Molinari Nicola, Mailoa Jonathan P, Kozinsky Boris
John A. Paulson School of Engineering and Applied Sciences , Harvard University , Cambridge , Massachusetts 02138 , United States.
Research and Technology Center , Robert Bosch LLC , Cambridge , Massachusetts 02142 , United States.
J Phys Chem Lett. 2019 May 16;10(10):2313-2319. doi: 10.1021/acs.jpclett.9b00798. Epub 2019 Apr 25.
We show that strong cation-anion interactions in a wide range of lithium-salt/ionic liquid mixtures result in a negative lithium transference number, using molecular dynamics simulations and rigorous concentrated solution theory. This behavior fundamentally deviates from that obtained using self-diffusion coefficient analysis and explains well recent experimental electrophoretic nuclear magnetic resonance measurements, which account for ion correlations. We extend these findings to several ionic liquid compositions. We investigate the degree of spatial ionic coordination employing single-linkage cluster analysis, unveiling asymmetrical anion-cation clusters. We formulate a way to compute the effective lithium charge and show that lithium-containing clusters carry a negative charge over a remarkably wide range of compositions and concentrations. This finding has significant implications for the overall performance of battery cells based on ionic liquid electrolytes. It also provides a rigorous prediction recipe and design protocol for optimizing transport properties in next-generation highly correlated electrolytes.
我们通过分子动力学模拟和严格的浓溶液理论表明，在多种锂盐/离子液体混合物中，强阳离子-阴离子相互作用会导致负的锂迁移数。这种行为从根本上偏离了使用自扩散系数分析所得到的结果，并且很好地解释了最近考虑离子相关性的实验性电泳核磁共振测量结果。我们将这些发现扩展到几种离子液体组成。我们采用单链聚类分析研究空间离子配位程度，揭示了不对称的阴离子-阳离子簇。我们制定了一种计算有效锂电荷的方法，并表明含锂簇在非常广泛的组成和浓度范围内都带有负电荷。这一发现对基于离子液体电解质的电池单元的整体性能具有重要意义。它还为优化下一代高度相关电解质中的传输特性提供了严格的预测方法和设计方案。
