Flame-Retardant Gel Electrolyte toward High-Safety Lithium Metal Batteries with High-Mass-Loading Cathodes

Gel electrolytes are an important transitional state in developing lithium-ion conductors from the liquid state to the solid state. However, very few gel electrolytes have been realized to enable the long-term operation of high-safety lithium metal batteries (LMBs) with high-mass-loading cathodes. Here, we propose a dual-salt gel electrolyte with a flame-retardant plasticizer (denoted as PVC/TEP electrolyte) for LMBs. Flame-retardant molecules were encapsulated into the PVC matrix via in situ polymerization of a vinylene carbonate monomer. The resultant PVC/TEP electrolyte possesses a high ionic conductivity of ∼3.1 × 10–3 S cm–1 at 30 °C, a wide electrochemical window of ∼4.85 V, and low self-extinguishing times of less than 0.3 s g–1 due to the homogeneous distribution of flame-retardant and fluorine-rich dual salts. Consequently, gel electrolyte-based LMBs with high-mass-loading cathodes (8.49 mg cm–2) achieve comparable rate performance to liquid electrolyte-based LMBs and long cycle life well beyond them.