Srinivasan H, Sharma V K, Mukhopadhyay R, Mitra S
Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
J Chem Phys. 2020 Sep 14;153(10):104505. doi: 10.1063/5.0018510.
Lithium based deep eutectic solvents (DESs) are excellent candidates as eco-friendly electrolytes for lithium ion batteries. While some of these DESs have shown promising results, a clear mechanism of lithium ion transport in DESs is not yet established. This work reports the study on the solvation and transport of lithium in a DES made from lithium perchlorate and acetamide using Molecular Dynamics (MD) simulation and inelastic neutron scattering. Based on hydrogen bonding (H-bonding) of acetamide with neighboring molecules/ions, two states are largely prevalent: (1) acetamide molecules that are H-bonded to lithium ions (∼36%) and (2) acetamide molecules that are entirely free (∼58%). Analyzing their stochastic dynamics independently, it is observed that the long-range diffusion of the former is significantly slower than that of the latter. This is also validated from the neutron scattering experiment on the same DES system. Furthermore, the analysis of the lithium dynamics shows that the diffusion of acetamide molecules in the first category is strongly coupled to that of lithium ions. On an average, the lithium ions are H-bonded to ∼3.2 acetamide molecules in their first solvation. These observations are further bolstered through the analysis of the H-bond correlation function between acetamide and lithium ions, which shows that ∼90% of lithium ionic transport is achieved by vehicular motion where the ions diffuse along with their first solvation shell. It is also observed that the ionic motions are largely uncorrelated and the conductivity of lithium ions in the DES is found to be 11 mS/cm. The findings of this work are an important advancement in understanding solvation and transport of lithium in the DES.
基于锂的深共熔溶剂（DESs）是锂离子电池环保型电解质的理想候选材料。虽然其中一些DESs已显示出有前景的结果，但DESs中锂离子传输的明确机制尚未确立。这项工作报告了使用分子动力学（MD）模拟和非弹性中子散射对高氯酸锂和乙酰胺制成的DES中锂的溶剂化和传输的研究。基于乙酰胺与相邻分子/离子的氢键（H键），两种状态在很大程度上普遍存在：（1）与锂离子形成H键的乙酰胺分子（约36%）和（2）完全自由的乙酰胺分子（约58%）。独立分析它们的随机动力学，观察到前者的长程扩散明显慢于后者。这也通过对同一DES系统的中子散射实验得到验证。此外，对锂动力学的分析表明，第一类中乙酰胺分子的扩散与锂离子的扩散强烈耦合。平均而言，锂离子在其第一溶剂化层中与约3.2个乙酰胺分子形成H键。通过分析乙酰胺与锂离子之间的H键相关函数，进一步支持了这些观察结果，该函数表明约90%的锂离子传输是通过离子与其第一溶剂化层一起扩散的载体运动实现的。还观察到离子运动在很大程度上是不相关的，并且DES中锂离子的电导率为11 mS/cm。这项工作的发现是理解DES中锂的溶剂化和传输方面的一项重要进展。
