Leakage-Free and Non-Flammable High-Safety Li Metal Battery Using 85.3 wt.% Multifunctional Organic Lithium Salt as Quasi-Solid Electrolyte

Safety issues of lithium metal batteries caused by leakageable, inflammable, and unstable electrolytes and lithium dendrites are a major concern worldwide. Herein, an ultra-concentrated electrolyte composed of 85.3 wt.% of a novel phosphate quaternary ammonium lithium salt (PQ-3Li) in fluoroethylene carbonate is prepared, labeled as CPQE. CPQE reveals an exceptional ionic conductivity (0.32 × 10⁻³ S cm⁻¹), a high lithium transference number (0.66), an electrochemical stability window above 6 V, and a superb fire resistance. Li|CPQE|Li cells show stable cycling performance without lithium dendrites for 1000 h, and a solid-electrolyte-interface layer with an inorganics-rich inner layer and an organics-rich outer layer is confirmed using computation simulation, electron probe microanalysis, and X-ray photoelectron spectroscopy. Li|CPQE|NCM cells present a discharge capacity of 162 mAh g⁻¹ at 0.1 C, and a Coulombic efficiency of up to 99%. A commercial LED bulb can be lighted up by the Li|CPQE|NCM cell for at least 1 h without performance deterioration while prolonging the cycling time. The fabricated CPQE-based pouch cells own terrific safety and power supply capacity. No leakage, thermal runaway, combustion, or explosion behavior is detected during the nailing penetration test, implying large potential applications for developing the next generation of high-safety lithium batteries.