Entropy-Driven Multi-Ion Synergy: Building Charge and Component Gradient, Stabilizing Dynamic Structure, and Suppressing Phase Transition in Low-Cost Mn-Based Layered Cathode toward Potassium-Ion Batteries

Potassium-ion batteries (PIBs) have emerged as promising alternatives to lithium-ion batteries (LIBs), owing to the analogous physicochemical properties between K- and Li-ion. Among the diverse cathode candidates, Mn-based layered oxides have garnered considerable attention for PIB applications. However, such cathodes typically suffer from intrinsic structural instability and undesirable phase transitions during cycling. Herein, these challenges are addressed through a compositionally complex doping strategy, which draws inspiration from the high-entropy concept and leverages the synergistic effects of five distinct cations. This multication synergy mitigates the adverse impacts associated with high-level single-cation doping in K 0.5 MnO 2 (KMO) cathodes, endowing the material with superior structural stability and effectively suppressing phase evolution during cycling, thereby enhancing both cycling stability and rate capabilities. As a proof-of-concept, the designed K 0.5 Mn 0.8 Ti 0.04 Al 0.04 Fe 0.04 Cu 0.04 Zn 0.04 O 2 (HD-2) cathode delivers a discharge capacity of approximately 100 mAh g –1 in the 1.5–3.9 V range at 10 mA g –1, with 78% capacity retention over 100 cycles. This performance outperforms that of single-ion doped cathodes with an equivalent total doping content. In-situ X-ray diffraction (XRD) measurements demonstrate that undesired phase evolution is substantially suppressed, with minimal variation in the lattice parameter c, indicative of enhanced structural stability during cycling. In-situ electrochemical impedance spectroscopy (EIS) elucidates the dynamic evolution mechanism of the cathode, while ex-situ X-ray absorption fine structure (XAFS) analyses confirm that Mn ions dominate the charge compensation process. This work offers valuable insights for the rational design of high-performance Mn-based layered oxide cathodes for PIBs.