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 (K0.5MnO2) 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 K0.5Mn0.8Mg0.1Cu0.1O2 (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. We introduce the Mg and Cu co-substituted P3-K0.5MnO2 (P3-KMO) cathode. This co-substitution strategy regulated the Mn oxidation state and induced the disordering within TMO2 slab, which relaxed the Jahn-Teller distortion of Mn3+ and suppressed the K+/vacancy ordering. As a result, P3-K0.5Mn0.8Mg0.1Cu0.1O2 (P3-KMMCO) cathode demonstrated continuous phase transition with sloping voltage profiles, leading to superior cycling stability and power capability. [Display omitted] •The synergy effect of Mg and Cu co-substitution suppress the Jahn-Teller distortion.•The P3-KMMCO cathode exhibits a superior cycling stability and power capability.•DFT calculations confirm suppression of Jahn-Teller distortion in P3-KMMCO cathode.