Lithiation mechanism of W18O49 anode material for lithium-ion batteries: Experiment and first-principles calculations

Tungsten-based materials are very promising anode materials for lithium-ion batteries. Their lithiation processes involve two types of reactions, intercalation and conversion reactions, which occur sequentially according to the degree of lithiation. However, the boundary between these two reactions and their effects on the overall electrochemical performance still need more in-depth understanding and description. Herein, an X-ray diffraction and first-principles calculation were combinedly implemented to reveal the lithiation processes of the monoclinic W18O49. The transformation between intercalation and conversion reactions was found to be dependent on the number of intercalated Li atoms. The in-situ XRD analysis shows structural phase transformations occurred as the deep charge-discharge was performed, which corresponding to the structure of LixW18O49 (x > 22) revealed by the first-principles calculation. Moreover, excellent stability of battery capacity was found in the shallow charge-discharge, whereas not in the deep charge-discharge. Based on this study, we comprehensively deciphered the factors that affect the electrochemical performance and reaction mechanism of W18O49 with lithium. We hope this study could contribute to the application of W18O49 and similar transition metal oxide anode materials for lithium ion batteries.