Ternary AlCl₃-Urea-[EMIm]Cl ionic liquid electrolyte for rechargeable aluminum-ion batteries

With the dramatic increase of energy demand, the rechargeable batteries are emerging requirement for electrical energy storage (EES). Here, an affordable and eco-friendly Al/graphite battery has been established using a novel ternary AlCl₃-Urea-[EMIm]Cl electrolyte. Such ternary electrolyte improves the ionic conductivity and coulombic efficiency of the Al/graphite battery. With the superior room-temperature ionic conductivity (3.4 mS cm⁻¹) of the AlCl_3: Urea: [EMIm]Cl = 13.5: 9: 0.8 electrolyte, the battery displays the discharge voltage plateaus in the range of 1.9–1.5 V and 1.5–1.0 V (vs. Al/AlCl₄⁻) and a specific discharge capacity over 60 mA h g⁻¹ upon 150 cycles with a high coulombic efficiency of 96% ± 1% at a current density of 100 mA g⁻¹. The mechanisms of intercalation/deintercalation behaviors of the AlCl₄⁻ anions are confirmed by in situ X-ray diffraction, X-ray photoelectron spectra and so on. The results based on the low-cost AlCl₃-Urea-[EMIm]Cl electrolyte offer an available approach for developing large-scale energy storage applications from inexpensive Al/graphite batteries.