In Situ Polymerized Composite Electrolytes with Multifunctional Additives for Stable and Flame-Retardant Lithium-Metal Batteries

In this study, we report an in situ polymerized composite solid electrolyte (CSE) system by impregnating poly(ethylene glycol) methyl ether acrylate (PEGMEA) into a porous PVDF-HFP matrix containing Li 6.5 Ga 0.2 La 2.95 Rb 0.05 Zr 2 O 12 (Ga-Rb LLZO). To improve thermal stability, ionic conductivity, and interfacial stability, triethyl phosphate, fluoroethylene carbonate (FEC), and succinonitrile (SN) were introduced as functional additives. The optimized formulation (IP-TFS) exhibited a high ionic conductivity of 0.741 mS·cm −1 and a lithium transference number of 0.898 at 70 °C, along with a tensile strength of 7.77 MPa. Flame retardancy was confirmed via flame tests. 19 F nuclear magnetic resonance and X-ray photoelectron spectroscopy analyses demonstrated that FEC enhanced LiF formation, contributing to stable interfacial layers, while SN facilitated lithium-ion transport. The IP-TFS electrolyte delivered stable cycling over 600 h in Li symmetric cells and >79% capacity retention over 300 cycles in LFP cells. Furthermore, pouch cells using IP-TFS maintained 92.89% capacity after 200 cycles and survived mechanical abuse. These results demonstrate that the PEGMEA-based in situ CSE, reinforced by functional additives, is a promising platform for safe and high-energy lithium-metal batteries.