Binary Transition Metal Synergy Optimizing Redox Reversibility of Potassium-Ion Batteries.

Iron-based sulfides are promising candidates as anode in potassium-ion rechargeable batteries due to their high specific capacity, the abundant and low-cost iron sources, and environmental friendliness. However, issues like volume expansion, poor redox reversibility, and poor ion conductivity severely hinder the electrochemical performance during charging and discharging processes. To address these challenges, this work induced transition metals nickel and cobalt to construct a bimetallic co-enhanced anode of iron-based sulfide. Different schemes of calcination processes were designed, enabling the fabrication of all six types of composites of different calcination temperatures. Electrochemical tests reveal that the bimetallic synergy notably improves the redox reaction kinetics through structural regulation. Binary transition metal synergy facilitates potassium salt di-intercalation, reduces interfacial resistance, and improves ionic conductivity. It was found that the introduction of element cobalt and the calcination process notably enhanced the stability of the anode materials, while the incorporation of nickel greatly improved their specific capacity. Notably, the cobalt-introduced anode exhibited favorable potassium storage performance, retaining high specific capacity after cycling, indicating potential for practical application. This study highlights a versatile strategy for advancing stable, high-performance iron-based sulfide anodes of potassium-ion rechargeable batteries.