Lithium transference in electrolytes with star-shaped multivalent anions measured by electrophoretic NMR
Lithium transference in electrolytes with star-shaped multivalent anions measured by electrophoretic NMR
复制标题
通过电泳核磁共振测量星形多价阴离子电解质中的锂转移
DOI：
10.1039/d3cp00923h
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发表时间：
2023
影响因子：
3.3
通讯作者：
Balsara, Nitash P.
中科院分区：
文献类型：
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作者：
Chakraborty, Saheli;Halat, David M.;Im, Julia;Hickson, Darby T.;Reimer, Jeffrey A.;Balsara, Nitash P.
改善电解质中锂转移的一种方法是使用大体积的多价阴离子。我们研究了一种多价盐，其中含有大星形阴离子，具有多面体低聚倍半硅氧烷（POSS）中心和溶解在溶剂中的锂抗衡离子。每个阴离子 z− 上的电荷等于 -20。所有物种的自扩散系数均通过脉冲场梯度核磁共振（PFG-NMR）测量。正如预期的那样，阴离子扩散明显慢于阳离子扩散。近似转移数（也称为电流分数）（通过 Bruce、Vincent 和 Watanabe 方法测量）高于 PFG-NMR 预期的值。然而，通过电泳核磁共振测量的严格定义的相对于溶剂速度的阳离子转移数在所有盐浓度下都是负的。相反，正如预期的那样，基于 PFG-NMR 和电流分数的近似转移数始终为正。这三种独立的锂转移表征方法之间的差异表明溶液中存在复杂的阳离子-阴离子相互作用。显然，大体积多价阴离子的缓慢自扩散并不一定会导致锂迁移的改善。
One approach for improving lithium transference in electrolytes is through the use of bulky multivalent anions. We have studied a multivalent salt containing a bulky star-shaped anion with a polyhedral oligomeric silsesquioxane (POSS) center and lithium counterions dissolved in a solvent. The charge on each anion, z−, is equal to −20. The self-diffusion coefficients of all species were measured by pulsed field gradient NMR (PFG-NMR). As expected, anion diffusion was significantly slower than cation diffusion. An approximate transference number, also referred to as the current fraction (measured by Bruce, Vincent and Watanabe method), was higher than those expected from PFG-NMR. However, the rigorously defined cation transference number with respect to the solvent velocity measured by electrophoretic NMR was negative at all salt concentrations. In contrast, the approximate transference numbers based on PFG-NMR and current fractions are always positive, as expected. The discrepancy between these three independent approaches for characterizing lithium transference suggests the presence of complex cation–anion interactions in solution. It is evident that the slow self-diffusion of bulky multivalent anions does not necessarily lead to an improvement of lithium transference.