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

Layered Mn-based cathode (K x MnO 2 ) 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 x MnO 2 cathode are constantly degraded during the cycling due to the strong Jahn-Teller effect of Mn 3+ 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 0.4 Mn 1-x Li x O 2 ·0.33H 2 O cathode materials. The interlayer spacing of the K 0.4 MnO 2 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 Mn 3+ /Mn 4+ 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 0.4 Mn 0.9 Li 0.1 O 2 ·0.33H 2 O not only delivered a higher capacity retention of 84.04 % compared to the value of 28.09 % for K 0.4 MnO 2 ·0.33H 2 O, 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.