,the capacity recovery rate was as high as 98.63%.Finally,to investigate the effects of WO₃coating on the structure and electrochemical performance of the NCA cathode material,the NCA cathode material was modified with different mass fractions of WO₃coating.The WO₃coating can prevent the direct contact between the active material and the electrolyte,reduce the interfacial impedance value between the NCA material and the electrolyte,and thus improve the lithium ion migration rate.The results show that the overall performance of the 2wt%coated modified NCA cathode material is excellent,and the first discharge specific capacity is 174.96 m Ah/g with a Coulomb efficiency 79.34%in a charge/discharge test at 1 C current density,and the capacity retention rate reaches 89.10%after200 cycles,which is significantly improved.This indicates that the WO₃coating is an effective way to enhance the energy density and improve the cycling performance of NCA cathode materials.