Dual Interphase Layers In Situ Formed on a Manganese-Based Oxide Cathode Enable Stable Potassium Storage

Mn-based oxides have attracted extensive attention as electrode materials. However, the irreversible phase transition and Mn2+ dissolution result in their structure instability and performance decay. Here, we report dual interphase layers in situ formed on P2-K0.67MnO2 (P2-KMO) in 6.0 M of potassium bis(fluorosulfonyl)amide in diglyme (KFSI/G2) during charging. It is composed of a solid-electrolyte interphase (SEI) and K-poor spinel interlayer on P2-KMO, which are derived from the simultaneous decomposition of 6.0 M KFSI/G2 and disproportionation of surface Mn3+. They cooperatively enable the reversible phase transition of P2↔P″2 in the bulk P2-KMO and mitigate Mn loss. This leads to a high capacity retention of 90.5% and a Coulombic efficiency of 100% after 300 cycles. The investigation highlights the significance of interphase chemistry of electrode materials for potassium-ion batteries and beyond.