Enhanced Oxygen Redox Reversibility and Structural Stability in Li 2 MnO 3 Cathode Material via High‐Entropy Stabilization

Abstract Li 2 MnO 3 , a cobalt‐ and nickel‐free layered oxide material with high theoretical capacity, is a promising candidate for next‐generation, cost‐effective cathode materials in lithium‐ion batteries. However, its practical application is hindered by severe irreversible phase transition from layered to spinel structure and oxygen loss, resulting in poor cycling performance. In this study, a high‐entropy stabilized material, Li 1.0 Na 0.2 K 0.2 Mn 0.535 Zr 0.015 Cu 0.025 Mg 0.025 O 1.7 F 0.3 (HE‐LMO), is developed to mitigate these issues. The high‐entropy design effectively stabilizes the layered structure, suppresses the formation of Mn 3 O 4 , and reduces irreversible oxygen evolution. As a result, HE‐LMO exhibits enhanced structural stability and delivers a specific capacity of ≈270 mAh g −1 after 20 cycles, attributed to the activation of reversible oxygen redox activity. Advanced characterization techniques, including X‐ray absorption spectroscopy, in situ X‐ray diffraction, and ex situ aberration‐corrected scanning transmission electron microscopy, are employed to elucidate the impact of high‐entropy stabilization on the material's performance. These findings highlight the effectiveness of high‐entropy stabilization in improving lithium‐rich manganese‐based cathode materials, providing a novel strategy for developing low‐cost, high‐performance cathode materials for lithium‐ion batteries.