Insights into the doping functions on redox chemistry of layered Ni-rich cathodes

Abstract

In pursuit of low cost and long life for lithium-ion batteries in electric vehicles, the most promising strategy is to replace the commercial LiCoO₂ with a high-energy-density Ni-rich cathode. However, the irreversible redox couples induce rapid capacity decay, poor long-term cycling life, vast gas evolution, and unstable structure transformations of the Ni-rich cathode, limiting its practical applications. Element doping has been considered as the most promising strategy for addressing these issues. However, the relationships between element doping functions and redox chemistry still remain confused. To clarify this connection, this review places the dynamic evolution of redox couples (Li⁺, Ni²⁺/Ni³⁺/Ni⁴⁺-e⁻, O²⁻/Oⁿ⁻/O₂-e⁻) as the tree trunk. The material structure, degradation mechanisms, and addressing element doping strategies are considered as the tree branches. This comprehensive summary aims to provide an overview of the current understanding and progress of Ni-rich cathode materials. In the last section, promising strategies based on element doping functions are provided to encourage the practical application of Ni-rich cathodes. These strategies also offer a new approach for the development of other intercalated electrode materials in Na and K-based battery systems.