Transport and Electrochemical Properties and Spectral Features of Non-Aqueous Electrolytes Containing LiFSI in Linear Carbonate Solvents

Lithium bis(fluorosulfonyl)imide (LiFSI) has been investigated as a conducting salt of liquid electrolytes for lithium-ion batteries. It shows high solubility in most polar solvents, and a concentration of 5 M (mol dm(-3)) is reached in dimethyl carbonate (DMC) despite its low dielectric constant. LiFSI shows a thermal stability up to 180 degrees C on the thermogravimetric test. Compared with the LiPF6/carbonate electrolytes, the LiFSI-based ones show higher ionic conductivities over a wide temperature range (-50 to 50 degrees C) and higher lithium-ion transference numbers (t(Li+)) of 0.5-0.6. The conductivities of the LiFSI/DMC electrolyte over the 0.1-5 M concentration range obey a modified Casteel-Amis equation. The temperature dependence of 1 M LiFSI/DMC/EMC (3:7, v/v) is governed by the Vogel-Tammann-Fulcher relationship. The Fourier transform infrared spectra of the LiFSI/DMC electrolytes at different concentrations are systematically investigated. DMC shows significant spectral variations upon adding LiFSI, indicating strong interaction of Li+ cations with the solvent molecules. We also found that the compatibility with graphite anode and LiFePO4 cathode in the LiFSI-based electrolyte is as good as that in the LiPF6-based one, though aluminum (Al) corrosion occurs above 4 V vs Li+/Li. LiFSI is a very good contender to replace the latter, with increased performances and safety. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3514705] All rights reserved.

双（氟磺酰）亚胺锂（LiFSI）作为锂离子电池液态电解质的导电盐已被研究。它在大多数极性溶剂中具有高溶解度，尽管碳酸二甲酯（DMC）的介电常数较低，但在其中仍能达到5M（摩尔/立方分米）的浓度。在热重分析测试中，LiFSI显示出高达180℃的热稳定性。与LiPF₆/碳酸酯电解质相比，基于LiFSI的电解质在较宽的温度范围（-50℃至50℃）内具有更高的离子电导率，锂离子迁移数（t(Li⁺)）也更高，为0.5 - 0.6。LiFSI/DMC电解质在0.1 - 5M浓度范围内的电导率符合修正的卡斯蒂尔 - 艾姆斯（Casteel - Amis）方程。1M LiFSI/DMC/EMC（3:7，体积比）的温度依赖性符合沃格尔 - 塔曼 - 富勒（Vogel - Tammann - Fulcher）关系。系统地研究了不同浓度的LiFSI/DMC电解质的傅里叶变换红外光谱。加入LiFSI后，DMC显示出明显的光谱变化，表明Li⁺阳离子与溶剂分子有强烈的相互作用。我们还发现，基于LiFSI的电解质与石墨负极和磷酸铁锂（LiFePO₄）正极的相容性与基于LiPF₆的电解质一样好，尽管在相对于Li⁺/Li高于4V时会发生铝（Al）腐蚀。LiFSI是替代后者的一个很好的选择，具有更高的性能和安全性。（C）2010电化学学会。[DOI: 10.1149/1.3514705]保留所有权利。