Peculiarly Fast Li-ion Conduction Mechanism in a Succinonitrile-Based Molecular Crystal Electrolyte: A Molecular Dynamics Study
Peculiarly Fast Li-ion Conduction Mechanism in a Succinonitrile-Based Molecular Crystal Electrolyte: A Molecular Dynamics Study
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丁二腈基分子晶体电解质中异常快速的锂离子传导机制：分子动力学研究
DOI：
10.1039/d1ta02809j
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Yoshitaka Tateyama
中科院分区：
文献类型：
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作者：
Ryoma Sasaki;Makoto Moriya;Yuki Watanabe;Kazunori Nishio;Taro Hitosugi;Yoshitaka Tateyama
Li{N（SO 2F）2}（NCCH 2CH 2CN）2（Li（FSA）（SN）2）分子晶体由于具有约100 nm的高锂离子电导率而被实验报道为全固态锂离子电池应用的有希望的固体电解质。室温下为10−4 S cm−1，活化能（Ea）极低，为28 kJ mol−1。然而，快速导电机制仍然无法解释，因为所有的锂离子都被保持在晶体框架中，并且组成锂离子之间的距离对于跳跃来说太长了。在此，分子动力学（MD）模拟进行澄清的机制，非常快的锂离子导电丁二腈（SN）为基础的分子晶体。原子分子动力学模拟结果表明，Li（FSA）（SN）2晶体中Li离子空位可以稳定存在，并产生一维Li离子跳跃路径，而非传统的三维路径.计算的Ea为34 kJ mol−1，与实验值非常一致，这基本上支持一维传导。低Ea与SN分子的运动密切相关。空位处的两个SN分子改变它们的构象，随后其中一个SN分子产生负电性区域，而另一个SN分子通过摆动运动将相邻的Li离子携带到负电性区域。本研究对有机基团的行为和锂离子导电性的认识将促进高导电性分子晶体的发展。
Li{N(SO2F)2}(NCCH2CH2CN)2 (Li(FSA)(SN)2) molecular crystals have been experimentally reported as a promising solid electrolyte for all-solid-state Li-ion battery applications because of their high Li-ion conductivity of ca. 10−4 S cm−1 at room temperature and an exceptionally low activation energy (Ea) of 28 kJ mol−1. However, the fast conduction mechanism remains unexplained because all the Li-ions are held in the crystal framework, and the distances between the constituent Li-ions are too long for hopping. Herein, molecular dynamics (MD) simulations were performed to clarify the mechanism of the extraordinarily fast Li-ion conduction in the succinonitrile (SN)-based molecular crystals. Atomistic MD simulations revealed that Li-ion vacancies can exist stably in Li(FSA)(SN)2 crystals and give rise to the one-dimensional Li-ion hopping pathway contrary to the conventional scenario in which the fast conduction is attributed to the three-dimensional pathway. The calculated Ea of 34 kJ mol−1 is in good agreement with the experimental value, which substantially supports the one-dimensional conduction. The low Ea is intimately connected with the motion of the SN molecules. Two SN molecules at the vacancy site change their conformation, following which one of the SN molecules creates an electronegative region, while the other carries the adjacent Li-ion to the electronegative region by the swing motion. The insights on the behavior of organic moieties and Li-ion conduction obtained from this study will promote the development of highly conductive molecular crystals.