High-Efficiency Fire-Suppressive Coatings for Li-Ion Batteries: Mitigating Thermal Runaway without Sacrificing Electrochemical Performance

Abstract

Fire and explosion accidents caused by thermal runaway of lithium-ion batteries (LIBs) have seriously hindered the development of their high-energy-density applications. Herein, we designed and synthesized a novel ZIF-67@COF hybrid material and incorporated it into an epoxy resin (EP) matrix to prepare a composite coating for passive thermal protection of LIBs. By in situ growth of a covalent organic framework (COF) on the surface of aminated ZIF-67 via a solvothermal method, a ZIF-67@COF flame retardant with a heterogeneous interface was successfully constructed. With the addition of 5 wt % ZIF-67@COF, the peak heat release rate (PHRR) and total smoke production (TSP) of the EP composite were significantly reduced by 38.5% and 19.4%, respectively, compared with neat EP, demonstrating an excellent synergistic flame-retardant effect of condensed-phase char formation and gas-phase radical scavenging. When the optimized ZIF-67@COF coating was applied onto the surface of commercial 103450 batteries, thermal runaway tests showed that a 100 μm-thick coating delayed the thermal runaway onset temperature from 200.1 to 240.2 °C, extended the voltage drop onset time from 929 to 1014 s, greatly suppressed flame intensity, and effectively blocked propagation of chain thermal runaway. Importantly, further systematic electrochemical performance evaluation (including charge–discharge cycling at various rates and 200-cycle long-term cycling stability tests) confirmed that the introduction of this flame-retardant coating did not produce any detectable negative effects on capacity retention, Coulombic efficiency, or interfacial charge transfer process of the battery, demonstrating excellent compatibility between thermal safety protection and electrochemical performance. This multilevel synergistic flame-retardant mechanism, combined with its excellent compatibility with the battery’s electrochemical performance, makes the developed EP/ZIF-67@COF coating a highly promising thermal protection solution for next-generation high-safety, high-energy-density LIBs.