A shear-thickening fluid based on ionic liquid as dual-safe electrolyte for lithium batteries

The development of lithium-ion batteries have been obstacled by the frequent safety accidents caused by spontaneous combustion and car crash in recent years. Once lithium batteries are impacted by external mechanic forces, internal short circuit will be caused and heat will quickly accumulate inside, leading to the oxidation and decomposition of the electrolyte and thermal runaway. In this work, series of “non-combustible, impact-resistant” dual-safe electrolytes are fabricated by replacing the carbonate solvent of commercial electrolyte with non-flammable ionic liquids ([BMIM]BF₄) and introducing SiO₂ nanoparticles as fillers to improve shear thickening properties. The as-prepared shear-thickening electrolyte (STE) shows responsive thickening to high shear stress owing to the formation of SiO₂ aggregates. Compared with the carbonate solvent in commercial electrolyte, the ionic liquid solvent provides BF₄⁻ solvation layer formed by hydrogen bonds, which confines and stabilizes the SiO₂ aggregates to achieve decreased critical shear rate and higher thickening ratio. Among the STEs with varied SiO₂ fractions, the STE-20.0 shows the best overall performance of low critical shear rate (1.43 s⁻¹), high thickening ratio (89.0) and high ionic conductivity (3.63 × 10⁻³ S cm⁻¹) at room temperature. The assembled LiFePO₄||Li cell delivers a stable capacity of 150 mAh/g for 100 cycles at 0.1C and 120 mAh/g at 0.5C. In the safety tests, the STE-20.0 shows nonflammability and superior impact resisitance of 1.4 J comparing to non-SiO₂ electrolytes (0.4 J). Overall, our work demonstrates feasible and facile preparation of shear-thickening fluid as safe electrolyte for lithium-ion batteries.