Structure–Performance Correlation in K 0.5 Mn 0.5 Fe 0.5 O ₂ Cathode Optimized for Enhanced Cycling Stability and Rate Capability in Potassium-Ion Batteries

Potassium-ion batteries (PIBs) are promising for large-scale energy storage, with layered K 0.5 Mn 0.5 Fe 0.5 O 2 emerging as a competitive cathode candidate. However, its electrochemical performance is highly sensitive to solid-state synthesis parameters, which remain insufficiently optimized. This study employed a two-tiered optimization strategy combining orthogonal experimental design with single-factor investigations. A four-factor, three-level orthogonal array (L9) first screened the effects of presintering and final-sintering temperatures and durations. Range analysis identified final-sintering temperature as the most influential factor, followed by final-sintering time, presintering temperature, and presintering time, establishing preliminary optimal conditions of presintering at 500 °C for 4 h and final-sintering at 900 °C for 10 h. Subsequent single-factor experiments (750–950 °C, 8–12 h) confirmed that 900 °C yields pure P3-phase material with fine, uniform particles, while 10 h sintering promotes a highly ordered crystal structure with stable particle size (∼2.0 μm). Electrochemical tests demonstrated that the optimally synthesized material delivers an initial discharge capacity of 71.4 mAh·g –1 at 0.2C, achieves 77.2% capacity retention after 100 cycles at 0.2C, and exhibits excellent rate capability with negligible capacity decay upon cycling between 0.2 and 3C. This two-tiered optimization approach provides an effective strategy for developing high-performance layered oxide cathodes for advanced PIB applications.