Aguilera Luis, Scheers Johan, Matic Aleksandar
Department of Physics, Chalmers University of Technology, 412 96, Göteborg, Sweden.
Phys Chem Chem Phys. 2016 Sep 14;18(36):25458-25464. doi: 10.1039/c6cp04766a.
We investigate Li coordination in mixed electrolytes based on ionic liquids (ILs) and organic solvents and its relation with the macroscopic properties such as phase behaviour and ionic conductivity. Using Raman spectroscopy we determine the solvation shell around Li in mixtures formed by the IL N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, the organic solvents ethylene carbonate and dimethyl carbonate (EC : DMC 1 : 1), and the salt LiTFSI. We find that the organic solvent molecules preferentially solvate Li as long as there are enough of them. Our results are consistent with a model where Li(EC)(DMC) and Li(EC)(DMC) are the main complexes formed by the organic solvent molecules and where TFSI mainly participates in Li(TFSI) clusters. As the amount of organic solvent is increased, the number of TFSI around Li rapidly decreases showing a higher affinity of the organic solvents to solvate Li. The changes in the local configurations are also reflected in the ionic conductivity and the phase behaviour. The formation of larger clusters leads to a decrease in the conductivity, whereas the presence of several different clusters at intermediate compositions effectively hinders crystallization at low temperatures. The result is an enhanced low-temperature ionic conductivity in comparison with the pure IL or organic solvent electrolytes.
我们研究了基于离子液体（ILs）和有机溶剂的混合电解质中锂的配位情况，以及它与诸如相行为和离子电导率等宏观性质的关系。利用拉曼光谱，我们确定了由离子液体N-丁基-N-甲基吡咯烷鎓双（三氟甲磺酰）亚胺、有机溶剂碳酸亚乙酯和碳酸二甲酯（EC∶DMC 1∶1）以及盐LiTFSI形成的混合物中锂周围的溶剂化壳层。我们发现，只要有机溶剂分子数量足够，它们就优先使锂溶剂化。我们的结果与一个模型一致，在该模型中，Li(EC)(DMC)和Li(EC)(DMC)是由有机溶剂分子形成的主要配合物，并且TFSI主要参与Li(TFSI)簇的形成。随着有机溶剂含量的增加，锂周围TFSI的数量迅速减少，这表明有机溶剂对锂溶剂化具有更高的亲和力。局部构型的变化也反映在离子电导率和相行为上。较大簇的形成导致电导率降低，而在中间组成下几种不同簇的存在有效地阻碍了低温下的结晶。结果是与纯离子液体或有机溶剂电解质相比，低温离子电导率得到了提高。
