Surface And Bulk Phase Modification Of LiNiO₂ As Cathode Material For Lithium-ion Batteries

Lithium-ion batteries（LIBs）are the leading technology for electrochemical energy storage,and their cost and energy density are mainly determined by the cathode material.Among many cathode materials of lithium-ion batteries,LiNiO₂ has attracted much attention because of its high energy density and low cost.However,its commercialization is limited by serious structural degradation and rapid capacity decline during cycling.In this work,a fast ionic conductor Li₂SeO₄ coating and gradient surface Se O₃^2-/Se O₄^2-doping was simultaneously achieved by a simple wet chemical method using the reaction of SeO₂ with residual lithium on the LiNiO₂’s surface after high temperature calcination.The synergistic effect of the Li₂Se O₄ coating and the gradient surface Se O₃^2-/Se O₄^2-doping can stabilize the interface and bulk phase structure and promote Li⁺ions diffusion.The electrochemical test results showed that the Se modified Li Ni O₂（Se-LNO）has good cycling performance and rate performance when the Se O₂ dosage was 1 wt%.When cycled between2.7-4.3 V at 25°C,Se-LNO maintained capacity retention of 90.7%（73.0%for the pristine Li Ni O₂）after 100 cycles at 0.5 C and delivered a capacity of 159m Ah g^-1 at 5 C(129 m Ah g^-1 for the pristine Li Ni O₂)Mg-Se co-modified LiNiO₂（Mg-Se-LNO）was prepared by combing Mg²⁺doping with Se modification.Mg²⁺doping can further inhibit the migration of transition metal ions（TM）from the TM-O layer to the Li-O layer and reduce the Ni²⁺/Li⁺cation mixing.Thus,the Mg-Se co-modification can more effectively improve the stability of the layered structure and accelerate the diffusion of lithium ions.When chared/discharged between 2.7-4.3 V at 25°C,Mg-Se-LNO gives a capacity of 133 m Ah g^-1 at 10 C(114 m Ah g^-1 for Se-LNO)and has a capacity retention of 89.9%（67.1%for Se-LNO）after 200 cycles at0.5 C,exhibiting better cyclic stability and rate performance.Our work offers a novel strategy to improve the structural stability and the electrochemical performance of Li Ni O₂.The findings provided here can provide insights into the development of high-performance LiNiO₂ and are beneficial to the development of other layer cathodes for LIBs.