Identifying the nanostructure of residual Li in high-Ni cathodes for lithium-ion batteries

Abstract

With the increasing demand for higher energy density in lithium-ion batteries (LIBs), designing high-Ni cathodes with maximized Ni content is becoming essential. This pursuit leads to an increase in surface residual Li compounds (Li₂CO₃ and LiOH), triggering notorious issues such as severe side reactions, gas evolution, and the necessity for additional manufacturing processes. However, an understanding of the residual Li chemistry is still lacking. In this study, the presence of residual Li compounds in both the primary and secondary particle levels in conventional polycrystalline high-Ni cathodes was investigated. Residual Li compounds exist in a crystalline phase not only on the surfaces of secondary particles, but also within the intergranular pores between the primary particles. The identification of residual Li implies that designing and controlling the intergranular pores in high-Ni cathodes is necessary. Finally, post-treatment strategies aimed at controlling residual Li compounds in high-Ni cathodes are proposed and the characteristics of each strategy are described.