Surface/Interface Structure Degradation of Ni-Rich Layered Oxide Cathodes toward Lithium-Ion Batteries: Fundamental Mechanisms and Remedying Strategies

Nickel-rich layered transition-metal oxides with high-capacity and high-power capabilities are established as the principal cathode candidates for next-generation lithium-ion batteries. However, several intractable issues such as the poor thermal stability and rapid capacity fade as well as the air-sensitivity particularly for the Ni content over 80% have seriously restricted their broadly practical applications. The properties and nature of the stable surface/interface, where the Li+ shuttles back and forth between the cathode and electrolyte, play a significant role in their ultimate lithium-storage performance and industrial processability. Thus, tremendous efforts are made to in-depth understanding of the essential origins of surface/interface structure degradation and efficient surface modification methodologies are intensively explored. The purpose of the contribution is first to provide a comprehensive review of the up-to-date mechanisms proposed to rationally elucidate the surface/interface behaviors, and then, focus on recent developed strategies to optimize the surface/interface structure and chemistry including synthetic condition regulation, surface doping, surface coating, dual doping-coating modification, and concentration-gradient structure as well as electrolyte additives. Finally, the perspective on future research trends and feasible approaches toward advanced Ni-rich cathodes with stable surface/interface is presented briefly.