Exceptionally stable and safe lithium-ion batteries enabled by a unique electrolyte

Lithium-ion batteries face risks associated with liquid electrolyte leakage and flammability. We have developed a flame-resistant electrolyte comprised of sulfolane, lithium bis(trifluoromethanesulfonyl)imide, and 5 wt% of 5 × 10 6 g mol −1 polyethylene oxide as a rheology modifier. The electrolyte has a low shear viscosity of ∼10 2 Pa s, and shear-thins beyond a stress of 10 2 Pa, facilitating ingress into electrode pores under shear, and subsequent immobilization. At 37°C, three 7-stack LFP|LTO pouch cells with an electrode loading of ∼18 and ∼20 mg cm −2 , respectively, show a mean capacity loss of 0.6% at 4300 cycles at 100% depth-of-charge and discharge at C/2. The cells retain 97% of their C/10 capacity at C/2 and recover their initial capacity following discharge at 8C. At 75°C, stable performance was maintained for ∼400 cycles before packaging degradation caused capacity loss. At 0°C, the cells completed 1000 cycles at C/2 with robust capacity retention. Overcharge, external short circuit and nail penetration produced short-lived surface temperature increases of 17°C, 7°C and 1°C respectively. X-ray photoelectron spectroscopy shows the formation of a thin solid electrolyte interphase layer after formation cycles and insignificant growth or composition change after cycling further. The unique electrolyte enables high endurance, safe and temperature-resilient lithium-ion cells.