Relaxation of the Jahn–Teller stress effect in the P3-type K0.5MnO2 cathode by copper and magnesium co-substitution for high-performance K-ion batteries

The Mn-based P3-type layered oxide (K_0.5MnO₂) is a promising cathode material for K-ion batteries (KIBs) because of its low cost, high specific capacity, and simple synthesis. However, it suffers from severe capacity loss and sluggish K⁺ diffusion kinetics, which are mainly attributed to multiple phase transitions and the Jahn–Teller distortion of Mn³⁺. To address these challenges, herein, the Mg and Cu co-substitution strategy is proposed to synthesize the P3-type K_0.5Mn_0.8Mg_0.1Cu_0.1O₂ (P3-KMMCO) as a cathode for KIBs. The presence of divalent Mg²⁺ and Cu²⁺ in the crystal structure of P3-KMMCO play the critical functions in regulating the Jahn–Teller-active Mn³⁺, thereby suppressing the complex phase transitions and improving the K⁺ diffusion kinetics during charging and discharging. As a result, the P3-KMMCO cathode demonstrates the high reversible capacity, outstanding cycling stability and power capability. A combination study of synchrotron-based X-ray analysis and first-principles calculations is used to validate the enhanced electrochemical K⁺ storage properties of the P3-KMMCO cathode.