Nucleation and Conversion Transformations of the Transition Metal Polysulfide VS 4 in Lithium-Ion Batteries.

Transition metal polysulfides with high S content, such as VS ₄ , TiS ₄ , and MoS ₃ , 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 VS ₄ for lithium-ion batteries. The results demonstrated multiple phase transformations during Li ⁺ insertion, starting with nucleation transformation from VS ₄ to Li ₃ VS ₄ and followed by gradual decomposition reactions. Enthalpy-driven long-range migration of Li ₂ S molecules resulted in crystalline to amorphous transformation during decomposition. S and V successively behaved as redox centers for Li _x VS ₄ 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.