Suppressing the Jahn–Teller Effect in Mn‐Based Layered Oxide Cathode toward Long‐Life Potassium‐Ion Batteries

Abstract Mn‐based layered oxides are one of the most appealing cathodes for potassium‐ion batteries (PIBs) because of their high theoretical capacity. However, the Jahn–Teller effect of Mn 3+ induces detrimental structural disorder and irreversible phase transition, leading to inferior cycling stability. Herein, an efficient strategy to suppress the Jahn–Teller effect in Mn‐based layered oxides by regulating the Mn average valence is demonstrated. To verify this strategy, Ti 4+ and Mg 2+ ions are chosen and introduced into the layered oxides (K 0.5 Mn 0.7 Co 0.2 Fe 0.1 O 2 ), which can enhance the structural stability but have opposite effects on the regulation of Mn 3+/4+ valence. The K 0.5 Mn 0.6 Co 0.2 Fe 0.1 Mg 0.1 O 2 with a higher Mn valence (4+) exhibits long‐term cycling stability as a PIB cathode compared to the K 0.5 Mn 0.6 Co 0.2 Fe 0.1 Ti 0.1 O 2 with a lower Mn valence (3.667+). Meanwhile, the detrimental phase transition from P3 to O3 caused by Jahn–Teller effect is completely suppressed, and is replaced by a highly reversible single‐phase solid solution reaction for K 0.5 Mn 0.6 Co 0.2 Fe 0.1 Mg 0.1 O 2 . The enhanced cycling stability and single‐phase reaction are attributed to the suppressed Jahn–Teller effect via Mn valence regulation, confirmed by first‐principles calculations. Therefore, this discovery paves the way for the development of advanced layered cathodes for the next‐generation high‐performance PIBs.