Molecularly engineered cyclic phosphate ester as a flame-retardant electrolyte solvent for high-voltage lithium-ion batteries

Safety concerns arising from the flammability of electrolytes severely impede the broader application of lithium-ion batteries (LIBs), particularly in high energy density and large-scale energy storage. To overcome this bottleneck, this study introduced an innovative approach by designing and synthesizing a novel five-membered cyclic phosphate ester solvent to replace the flammable and unstable carbonate-based solvents used in conventional LIBs. Utilizing molecular design methods based on quantum chemical calculations, we successfully identified solvent molecules integrating the flame-retardant properties of the phosphate ester group with the film-forming advantages of the cyclic structure. Subsequently, we successfully synthesized the target novel solvent molecule through a straightforward and efficient one-step coupling reaction involving 2‑chloro‑2-oxo-1,3,2-dioxaphospholane (COP) and tetrafluoropropanol. Experimental results demonstrated that the electrolyte system formulated with this novel solvent and Lithium bis (fluorosulfonyl) imide (LiFSI) salt not only exhibited superior flame-retardant performance, significantly outperforming traditional carbonate electrolytes, but also possessed excellent high-voltage tolerance and cycling stability.