Researchers from DGIST (Gyeongbuk Institute of Science and Technology, Republic of Korea) have demonstrated lithium metal battery cycling over a wide range of temperatures (2-60°C) by adopting a new dilution technique for high concentration electrolytes. Insights from the study, published in Chemical Engineering Journal, could prove useful for development of batteries for electric vehicles.

The research team led by Prof Hongkyung Lee and Hochun Lee investigated the impact of high concentration electrolyte (HCE) dilution on lithium metal battery (LMB) cycling over a wide temperature. The study showed that dilution of HCE significantly improves Li⁺ ion transport at lower temperatures and thermal stability of the solid-electrolyte interface at higher temperatures, thereby increasing the cycling performance of LMBs.

Li-metal batteries (LMBs) have very high energy density and require a fraction of time to charge when compared to their Li-ion counterparts. However, they suffer from low current efficiency, poor cyclability and are prone to Li-dendrite formation. Scientists have found that using high salt concentration electrolytes (HCE) diluted with ether-based solvents can address these problems and improve performance. However, a proper understanding of how HCE dilution affects the working of LMBs over a wide range of working temperatures is still a lingering question.

The electrolyte-deterministic interfacial stability is a crucial concern for securing battery performances. This work provides a rational strategy for diluting high-concentration electrolytes to stabilize a highly reactive Li surface. The findings in this study can offer the clues to design electrolyte microstructure, identify its fundamental impact on the interfacial stability over a wide temperature range, and contribute toward stable cycling of Li-metal batteries in practice.

—Prof Hongkyung Lee

HCEs are often viscous and diluting them can increase the ion migration within the cell and improve wetting of electrodes. The team adopted a new HCE dilution technique that allowed them to demonstrate good LMB cycling performance at temperatures between 2–60°C. The study conducted a comparative electrochemical analysis of a model HCE well as an HCE diluted with 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE).

Park et al.

The experimental results indicated that TTE dilution significantly improved Li⁺ ion transport and reduced dendritic Li plating at low temperatures, which is essential for maintaining cycling stability. TTE was also found to be responsible for the formation of the thermally stable solid-electrolyte interface that determines the high-temperature cycling ability of LMBs. The analysis also revealed that TTE dilution could also prove beneficial for the high voltage cycling of Li cells.

Resources

• Kisung Park, Youngseong Jo, Bonhyeop Koo, Hongkyung Lee, Hochun Lee (2021) “Wide temperature cycling of Li-metal batteries with hydrofluoroether dilution of high-concentration electrolyte” Chemical Engineering Journal doi: 10.1016/j.cej.2021.131889