Insights into the Storage Mechanism of Layered VS2 Cathode in Alkali Metal-Ion Batteries

VS2 is one of the attractive layered cathodes for alkali metal-ion batteries. However, the understanding of the detailed reaction processes and energy storage mechanism is still inadequate. Herein, the Li+/Na+/K+ insertion/extraction mechanisms of VS2 cathode are elucidated on the basis of experimental analyses and theoretical simulations. It is found that the insertion/extraction behavior of Li+ is partially irreversible, while the insertion/extraction behavior of Na+/K+ is completely reversible. The detailed intermediates and final products (Li0.33VS2, LiVS2, Na0.5VS2, NaVS2, K0.6VS2, KzVS2, z > 0.6) during the discharging/charging processes are identified, indicating that VS2 undergoes different phase transitions and solid-solution reactions in different battery systems, which have a great influence on the battery performance. Moreover, the diffusion of Na+ in VS2 cathode is demonstrated to be much slower than that of Li+ and K+. Such mechanistic research provides a reference for in-depth understanding of energy storage in layered transition metal sulfides/selenides.