Achieving the Golden Balance between Structure and Performance via Potassium Content Regulation: Enhancing Electrochemical Properties of K _<i>x</i> Mn _0.5 Fe _0.5 O ₂ Cathode toward Potassium-Ion Batteries

Among numerous cathode materials, Mn/Fe-based oxides have demonstrated outstanding commercialization potential due to their unique two-dimensional diffusion channels and excellent structural stability. However, the structural degradation problem caused by the inherent Jahn–Teller (JT) effect of Mn 3+ has severely restricted its commercialization process. In response to this key scientific issue, in this study, the coprecipitation and solid phase composite synthesis method is adopted to successfully prepare the K x Mn 0.5 Fe 0.5 O 2 cathode material. The inhibition mechanism of it on the JT effect is deeply explored through systematically regulating the potassium content. DFT calculations demonstrate that the K 0.5 Mn 0.5 Fe 0.5 O 2 system induces electronic delocalization of Mn ions via a charge compensation mechanism, simultaneously suppresses JT distortion, and maintains optimal thermodynamic stability. The XPS test combined with the XAFS test successfully verifies the results of the theoretical calculation. Electrochemical performance tests indicate that the K 0.5 Mn 0.5 Fe 0.5 O 2 material has the best potassium storage performance. Ex-situ XRD analysis further confirm that moderate regulation of potassium content could significantly improve the structural stability of the material. This research, through the perfect fit of theoretical calculations and experimental results, provides an innovative solution and research path for breaking through the key scientific challenges of Mn/Fe-based binary potassium-ion batteries cathode materials.