Restraining the Jahn-Teller Distortion in Mn-Based Layered Cathodes toward High-Performance Potassium-Ion Batteries.

Mn-based layered oxides are regarded as a promising cathode candidate for potassium-ion batteries (PIBs) due to their high theoretical capacity and low cost. However, the cooperative Jahn-Teller distortion (CJTD) derived from six-coordinated high-spin Mn (III) (t-e) centers is a serious issue that induces severe structural instability such as irreversible phase transformations, structural degradation, and Mn dissolution, thus deteriorating their cycling life during repeated charge and discharge processes. Herein, a P3-KLiFeMnO (KLFMO) cathode material is designed to regulate CJTD and corresponding electronic structures through quantifying occupancy in the d and d orbitals of Mn. The synergistic incorporation of Li and Fe suppresses Mn (3d-e*) orbital splitting, which contributes to restrained Jahn-Teller distortion of MnO, enlarged K layer spacings, and contracted transition-metal slabs. Therefore, the detrimental phase transition from P3 to O3, local strain concentration, inhomogeneous surface structure reconstruction, and severe manganese dissolution are significantly alleviated due to the suppressed CJTD. Consequently, the target KLFMO cathode achieves a high capacity of 110.2 mA h g at 0.2C and great cycling stability with 84.2% capacity retention after 150 cycles at 0.6C. Our findings provide an effective method to develop stable 3d transition-metal compounds free from the Jahn-Teller effect for advanced secondary batteries.