Cationic Point Defect Fluoride to Improve Reaction Kinetics in (All) Solid-State Li Batteries

Nickel-rich cathode materials (NCM) have emerged as promising candidates for lithium-ion batteries (LIBs) and all-solid-state batteries (ASSBs) due to their high reversible capacity (>200 mAh g^-1). However, surface side reactions with liquid and solid electrolytes during cycling increase interfacial resistance and accelerate capacity fading, thereby hindering the practical implementation of NCM cathodes. To achieve high-energy LIBs and ASSBs, it is essential to control the interfacial reactions. This can be achieved by integrating coating materials that exhibit a high ionic conductivity and excellent electrochemical stability. In this paper, we propose a cationic defect concept that leads to expansion of the Li kinetic pathway and the formation of a coherent crystal framework that induces a durable interface. This concept is implemented using Li_3+xAl_1-x/3F₆ models for reducing the interfacial resistance and enhancing the structural stability of NCM cathodes in both LIBs and ASSBs. The Li_3.3Al_0.9F₆ coating layer exhibiting high ionic conductivity and superior voltage stability effectively controls interfacial side reactions at both electrolyte interfaces, reducing interfacial resistance and improving cycling performance. It can enhance the electrochemical properties of NCM cathode materials, contributing to the realization of high-energy LIBs and ASSBs. We investigate the impact of the chemical composition of the Li_3.3Al_0.9F₆ coating layer on the reversibility and interfacial stability of NCM cathodes and further identify the effectiveness of the coating under high-temperature and high-voltage conditions. Based on the intriguing cationic defect concept, our findings contribute to the development of highly stable cathode materials for the implementation of high-energy LIBs and ASSBs.