How Low Temperature Heat Transfer Fluids Improve Localized High-Concentration Electrolytes for Lithium-Metal Batteries

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The rising deployment of portable devices and electric vehicles has accelerated the development of high energy-dense batteries and revived interest in lithium metal as an anode material in recent years. However, by employing the widely-used organic carbonate-based electrolyte formulations in lithium-metal batteries (LMBs), whisker-like Li deposits emerge during galvanostatic cycling, precipitating a rapid active material degradation.1 Consequently, researchers have shifted their focus towards novel electrolyte formulations aimed at facilitating a dense Li deposition and prolonging the cycle life of LMBs. A promising approach is the application of localized high-concentration electrolytes (LHCEs) due to their unique solvation structure, causing the formation of an effective anion-derived Solid Electrolyte Interphase (SEI) and a dense Li deposition morphology.2–5 One of the remaining challenges for this novel electrolyte concept is the low ionic conductivity and the resulting declining galvanostatic cycling performance at higher current densities (> 1 mA cm-2), thus making the increase of the ion mobility crucial to enable LHCEs to become viable electrolyte solutions for LMBs.In our study, we investigated inexpensive heat transfer fluids as effective co-diluents for LHCEs employed in LMBs. Incorporating these low-cost fluids into the electrolyte formulation results in lower viscosity and enhances molecular diversity, thereby improving transport properties and causing superior fast-charging capabilities of the resulting LMB chemistry. While the introduction of these novel co-diluents appears to have no discernible effect on the composition of the interphase layer formation, their presence promotes a more uniform lithium deposition morphology, particularly under higher charging rates. Additionally, the non-flammable nature of these components enhances the safety profile of the LMBs, rendering the novel components as multifunctional co-diluents for LHCEs and concurrently improving several crucial properties of the resulting electrolyte formulation.