Co/Al Co-Substituted Layered Manganese-Based Oxide Cathode for Stable and High-Rate Potassium-Ion Batteries

Manganese-based layered oxides are promising cathode materials for potassium-ion batteries (PIBs) due to their low cost and high theoretical energy density. However, the Jahn-Teller effect of Mn³⁺ and sluggish diffusion kinetics lead to rapid electrode deterioration and a poor rate performance, greatly limiting their practical application. Here, we report a Co/Al co-substitution strategy to construct a P3-type K_0.45Mn_0.7Co_0.2Al_0.1O₂ cathode material, where Co³⁺ and Al³⁺ ions occupy Mn³⁺ sites. This effectively suppresses the Jahn-Teller distortion and alleviates the severe phase transition during K⁺ intercalation/de-intercalation processes. In addition, the Co element contributes to K⁺ diffusion, while Al stabilizes the layer structure through strong Al-O bonds. As a result, the K_0.45Mn_0.7Co_0.2Al_0.1O₂ cathode exhibits high capacities of 111 mAh g^-1 and 81 mAh g^-1 at 0.05 A g^-1 and 1 A g^-1, respectively. It also demonstrates a capacity retention of 71.6% after 500 cycles at 1 A g^-1. Compared to the pristine K_0.45MnO₂, the K_0.45Mn_0.7Co_0.2Al_0.1O₂ significantly alleviates severe phase transition, providing a more stable and effective pathway for K⁺ transport, as investigated by in situ X-ray diffraction. The synergistic effect of Co/Al co-substitution significantly enhances the structural stability and electrochemical performance, contributing to the development of new Mn-based cathode materials for PIBs.