Manganese-based layered oxides for electrochemical energy storage: a review of degradation mechanisms and engineering strategies at the atomic level

Abstract

The ever-increasing demand for high-energy-density electrochemical energy storage has been driving research on the electrochemical degradation mechanisms of high-energy cathodes, among which manganese-based layered oxide (MLO) cathodes have attracted high attention thanks to their low cost and eco-friendliness. More importantly, MLO materials with large and tunable interlayer spacing are ideal candidates for the insertion of (monovalent, divalent, trivalent) alkaline ions, such as Li⁺, Na⁺, K⁺, Zn²⁺, Mg²⁺, and Al³⁺, enabling impressive electrochemical performance. Nevertheless, the local MnO₆ octahedron distortion induced by the Jahn–Teller (J–T) effect can lead to irreversible phase transformation, dissolution/disproportionation reactions, interfacial degradation arising from Mn²⁺, and crack formation, which significantly impact the electrochemical stability of MLO materials. Hence, in this review, we discuss the various degradation processes caused by J–T distortion in MLO cathodes at the atomic level. Advances in the atomic-level structure and property optimizations of MLO materials and in-depth structure–function–property correlations are also systematically reviewed. Finally, we provide our perspectives on the future development of MLO materials. The integration of high-performance MLO cathodes in energy storage devices has great potential to address growing global energy demands.