P3-Type KCoMgMnO as a superior cathode material for potassium-ion batteries with high structural reversibility ensured by Co-Mg Co-substitution

Mn-based layered oxides, as potential cathodes for potassium-ion batteries (PIBs), face major challenges such as consecutive phase transition, serious capacity loss, and sluggish K + transport kinetics. Herein, Co-Mg co-substituted K 0.45 Co 1/12 Mg 1/12 Mn 5/6 O 2 is designed as a promising cathode material for PIBs to conquer the above issues in this work. Co 3+ -Mg 2+ ions occupying the Mn 3+ sites are confirmed to effectively alleviate the Jahn-Teller distortion induced by Mn 3+ ions. P3-K 0.45 Co 1/12 Mg 1/12 Mn 5/6 O 2 exhibits highly reversible single-phase structural evolution during the K + deintercalation/intercalation. In contrast, the pristine K 0.45 MnO 2 electrode experiences incompletely reversible structural variation from a P′3 to P3 phase. The increase of structural stability in the Co-Mg co-substituted sample is the main reason leading to improved cycling stability. Moreover, K 0.45 Co 1/12 Mg 1/12 Mn 5/6 O 2 delivers better rate capability resulting from faster K + diffusion compared to K 0.45 MnO 2 . Therefore, Co-Mg co-substitution is an effective strategy to enhance the structural stability and electrochemical properties of Mn-based layered oxides in PIBs. P3-K 0.45 Co 1/12 Mg 1/12 Mn 5/6 O 2 exhibits highly reversible single-phase structural evolution during the K + deintercalation/intercalation. On the contrast, the pristine K 0.45 MnO 2 electrode experiences incompletely reversible structural variation from a P′3 to P3 phase.