Comprehensive Understanding of Elemental Doping and Substitution of Ni-Rich Cathode Materials for Lithium-Ion Batteries via In Situ Operando Analyses

This review explores the challenges and advancements in the development of high-energy lithium-ion batteries (LIBs), particularly focusing on the electrochemical and structural stability of Ni-rich cathode materials. Despite their potential to increase the energy density of LIBs, these cathode materials encounter issues such as irreversible phase transitions and structural degradation during cycling, which ultimately affect their electrochemical performance. Elemental doping/substitution has emerged as promising strategies to address these challenges. However, the precise mechanisms underlying their performance enhancement remain unclear. The objective is to elucidate the complex reaction mechanisms triggered by doping and substitution in Ni-rich cathode materials by employing in situ operando analyses to uncover their effects on electrochemical behavior and structural integrity during cycling. This comprehensive investigation aims to clarify the roles of elemental dopants or substituents in the crystal structures of Ni-rich cathode materials, thereby offering valuable insights for the structural engineering of cathode materials in high-energy LIBs. By elucidating these intricate mechanisms, this review provides a practical roadmap for future research and significantly contributes to LIB technology by guiding material design and optimization strategies in the development of advanced LIBs.