Unraveling and regulating superstructure domain dispersion in lithium-rich layered oxide cathodes for high stability and reversibility

Abstract

Lithium-rich layered oxides (LLOs) have attracted tremendous attention as promising high-energy cathode materials thanks to their superb capacity through additional anionic oxygen redox. The unique cationic superstructure ordering in the Li-rich domains is responsible for triggering the characteristic anionic oxygen redox; however, the aggregated Li-rich domains lead to excessive oxidation of lattice oxygen, resulting in irreversible oxygen release and structural breakdown. Here, we probe the chemical and structural evolution during the conventional synthesis of Co-free Li-rich cathodes in real time to understand the formation of the superstructure domains. Comprehensive examinations through a suite of advanced analysis tools reveal an overlooked role of lithium sources that manipulates the solid-state synthetic pathway, and thus dictates the evolution of the superstructure domain crystallography of the resulting Li-rich cathodes. We suggest that promoted synthetic reactions with the use of lithium hydroxide monohydrate render the formation of Li-rich domain-dispersed structure which enhances the electrochemical reversibility of LLO cathodes by mitigating the structural degradation from over-oxidation of lattice oxygen. The present study provides fundamental insights into regulating homogeneities in chemical and structural properties of synthetic intermediates upon calcination to achieve highly stable and reversible Li-rich cathodes towards broader market penetration.