Microcapsule-electrolyte enabling thermal shutdown toward safe lithium metal batteries

The persistent risk of thermal runaway poses a critical challenge to the development of high-energy-density lithium metal batteries. Herein, we propose an intelligent electrolyte system embedded with a temperature-responsive thermal shutdown function to mitigate this issue. The design incorporates microencapsulated pentaerythritol tetraacrylate (PETEA), which synergistically interacts with ethylene-terminated trimethylolpropane triacrylate (ETPTA) in the electrolyte. Upon temperature elevation, the microcapsules rupture and release PETEA, triggering rapid in situ polymerization with ETPTA within four minutes. This induces a liquid-to-solid phase transition in the electrolyte, effectively blocking ion transport pathways and preventing uncontrolled exothermic reactions. Experimental results demonstrate that this modified electrolyte raises the thermal runaway onset temperature of a 1 Ah pouch cell from 140 °C to 234 °C, delaying trigger time by over six hours. In combustion tests, the peak temperature and total heat release are reduced by 67.7% and 63.6%, respectively. Simultaneously, a Li₃N-rich solid electrolyte interphase (SEI) is formed, facilitating efficient Li⁺ transport and suppressing lithium dendrite growth. The LiFePO₄//Li cell retains 92.1% capacity after 300 cycles. This work offers a simple and effective strategy toward developing high-safety, high-energy-density lithium metal batteries.