Low‐Viscosity Solvent‐Assisted Non‐Flammable Deep Eutectic Electrolyte Enhances Thermal Stability and Energy Density of Li/CF x Batteries

Abstract Non‐flammable deep eutectic electrolytes (DEEs) have emerged as promising candidates for addressing the safety concerns in secondary batteries. However, their high viscosity and strong Li + ‐solvent interactions result in sluggish ion transport, leading to severe capacity degradation and limiting their practical application in lithium/fluorinated carbon (Li/CF x ) primary batteries. Herein, a novel non‐flammable and low‐viscosity deep eutectic electrolyte (DEE‐DME) is proposed for the first time to enhance the thermal stability and overall electrochemical performance of Li/CF x batteries. In particular, N‐methylacetamide (NMAC) serves as a hydrogen bond donor, promoting lithium salt dissociation and eutectic formation, while suppressing the crystallinity of discharge products, lithium fluoride (LiF), to yield smaller LiF particles. The addition of low‐viscosity dimethoxyethane (DME) improves electrolyte wettability, enhances ionic conductivity (13.03 mS cm −1 ), and modulates Li⁺ solvation structure (anion coordination enhanced and solvent coordination weakened), thereby accelerating ion transport kinetics. Notably, the designed DEE‐DME exhibits intrinsic non‐flammability, along with a short self‐extinguishing time (≈1 s g −1 ). The assembled Li/CF x batteries employing DEE‐DME deliver a high energy density of 961.2 Wh kg −1 at 6000 mA g −1 at room temperature, together with low self‐discharge after seven days at 50 °C. This electrolyte design offers a significant step forward in enabling intrinsically safe, high‐performance Li/CF x batteries.