Effects of Li ion-solvent interaction on ionic transport and electrochemical properties in highly concentrated cyclic carbonate electrolytes
Effects of Li ion-solvent interaction on ionic transport and electrochemical properties in highly concentrated cyclic carbonate electrolytes
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高浓度环状碳酸酯电解质中锂离子-溶剂相互作用对离子输运和电化学性能的影响
DOI：
10.1016/j.nocx.2021.100071
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发表时间：
2021
影响因子：
--
通讯作者：
Ueno Kazuhide
中科院分区：
文献类型：
--
作者：
Shigenobu Keisuke;Sudoh Taku;Tabuchi Mayu;Tsuzuki Seiji;Shinoda Wataru;Dokko Kaoru;Watanabe Masayoshi;Ueno Kazuhide
近年来，人们越来越重视高锂离子迁移数（tLi）和高离子电导率（σion）的电解质对实现锂二次电池快速充电的重要性。同时满足高tLi和σ离子在液体电解质中仍然是未解决的;然而，弱配位溶剂和Li盐的高浓度电解质（HCE）将有望解决这一挑战。这一想法受到Angell等人最近对超质子离子液体的研究的启发，该离子液体包含弱布朗斯特碱和超强酸;高度不稳定和可交换的H+可以在显著弱的质子接受位点之间形成。在这里，我们研究了基于氟代碳酸亚乙酯（FEC）的电解质与双（氟磺酰基）氨基锂（Li[FSA]）的弱配位，并与基于碳酸亚乙酯（EC）的电解质进行了比较。实验和计算研究表明，在基于FEC的HCE中，溶剂和离子交换更加明显，与基于EC的HCE（tLiPP= 0.53和σion= 0.84 mS cm − 1）相比，导致更高的tLiPP（0.73）和离子电导率（1.02 mS cm−1）。然而，由于FEC固有的较低还原稳定性和HCE中释放的溶剂的氧化分解，基于FEC的HCE表现出较低的电化学稳定性。尽管具有上级的传输性能，但由于电解质的副反应，具有基于FEC的电解质的Li/LiCoO 2电池在较高的电流密度下显示出较低的放电容量和较低的库仑效率。研究表明，弱的Li-溶剂相互作用可以同时增强HCE的Li和σ离子，但它们有可能牺牲电化学稳定性。
In recent research, the importance of electrolytes with high Li+transference number (tLi) and ionic conductivity (σion) has been emphasized to realize rapid charge for Li secondary batteries. Simultaneously fulfilling hightLiandσionis still unsolved in liquid electrolytes; however, highly concentrated electrolytes (HCEs) of weakly coordinating solvents and Li salts will be promising for addressing this challenge. This idea is inspired by a recent study by Angell et al. on superprotonic ionic liquids comprising a weak Brønsted base and a superacid; highly labile and exchangeable H+can be formed between significantly weak proton accepting sites. Here, we studied weakly coordinating fluoroethylene carbonate (FEC)-based electrolytes with lithium bis(fluorosulfonyl)amide (Li[FSA]) and compared with ethylene carbonate (EC)-based electrolytes. Experimental and computational studies indicated that solvent and ion exchange is more pronounced in the FEC-based HCE, resulting in highertLiPP(0.73) and ionic conductivity (1.02 mS cm−1) compared to those of the EC-based HCE (tLiPP= 0.53 andσion= 0.84 mS cm−1). However, the FEC-based HCE exhibited lower electrochemical stability due to the intrinsically lower reductive stability of FEC and the oxidative decomposition of the liberated solvent in the HCE. Despite the superior transport properties, the Li/LiCoO2cell with the FEC-based electrolyte showed lower discharge capacities and lower Coulombic efficiencies at higher current densities due to side reactions of the electrolyte. This study demonstrates that weak Li-solvent interactions can simultaneously enhancetLiandσionof HCEs, but they have the potential to sacrifice the electrochemical stability.
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