Multiple Redox Modes in the Reversible Lithiation of High-Capacity, Peierls-Distorted Vanadium Sulfide
Multiple Redox Modes in the Reversible Lithiation of High-Capacity, Peierls-Distorted Vanadium Sulfide
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DOI：
10.1021/jacs.5b03395
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发表时间：
2015-07-08
影响因子：
15
通讯作者：
Grey, Clare P.
中科院分区：
文献类型：
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作者：
Britto, Sylvia;Leskes, Michal;Grey, Clare P.
硫化钒（VS4）是一种由二硫阴离子[S-2]（2-）配位的钒原子组成的线性链式化合物。V-51核磁共振表明，尽管材料在d(1)构型中具有V，但它是抗磁性的，这表明通过与线性链的佩尔斯畸变相关的金属键可能发生二聚化。这得到了密度泛函计算的支持，也与观察到的沿链的2.8和3.2埃的V - V距离交替一致。部分锂化导致二硫离子通过内部氧化还原过程还原为硫化物S2-，在V4+氧化为V5+和[S-2]（2-）还原为S2-的过程中，来自V4+的电子转移到[S-2](2-)，形成含有四面体[VS4]（3-）阴离子的Li3VS4。在进一步的锂化过程中，Li3VS4中的V5+被还原成Li3+xVS4 (x = 0.5-1)，这是一种混合价的V4+/V5+化合物。最终还原为Li2S +单质V。尽管在这种材料中发生了复杂的氧化还原过程，包括阳离子和阴离子，但该系统在0和3 V之间是部分可逆的。利用一套短程表征工具，包括V-51核磁共振波谱（NMR）、ks边缘x射线吸收近边缘波谱（XANES）和x射线数据的对分布函数（PDF）分析，阐明了该体系中不寻常的氧化还原过程。
Vanadium sulfide VS4 in the patronite mineral structure is a linear chain compound comprising vanadium atoms coordinated by disulfide anions [S-2](2-). V-51 NMR shows that the material, despite having V formally in the d(1) configuration, is diamagnetic, suggesting potential dimerization through metal metal 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 V distances of 2.8 and 3.2 angstrom along the chains. Partial lithiation results in reduction of the disulfide ions to sulfide S2-, via an internal redox process whereby an electron from V4+ is transferred to [S-2](2-) in oxidation of V4+ to V5+ and reduction of the [S-2](2-) to S2- to form Li3VS4 containing tetrahedral [VS4](3-) anions. On further lithiation this is followed by reduction of the V5+ in Li3VS4 to form Li3+xVS4 (x = 0.5-1), 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 V-51 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.