Gradient and multilevel surface modification of Ni-rich layered cathodes by gas penetration for enhanced electrochemical performance

High-capacity Ni-rich layered cathodes have sparked intense interest for application in advanced Li-ion batteries but suffer from capacity and voltage decay issues. Despite strengthening the interfacial stability to some extent, the general approach of surface modification on secondary particles still fails to resolve the critical structural degradation. Herein, we report a transformative strategy to achieve the surface modification of Ni-rich layered cathodes at both primary and secondary levels without sacrificing the Li+ insertion sites by gas penetration and in situ gas-solid reaction. The significantly improved rate capability and cycling stability of the modified cathodes are associated with the protective and conductive surface layers formed on the surface of multilevel particles, which play important roles in stabilizing the cathode-electrolyte interface, promoting Li ion diffusivity, restraining phase transformation, and preventing the formation of intergranular microcracks. This work offers a promising design strategy for advanced Ni-rich cathodes with coupling improvements of specific capacity, cycling stability, and rate capability. Gradient surface modification at both primary and secondary particle levels is achieved by gas penetration and in situ gas-solid reaction.