Cation-anion interaction with different ratios of salt to solvent is investigated by FT-Raman spectroscopy. The fitting result of the C-N-C bending vibration manifests that the cation-anion coordination structure chan...Cation-anion interaction with different ratios of salt to solvent is investigated by FT-Raman spectroscopy. The fitting result of the C-N-C bending vibration manifests that the cation-anion coordination structure changes tremendously with the variation of salt concentration. It is well known that lithium-ion transport in ultrahigh salt concentration electrolyte is dramatically different from that in dilute electrolyte, due to high viscosity and strong cation-anion interaction. In ultrahigh salt concentrated ＂solvent-in-salt＂ electrolyte （SIS-7#）, we found, on one hand, that the cation and anion in the solution mainly formed cation-anion pairs with a high Li＋ coordination number （〉 1）, including intimate ion pairs （20.1%） and aggregated ion pairs （79.9%）, which not only cause low total ionic conductivity but also cause a high lithium transference number （0.73）. A possible lithium transport mechanism is proposed： in solvent-in-salt electrolytes, lithium ions＇ direct movement presumably depends on Li-ion exchange between aggregated ion pairs and solvent molecules, which repeats a dissolving and re-complexing process between different oxygen groups of solvent molecules.展开更多
基金supported by the National Basic Research Program of China(Grant No.2014CB932300)the National Natural Science Foundation of China(Grant Nos.51222210+1 种基金51472268,and 11234013)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA09010300)
文摘Cation-anion interaction with different ratios of salt to solvent is investigated by FT-Raman spectroscopy. The fitting result of the C-N-C bending vibration manifests that the cation-anion coordination structure changes tremendously with the variation of salt concentration. It is well known that lithium-ion transport in ultrahigh salt concentration electrolyte is dramatically different from that in dilute electrolyte, due to high viscosity and strong cation-anion interaction. In ultrahigh salt concentrated ＂solvent-in-salt＂ electrolyte （SIS-7#）, we found, on one hand, that the cation and anion in the solution mainly formed cation-anion pairs with a high Li＋ coordination number （〉 1）, including intimate ion pairs （20.1%） and aggregated ion pairs （79.9%）, which not only cause low total ionic conductivity but also cause a high lithium transference number （0.73）. A possible lithium transport mechanism is proposed： in solvent-in-salt electrolytes, lithium ions＇ direct movement presumably depends on Li-ion exchange between aggregated ion pairs and solvent molecules, which repeats a dissolving and re-complexing process between different oxygen groups of solvent molecules.
