Progress, Challenge, and Prospect of LiMnO2: An Adventure toward High‐Energy and Low‐Cost Li‐Ion Batteries

Lithium manganese oxides are considered as promising cathodes for lithium-ion batteries due to their low cost and available resources. Layered LiMnO₂ with orthorhombic or monoclinic structure has attracted tremendous interest thanks to its ultrahigh theoretical capacity (285 mAh g^-1 ) that almost doubles that of commercialized spinel LiMn₂ O₄ (148 mAh g^-1 ). However, LiMnO₂ undergoes phase transition to spinel upon cycling cause by the Jahn-Teller effect of the high-spin Mn³⁺ . In addition, soluble Mn²⁺ generates from the disproportionation of Mn³⁺ and oxygen release during electrochemical processes may cause poor cycle performance. To address the critical issues, tremendous efforts have been made. This paper provides a general review of layered LiMnO₂ materials including their crystal structures, synthesis methods, structural/elemental modifications, and electrochemical performance. In brief, first the crystal structures of LiMnO₂ and synthetic methods have been summarized. Subsequently, modification strategies for improving electrochemical performance are comprehensively reviewed, including element doping to suppress its phase transition, surface coating to resist manganese dissolution into the electrolyte and impede surface reactions, designing LiMnO₂ composites to improve electronic conductivity and Li⁺ diffusion, and finding compatible electrolytes to enhance safety. At last, future efforts on the research frontier and practical application of LiMnO₂ have been discussed.