These solutions, which remain liquid at room temperature, enable high ion conduction and efficient, high-quality metal film formation. Despite their potential, the physicochemical or thermodynamic properties of these liquids have not been fully defined, and understanding the dissolved species and their structures remains a complex challenge.
A research team from Niigata University, led by Professor Yasuhiro Umebayashi and Dr. Jihae Han, in collaboration with Dr. Hikari Watanabe from Tokyo University of Science, has been exploring the mechanisms behind lithium-ion conduction in lithium solvate ionic liquids and highly concentrated electrolyte solutions.
Their research has led to the discovery of a novel glass-forming liquid electrolyte - a two-component mixture of cyclic sulfone and lithium salt that exhibits a glass transition over a broad compositional range. The study also delved into the dynamics of speciation and dipole reorientation to explain the high Li+ transference number observed in these mixtures. The findings were published in 'Faraday Discussions' on June 10, 2024.
The study of thermophysical properties in binary mixtures of lithium salt with 1,3-propanesultone (PS) or sulfolane (SL) revealed that a glass transition occurred only within specific lithium salt concentration ranges. Raman spectroscopy provided insights into the existence of lithium ions as contact ion pairs (CIPs) and aggregates (AGG) in solution.
Additionally, the use of two-dimensional correlation analysis of Raman spectra and dielectric relaxation spectra (DRS) helped to attribute the observed relaxation in DRS to these aggregates. This suggests that the large-scale aggregates formed at high lithium salt concentrations play a critical role in the unique lithium-ion conduction observed.
As the world aims to meet the Sustainable Development Goals (SDGs) and achieve the objectives of Society-5, there is a pressing need for next-generation energy storage devices that can efficiently store electric energy and are optimized for specific uses. The advancement of these devices, utilizing both liquid and solid electrolytes, is gaining momentum.
"Our research into glass-formed liquid electrolytes marks a significant leap towards bridging the gap between traditional liquid and solid electrolytes," explained Professor Yasuhiro Umebayashi, the corresponding author. "These materials offer unique advantages in terms of efficiency and application-specific adaptability, paving the way for next-generation energy storage devices."