A sustained-release strategy of fluorinated solvents enables highly safe lithium metal batteries

Abstract

The practical deployment of lithium metal batteries (LMBs) is hindered by the electrolyte's flammability, high heat release, and poor interfacial stability. Although fluorinated solvents contribute to interfacial stability and enhanced thermal safety, the low polarizability of fluorine atoms weakens intermolecular forces, leading to rapid volatilization and diminished flame-retardant performance. In this study, we propose a sustained-release strategy termed “molecular anchoring and thermoresponsive polymer encapsulation”. This strategy significantly enhances the flame-retardant efficiency of 2,2,2-trifluoroethyl carbonate (FEMC) during thermal runaway. Compared to 1 M LiPF₆–FEMC, in the electrolyte based on the proposed strategy volatilization can be curtailed by approximately 78.8%, and the peak volatilization rate can be decreased by 1.71%/°C. Accelerating rate calorimetry (ARC) tests indicate that the application of the sustained-release strategy effectively improves the thermal safety of the battery. For commercial electrolytes, the onset temperature of thermal runaway (T_tr) ranges from 128.4 °C to 206.8 °C, while the maximum exothermic temperature (T_max) ranges from 546.3 °C to 329.1 °C, and the peak heating rate ranges from 107.2 °C s⁻¹ to 59.8 °C s⁻¹. This study suggests that the sustained-release strategy of fluorinated solvents provides new insights for the development of high-safety batteries.