Multiple Redox Modes in the Reversible Lithiation of High-Capacity, Peierls-Distorted Vanadium Sulfide

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• 作者：Sylvia Britto ; Michal Leskes ; Xiao Hua ; Claire-Alice H茅bert ; Hyeon Suk Shin ; Simon Clarke ; Olaf Borkiewicz ; Karena W. Chapman ; Ram Seshadri ; Jaephil Cho ; Clare P. Grey
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：July 8, 2015
• 年：2015
• 卷：137
• 期：26
• 页码：8499-8508
• 全文大小：578K
• ISSN：1520-5126

文摘

Vanadium sulfide VS₄ in the patronite mineral structure is a linear chain compound comprising vanadium atoms coordinated by disulfide anions [S₂]^{2鈥?/sup>. 51V NMR shows that the material, despite having V formally in the d1 configuration, is diamagnetic, suggesting potential dimerization through metal鈥搈etal bonding associated with a Peierls distortion of the linear chains. This is supported by density functional calculations, and is also consistent with the observed alternation in V鈥揤 distances of 2.8 and 3.2 脜 along the chains. Partial lithiation results in reduction of the disulfide ions to sulfide S2鈥?/sup>, via an internal redox process whereby an electron from V4+ is transferred to [S₂]2鈥?/sup> resulting in oxidation of V4+ to V5+ and reduction of the [S₂]2鈥?/sup> to S2鈥?/sup> to form Li₃VS₄ containing tetrahedral [VS₄]3鈥?/sup> anions. On further lithiation this is followed by reduction of the V5+ in Li₃VS₄ to form Li_3+xVS₄ (x = 0.5鈥?), a mixed valent V4+/V5+ compound. Eventually reduction to Li₂S plus elemental V occurs. Despite the complex redox processes involving both the cation and the anion occurring in this material, the system is found to be partially reversible between 0 and 3 V. The unusual redox processes in this system are elucidated using a suite of short-range characterization tools including 51V nuclear magnetic resonance spectroscopy (NMR), S K-edge X-ray absorption near edge spectroscopy (XANES), and pair distribution function (PDF) analysis of X-ray data.}