Hierarchically Porous Donut‐Like Fe3Ni2Se4 Bimetallic Selenide: An Ultra‐High‐Rate Anode for Potassium Ions Storage

Abstract Transition‐metal selenides are considered as one of the promising anode materials for potassium ion batteries (PIBs) due to their high theoretical capacities. However, addressing the issue of irreversibility caused by the large volume changes during potassiation/depotassiation, especially at high rates, remains a major challenge. This challenge is tackled by constructing nickel‐iron selenide (NFS) with a unique hierarchically porous donut‐like morphology using a simple template‐free solvothermal strategy. With the bimetallic strategy and well‐designed architecture, the donut‐like NFS displays outstanding potassium storage performance, exhibiting a high reversible capacity (458 mAh g −1 even after 100 cycles at a slow rate of 0.1 A g −1 ), an impressive rate capability up to 10 A g −1 (≈10 mA cm −2 ), and an excellent capacity retention over 1000 cycles at 2 A g −1 . By combining theoretical and experimental techniques, a two‐stage intercalation‐conversion reaction mechanism is put forward. This work provides an effective approach to develop bimetallic selenides electrode materials for applications in PIBs and potentially for other energy storage devices.