Chemists have discovered a new glass-forming liquid electrolyte that shows impressive lithium-ion conductivity. They investigate the chemical composition and the dynamics of dipole reorientation in this electrolyte using Raman and dielectric relaxation spectroscopy, helping to further developments in battery electrolyte research.
As we move toward a more sustainable future, creating advanced electrochemical devices, such as rechargeable batteries with higher energy capacities and improved electrodeposition processes, has become increasingly important. Recently, ultra-concentrated electrolyte solutions have captured interest. These solutions involve dissolving metal salts at concentrations two to three times higher than what a single solvent can typically hold, or using mixtures where metal salts are significantly dissolved in one solvent.
These innovative solutions remain in liquid form at room temperature, providing excellent ion conductivity and allowing for efficient metal film formation of high quality. However, defining these liquids from a physicochemical or thermodynamic standpoint is still unclear. Moreover, recognizing the dissolved species and comprehending their structures—both essential for electrolyte applications—poses significant challenges.
A team from Niigata University, led by Prof. Yasuhiro Umebayashi and Dr. Jihae Han, together with Dr. Hikari Watanabe from Tokyo University of Science, has been exploring the mechanisms behind specific lithium-ion conduction in lithium solvate ionic liquids and highly concentrated electrolyte solutions from a perspective of solution chemistry. They identified a new glass-forming liquid electrolyte, which is a two-component mixture of cyclic sulfone and lithium salt, exhibiting a broad range of glass transition. To uncover the reason for the remarkably high Li+ transference number in these mixtures, they analyzed speciation and dipole reorientation dynamics, highlighting the presence of large aggregate formations. Their results were published in the Faraday Discussions on June 10, 2024.
The thermophysical properties of mixtures containing lithium salt-1,3-propanesultone (PS) and lithium salt-sulfolane (SL) demonstrated that glass transition occurred only within a specific range of lithium salt concentrations. Raman spectroscopy indicated that, in solution, lithium ions exist as contact ion pairs (CIPs) and aggregates (AGG). Furthermore, a two-dimensional correlation analysis of the Raman spectra along with dielectric relaxation spectra (DRS) indicated that the observed relaxation in DRS could be linked to the presence of AGGs created at high lithium salt concentrations, which play a significant role in lithium-ion conduction.
To meet the Sustainable Development Goals (SDGs) and the aims of Society-5, there’s an increasing demand for next-generation energy storage systems capable of efficiently storing electrical energy and designed for particular applications. The advancements in the development of these systems have enhanced the utilization of both liquid and solid electrolytes.
