Enhanced potassium-ion storage performance of bimetallic-sulfide based on regulatory reaction mechanism

Developing advanced materials for reversibly accommodating K⁺ and understanding their electrochemical mechanism is essential for K⁺ storage. Herein, we report a bimetallic-sulfide with a hollow nanopyramid structure wrapped by reduced graphene oxide as an anode (NiCo_1.15S₄@rGO) for potassium ion batteries (PIBs). It is revealed that the NiCo_1.15S₄@rGO with octahedral sites can ensure reversible intercalation/deintercalation of K⁺. The irreversible phase transformation produces “death substances” during the potassium storage, leading to severe capacity degradation. In the regulated voltage window of 0.25–2.5 V, the NiCo_1.15S₄@rGO exhibited an intercalation/deintercalation reaction mechanism without irreversible phase transformation, which delivered a high reversible capacity of 436 mAh g⁻¹ at 0.5 A g⁻¹ and excellent rate properties (315 mAh g⁻¹ at 1.5 A g⁻¹). The corresponding reaction mechanisms and morphological evolution were further revealed by in-situ powder X-ray diffraction (XRD), in-situ electrochemical impedance spectroscopy (EIS), and ex-situ characterizations. An in-depth understanding of bimetallic sulfide anodes for advanced PIBs may provide decisive guidance for the design of high-performance anodes.