Electrochemical potassium/lithium-ion intercalation into TiSe2: Kinetics and mechanism

As one promising candidate for next-generation energy storage systems, K-ion batteries (KIBs) attract increasing research attention due to the element abundance, low cost, and competent energy density as compared to Li-ion batteries. However, developing practical electrode materials in particular cathodes for KIBs is still in its infancy, and the related reaction mechanisms of the electrode materials are far from completely understood. In this work, TiSe2 was, for the first time, investigated as an intercalated-type electrode for potassium storage due to its large interlayer space. The potassiation/depotassiation reaction mechanism was unraveled based on the analysis of in-situ X-ray diffraction (XRD), ex-situ X-ray photoelectron spectroscopy (XPS), and ex-situ transmission electron microscope (TEM) results. Meanwhile, the lithium storage behaviour and the relevant lithiation/delithiation reaction mechanism were also studied in detail. The results reveal that K+ show lower diffusion coefficient and hence more sluggish intercalation reaction kinetics as compared with Li+. In addition, the intercalation reaction of K+ would cause irreversible structure changes, while the intercalation reaction is fully reversible for Li+ counterpart.