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

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journal contribution
posted on 03.06.2019, 00:00 by Ruqian Lian, Jianrui Feng, Dashuai Wang, Qifeng Yang, Dongxiao Kan, Muhammad Mamoor, Gang Chen, Yingjin Wei
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 LixVS4 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.