On the concentration polarisation in molten Li salts and borate-based Li ionic liquids
On the concentration polarisation in molten Li salts and borate-based Li ionic liquids
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熔融锂盐和硼酸盐基锂离子液体中的浓差极化
DOI：
10.1039/d2cp05710g
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发表时间：
2023
影响因子：
3.3
通讯作者：
Ueno Kazuhide
中科院分区：
文献类型：
--
作者：
Shigenobu Keisuke;Philippi Frederik;Tsuzuki Seiji;Kokubo Hisashi;Dokko Kaoru;Watanabe Masayoshi;Ueno Kazuhide
仅传输Li离子的电解质在提高Li二次电池的快速充电和放电性能方面起着至关重要的作用。单Li离子传导可以通过液体材料如含有Li+作为唯一阳离子的Li离子液体来实现，因为无溶剂的熔融Li盐在电化学电池中不极化，这是由于不存在允许盐浓度极化的中性溶剂以及在阴离子阻断条件下电池中不可避免的均匀密度。然而，我们发现，硼酸盐基锂离子液体诱导浓度极化的Li/Li对称的细胞，这导致在阴离子阻断条件下（tabcLi）的迁移（运输）数远低于统一。硼酸基锂离子液体的电化学极化归因于阴离子中可交换的B-O配位键在电极/电解质界面产生锂盐和硼酸酯溶剂引起的平衡移动。通过比较含不同配体的硼酸盐锂离子液体，发现B-O键强度和配体交换程度与tabcLi值直接相关。该研究证实了动态可交换键的存在导致电化学极化，并为旨在实现单离子导电液体电解质的Li离子液体的合理分子设计提供了参考。
Electrolytes that transport only Li ions play a crucial role in improving rapid charge and discharge properties in Li secondary batteries. Single Li-ion conduction can be achieved via liquid materials such as Li ionic liquids containing Li+ as the only cations because solvent-free fused Li salts do not polarise in electrochemical cells, owing to the absence of neutral solvents that allow polarisation in the salt concentration and the inevitably homogeneous density in the cells under anion-blocking conditions. However, we found that borate-based Li ionic liquids induce concentration polarisation in a Li/Li symmetric cell, which results in their transference (transport) numbers under anion-blocking conditions (tabcLi) being well below unity. The electrochemical polarisation of the borate-based Li ionic liquids was attributed to an equilibrium shift caused by exchangeable B–O coordination bonds in the anions to generate Li salts and borate-ester solvents at the electrode/electrolyte interface. By comparing borate-based Li ionic liquids containing different ligands, the B–O bond strength and extent of ligand exchange were found to be directly linked to the tabcLi values. This study confirms that the presence of dynamic exchangeable bonds causes electrochemical polarisation and provides a reference for the rational molecular design of Li ionic liquids aimed at achieving single-ion conducting liquid electrolytes.