Electrochemical properties of Al/vanadium chloride batteries with AlCl₃-1-Ethyl-3-methylimidazolium chloride electrolyte

We have studied the electrochemical properties of vanadium chloride in molten salt containing AlCl₃ and 1-ethyl-3-methylimmidazolium chloride (EMIC) with a molar ratio of 1.5/1.0 at an ambient temperature using cyclic voltammetry and the X-ray absorption near-edge structure (XANES). Cyclic voltammograms (CVs) of VCl₃ contain a pair of oxidation peak at about 1.5 V vs. Al/Al³⁺ and reduction peak at about 0.9 V vs. Al/Al³⁺ assigned to the V(3) V(2) reaction and a pair of oxidation peak at about 0.9 V vs. Al/Al³⁺ and reduction peak at about 0.4 V vs. Al/Al³⁺ assigned to the V(2) V(0) reaction. The former remains in the CV after reduction and oxidation cycling. On the other hand, the latter disappears from the CV after a couple of cycles. We also investigate the effect of adding fluorobenzene (FB) to the AlCl₃-EMIC salts on the solubility and electrochemical properties of VCl₃. FB greatly reduces the VCl₃ dissolution in the salts and improves capacity retention with reduction and oxidation cycling without change in the reaction process.