RESUMEN
The thermal runaway issue represents a long-standing obstacle that retards large-scale applications of lithium metal batteries. Various approaches to inhibit thermal runaway suffer from some intrinsic drawbacks, either being irreversible or delayed thermal protection. Herein, this work has explored thermo-responsive lower critical solution temperature (LCST) ionic liquid-based electrolytes, which provides reversible overheating protection for batteries with warning and shut-down stages, well corresponding to an initial stage of thermal runaway process. The batteries could function stably below 70 °C as a working mode, while demonstrating a warning mode above 80 °C with a noticeable reduction in specific capacitance to delay temperature increase of batteries. In terms of 110 °C as a critically dangerous temperature, a shut-down mode is designed to minimize the thermal energy releasing as the batteries are barely chargeable and dischargeable. Dynamically growing polymeric particles above LCST contributed to such an intelligent and mild control on specific capacitance. Larger size will occupy larger surfaces of electrodes and close more pores of separators, enabling a gradual suppressing of Li+ transfer and reactions. The present work demonstrated a scientific design of thermoresponsive LCST electrolytes with a superiorly precise and intelligent control of electrochemical performances to achieve self-adapted overheating protections.
RESUMEN
Exploring advanced strategies in alleviating the thermal runaway of lithium-metal batteries (LMBs) is critically essential. Herein, a novel electrolyte system with thermoresponsive characteristics is designed to largely enhance the thermal safety of 1.0 Ah LMBs. Specifically, vinyl carbonate (VC) with azodiisobutyronitrile is introduced as a thermoresponsive solvent to boost the thermal stability of both the solid electrolyte interphase (SEI) and electrolyte. First, abundant poly(VC) is formed in SEI with thermoresponsive electrolyte, which is more thermally stable against lithium hexafluorophosphate compared to the inorganic components widely acquired in routine electrolyte. This increases the critical temperature for thermal safety (the beginning temperature of obvious self-heating) from 71.5 to 137.4 °C. The remained VC solvents can be polymerized into poly(VC) as the battery temperature abnormally increases. The poly(VC) can not only afford as a barrier to prevent the direct contact between electrodes, but also immobilize the free liquid solvents, thereby reducing the exothermic reactions between electrodes and electrolytes. Consequently, the internal-short-circuit temperature and "ignition point" temperature (the starting temperature of thermal runaway) of LMBs are largely increased from 126.3 and 100.3 °C to 176.5 and 203.6 °C. This work provides novel insights for pursuing thermally stable LMBs with the addition of various thermoresponsive solvents in commercial electrolytes.