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

Layered Mn-based cathode (KMnO) has attracted wide attention for potassium ion batteries (PIBs) because of its high specific capacity and energy density. However, the structure and capacity of KMnO cathode are constantly degraded during the cycling due to the strong Jahn-Teller effect of Mn 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 KMnLiO·0.33HO cathode materials. The interlayer spacing of the KMnO 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/Mn 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 KMnLiO·0.33HO not only delivered a higher capacity retention of 84.04 % compared to the value of 28.09 % for KMnO·0.33HO, 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.