Surface Lattice Modulation Stabilizes K<sub>2</sub>Mn[Fe(CN)<sub>6</sub>] Cathode for High‐Energy K‐Ion Batteries
Xunan Wang, Chongwei Gao, Shu‐Hua Zhang, Jiali Wang, Yikai Lou, Feiyu Kang, Dengyun Zhai
Abstract
Abstract Potassium‐ion batteries (PIBs) are considered as competitive candidates for energy storage applications due to their abundant resources and low cost. K 2 Mn[Fe(CN) 6 ] (KMnF) is an ideal cathode for PIBs because of its high theoretical specific energy (≈600 Wh kg −1 ). However, it suffers from severe Mn dissolution and complex phase transitions caused by Jahn–Teller distortion, resulting in rapid capacity decay. Here, a simple, controllable and universal “transition metal (TM 2+ ) ion exchange” strategy is proposed to modulate the surface lattice of KMnF, not only stabilizing the structure but also maintaining its inherent high capacity. The surface Mn 2+ is substituted by TM 2+ , including Fe 2+ , Ni 2+ , Cu 2+ , or Co 2+ , forming heterogeneous protection layer. Especially when the surface Mn 2+ is modified by redox‐active Fe 2+ , it exhibits a capacity as high as 144 mAh g −1 and considerable energy density of 560 Wh kg −1 and a remarkable capacity retention (86% after 1,000 cycles at 50 mA g −1 , and 71% after 5,000 cycles at 1,000 mA g −1 , respectively). The surface‐modified KMnF cathode proved to be effective in stabilizing the structure by preventing the Mn dissolution and formation of tetragonal phase caused by Jahn–Teller distortion. This work provides a simple and universal strategy for stabilizing high‐energy Mn‐based cathode.