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

Abstract

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 (NiCo1.15S4@rGO) for potassium ion batteries (PIBs). It is revealed that the NiCo1.15S4@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 NiCo1.15S4@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.