A new Mn-based layered cathode with enlarged interlayer spacing for potassium ion batteries

Layered Mn-based cathode (K_xMnO₂) has attracted wide attention for potassium ion batteries (PIBs) because of its high specific capacity and energy density. However, the structure and capacity of K_xMnO₂ cathode are constantly degraded during the cycling due to the strong Jahn-Teller effect of Mn³⁺ and huge ionic radius of K⁺. In this work, lithium ion and interlayer water were introduced into Mn layer and K layer in order to suppress the Jahn-Teller effect and expand interlayer spacing, respectively, thus obtaining new types of K_0.4Mn_1-xLi_xO₂·0.33H₂O cathode materials. The interlayer spacing of the K_0.4MnO₂ increased from 6.34 to 6.93 Å after the interlayer water insertion. X-ray photoelectron spectroscopy studies demonstrated that proper lithium doping can effectively control the ratio of Mn³⁺/Mn⁴⁺ and inhibit the Jahn-Teller effect. In-situ X-ray diffraction exhibited that lithium doping can inhibit the irreversible phase transition and improve the structural stability of materials during cycling. As a result, the optimal K_0.4Mn_0.9Li_0.1O₂·0.33H₂O not only delivered a higher capacity retention of 84.04 % compared to the value of 28.09 % for K_0.4MnO₂·0.33H₂O, but also maintained a greatly enhanced rate capability. This study provides a new opportunity for designing layered manganese-based cathode materials with high performance for PIBs.