Room Temperature Chloroaluminate Ionic Liquid Analogues (ILAs) for an Aluminium-Ion Battery

Chloroaluminate-based ILAs have been a promising alternative electrolyte for an aluminium-ion battery (AIB). But, since 1-ethyl-3-methylimidazolium chloride (EMIM) is very expensive, another low-cost alternative Lewis Base such as Urea has been proposed.

One of the challenges in chloroaluminate-based ILAs is to measure its conductivity. This challenge is regarded to its reproducibility of its conductivity value using commercial probe due to its high corrosive affecting the performance of the probe itself. Extracting the conductivity of the electrolytes from the voltammogram of cyclic voltammetry has been successfully conducted. It was found that the employment of voltammetry-based conductivity assessment yields conductivity values that are approximately twice the value of those obtained through the alternate two methodologies, a commercial probe and electrochemical impedance spectroscopy (EIS) probe. It is noteworthy that the magnitudes of these values align closely, and notably, the novel approach also demonstrates analogous conductivity trends when correlated with compositional data.

A new AlCl3:Guanidine Hydrochloride has been successfully electrochemical tested for AIB systems. Among the various examined compositional ratios (1.75:1, 2.00:1, 2.25:1 and 2.50:1). By using Electrochemical Quartz Crystal Microbalance (EQCM), it was found that the ratio of 2.00:1 exhibited a slope that closely approached the anticipated theoretical slope for aluminium (0.093 μg mC−1). Consequently, this specific ratio was chosen for subsequent exploratory procedures including Linear Sweep Voltammetry (LSV), Potentiodynamic Polarization, and battery performance evaluations. Both LSV and Potentiodynamic Polarization methodologies unveiled indications of a passivation layer forming on the electrode surface. Concurrently, the battery testing phase displayed notable efficacy in terms of charging/discharging capacity and coulombic efficiency. A comparative study between Guanidine-, Acetamidine-, and Urea-based electrolytes has been conducted. Both AlCl3:Guanidine and AlCl3:Acetamidine electrolytes exhibited enhanced rheological attributes encompassing conductivity, viscosity, and activation energy, outperforming the AlCl3:Urea system. Furthermore, these two electrolytic systems demonstrated more favourable conditions for the deposition of an aluminium and displayed heightened stability within the anodic realm, a factor contributing positively to battery performance. The elevated conductivity, coupled with reducedvi scosity and activation energy, translated into superior coulombic efficiencies for both electrolytes: 98.12% for AlCl3:Guanidine and 97.10% for AlCl3:Acetamidine, compared to the 88.17% observed for the AlCl3:Urea system.