A fluorinated bifunctional additive achieving stable electrode/electrolyte interfaces for high-voltage lithium-metal batteries

Abstract

Nickel-rich ternary cathodes are highly favored for lithium metal batteries due to their high energy density and operating voltage. However, challenges such as interfacial side reactions, thermal instability, and capacity degradation persist at high temperatures and elevated cut-off voltages. To address these issues, we developed a novel fluorine-containing additive, 1-methyl-3-(2,2,2-trifluoroethyl)-1,3-dihydro-2H-imidazol-2-one (M-3FEn-IO), specifically tailored for high-voltage lithium-metal batteries. Structurally analogous to the film-forming agent vinylene carbonate, M-3FEn-IO substitutes an oxygen atom with nitrogen and introduces fluorine groups at nitrogen sites, ensuring effective film formation on both electrodes. The fluorine-derived lithium fluoride (LiF) generated by M-3FEn-IO strengthens the electrode/electrolyte interfaces, markedly improving cell cycling performance. Incorporating 0.2 vol% M-3FEn-IO into carbonate-based electrolytes improved Li‖NCM622 cells, achieving 84.07% capacity retention after 600 cycles at 30 °C and 73.8% at 60 °C and a 2C rate. This work establishes a multifunctional electrolyte additive strategy to advance lithium metal battery performance.