Nucleation and Conversion Transformations of the Transition Metal Polysulfide VS₄ in Lithium-Ion Batteries

Transition metal polysulfides with high S content, such as VS₄, TiS₄, and MoS₃, have high specific Li⁺ capacities, but their reaction mechanisms for lithium-ion batteries remain unclear due to unknown intermediate products. In this work, first-principles calculations based on the density functional theory were performed to reveal the electrochemical properties of VS₄ for lithium-ion batteries. The results demonstrated multiple phase transformations during Li⁺ insertion, starting with nucleation transformation from VS₄ to Li₃VS₄ and followed by gradual decomposition reactions. Enthalpy-driven long-range migration of Li₂S molecules resulted in crystalline to amorphous transformation during decomposition. S and V successively behaved as redox centers for Li _xVS₄ before and after x = 3. Moreover, low activation energy and high Li⁺ diffusivity were observed at room temperature, revealing superior rate capability of the material.