The Anion Effect on Li+ Ion Coordination Structure in Ethylene Carbonate Solutions
The Anion Effect on Li+ Ion Coordination Structure in Ethylene Carbonate Solutions
复制标题
碳酸乙烯酯溶液中阴离子对锂离子配位结构的影响
DOI：
10.1021/acs.jpclett.6b01664
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发表时间：
2016
影响因子：
5.7
通讯作者：
Zheng Junrong
中科院分区：
文献类型：
--
作者：
Jiang Bo;Ponnuchamy Veerap;ian;Shen Yuneng;Yang Xueming;Yuan Kaijun;Vetere Valentina;Mossa Stefano;Skarmoutsos Ioannis;Zhang Yufan;Zheng Junrong
可充电锂离子电池是一种有吸引力的替代电源，适用于多种应用。为了优化其性能，电解质中离子的溶剂化特性的完整描述至关重要。然而，对非水碳酸盐电解质中锂离子溶剂化结构的纳米尺度的全面了解仍不清楚。我们通过飞秒振动光谱测量了不同浓度的LiBF4、LiPF6和LiClO4碳酸亚乙酯溶液中Li+结合和Li+非结合碳酸亚乙酯分子的CO伸缩模式的取向相关时间。令人惊讶的是，我们发现在所有浓度高于0.5 M的溶液中，Li+的第一溶剂化层中碳酸亚乙酯的配位数仅为2。密度泛函理论计算表明，第一配位层中阴离子的存在改变了配合物普遍接受的四面体结构，仅允许两个EC分子直接与Li+配位。据我们所知，我们的结果首次证明了阴离子对锂离子第一溶剂化壳层整体结构的影响。这种阳离子/溶剂/阴离子复合物的形成为高浓度锂/碳酸盐电解质溶液的离子电导率下降提供了合理的解释。
Rechargeable lithium ion batteries are an attractive alternative power source for a wide variety of applications. To optimize their performances, a complete description of the solvation properties of the ion in the electrolyte is crucial. A comprehensive understanding at the nanoscale of the solvation structure of lithium ions in nonaqueous carbonate electrolytes is, however, still unclear. We have measured by femtosecond vibrational spectroscopy the orientational correlation time of the CO stretching mode of Li+-bound and Li+-unbound ethylene carbonate molecules, in LiBF4, LiPF6, and LiClO4ethylene carbonate solutions with different concentrations. Surprisingly, we have found that the coordination number of ethylene carbonate in the first solvation shell of Li+is only two, in all solutions with concentrations higher than 0.5 M. Density functional theory calculations indicate that the presence of anions in the first coordination shell modifies the generally accepted tetrahedral structure of the complex, allowing only two EC molecules to coordinate to Li+directly. Our results demonstrate for the first time, to the best of our knowledge, the anion influence on the overall structure of the first solvation shell of the Li+ion. The formation of such a cation/solvent/anion complex provides a rational explanation for the ionic conductivity drop of lithium/carbonate electrolyte solutions at high concentrations.