Schulz A, Lunkenheimer P, Loidl A
Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86135 Augsburg, Germany.
J Chem Phys. 2021 Jul 28;155(4):044503. doi: 10.1063/5.0055493.
Lithium-salt-based deep eutectic solvents, where the only cation is Li, are promising candidates as electrolytes in electrochemical energy-storage devices, such as batteries. We have performed broadband dielectric spectroscopy on three such systems, covering a broad temperature and dynamic range that extends from the low-viscosity liquid around room temperature down to the glassy state approaching the glass-transition temperature. We detect a relaxational process that can be ascribed to dipolar reorientational dynamics and exhibits the clear signatures of glassy freezing. We find that the temperature dependence of the ionic dc conductivity and its room-temperature value also are governed by the glassy dynamics of these systems, depending, e.g., on the glass-transition temperature and fragility. Compared to the previously investigated corresponding systems, containing choline chloride instead of a lithium salt, both the reorientational and ionic dynamics are significantly reduced due to variations in the glass-transition temperature and the higher ionic potential of the lithium ions. These lithium-based deep eutectic solvents partly exhibit significant decoupling of the dipolar reorientational and the ionic translational dynamics and approximately follow a fractional Debye-Stokes-Einstein relation, leading to an enhancement of the dc conductivity, especially at low temperatures. The presented results clearly reveal the importance of decoupling effects and of the typical glass-forming properties of these systems for the technically relevant room-temperature conductivity.
基于锂盐的低共熔溶剂，其唯一的阳离子为Li，是电化学储能装置（如电池）中很有前景的电解质候选材料。我们对三种此类体系进行了宽带介电谱研究，涵盖了从室温附近的低粘度液体到接近玻璃化转变温度的玻璃态的宽广温度和动态范围。我们检测到一个弛豫过程，该过程可归因于偶极重取向动力学，并呈现出玻璃态冻结的明显特征。我们发现离子直流电导率的温度依赖性及其室温值也受这些体系的玻璃态动力学支配，例如取决于玻璃化转变温度和脆性。与先前研究的含氯化胆碱而非锂盐的相应体系相比，由于玻璃化转变温度的变化和锂离子较高的离子势，重取向动力学和离子动力学均显著降低。这些基于锂的低共熔溶剂部分呈现出偶极重取向动力学和离子平移动力学的显著解耦，并大致遵循分数德拜 - 斯托克斯 - 爱因斯坦关系，从而导致直流电导率提高，尤其是在低温下。所呈现的结果清楚地揭示了解耦效应以及这些体系典型的玻璃形成特性对于技术上相关的室温电导率的重要性。
