Enabling structurally and thermally stable ultrahigh‐Ni and Co‐free oxide cathodes by Nb‐dopant‐enriched surface

Abstract Inactive cation doping has demonstrated potential in stabilizing high‐capacity ultrahigh‐Ni layered oxide cathodes. Yet, maximizing their structural and thermal stability with a limited doping content remains a significant challenge. In this study, we have sought to address this challenge by regulating the distribution of cation dopants in polycrystalline material and designing a surface Nb‐dopant‐enriched ultrahigh‐Ni and Co‐free cathode. In situ X‐ray diffraction and density functional theory calculation demonstrate that surface Nb‐dopant enrichment alleviates the H2/H3 phase transition and reduces the volume shrinkage, making the absence of microcracks in the ultrahigh‐Ni cathode. Furthermore, the side reactions occurring at the electrode/electrolyte interface are mitigated, leading to a reduction in electrochemical impedance and the facilitation of stable redox contributions. The designed ultrahigh‐Ni cathode shows significantly improved structural stability and obtains an outstanding capacity retention of 97.1% even after 400 cycles, which exceeds the 66.5% capacity retention of the pristine cathode. Moreover, the enhanced thermal stability of the surface Nb‐dopant‐enriched cathode is evidenced by its higher thermal runaway temperature and lower heat release. This proposed strategy offers a feasible solution for stabilizing ultrahigh‐Ni cathodes under a low doping content.