Modulating Co-Co bonds average length in Co0.85Se1_xSx to enhance conversion reaction for potassium storage

While alloying transition metal chalcogenides (TMCs) with other chalcogen elements can effectively improve their conductivity and electrochemical properties, the optimal alloying content is still uncertain. In this study, we study the influence of dopant concentration on the chemical bonds in TMC and reveal the associated stepwise conversion reaction mechanism for potassium ion storage. According to density function theory calculations, appropriate S-doping in Co0.85Se (Co0.85Se1_xSx) can reduce the average length of Co-Co bonds because of the electronegativity variation, which is thermodynamically favourable to the phase transition reactions. The optimal Se/S ratio (x = 0.12) for the conductivity has been obtained from experimental results. When assembled as an anode in potassium-ion batteries (PIBs), the sample with optimized Se/S ratio exhibits extraordinary electrochemical performance. The rate performance (229.2 mA h g_1 at 10 A g_1) is superior to the state-of-the-art results. When assembled with Prussian blue (PB) as a cathode, the pouch cell exhibits excellent performance, demonstrating its great potential for applications. Moreover, the stepwise K+ storage mechanism caused by the coexistence of S and Se is revealed by in-situ X-ray diffraction and ex-situ transmission electron microscopy techniques. Hence, this work not only provides an effective strategy to enhance the electrochemical performance of transition metal chalcogenides but also reveals the underlying mechanism for the construction of advanced electrode materials. (c) 2023 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.