Measuring and Enhancing the Ionic Conductivity of Chloroaluminate Electrolytes for Al-Ion Batteries

At the core of the aluminum (Al) ion battery is the liquidelectrolyte,which governs the underlying chemistry. Optimizing the rheologicalproperties of the electrolyte is critical to advance the state ofthe art. In the present work, the chloroaluminate electrolyte is madeby reacting AlCl3 with a recently reported acetamidiniumchloride (Acet-Cl) salt in an effort to make a more performant liquidelectrolyte. Using AlCl3:Acet-Cl as a model electrolyte,we build on our previous work, which established a new method forextracting the ionic conductivity from fitting voltammetric data,and in this contribution, we validate the method across a range ofmeasurement parameters in addition to highlighting the model electrolytes'conductivity relative to current chloroaluminate liquids. Specifically,our method allows the extraction of both the ionic conductivity andvoltammetric data from a single, simple, and routine measurement.To bring these results in the context of current methods, we compareour results to two independent standard conductivity measurement techniques.Several different measurement parameters (potential scan rate, potentialexcursion, temperature, and composition) are examined. We find thatour novel method can resolve similar trends in conductivity to conventionalmethods, but typically, the values are a factor of two higher. Thevalues from our method, on the other hand, agree closely with literaturevalues reported elsewhere. Importantly, having now established theapproach for our new method, we discuss the conductivity of AlCl3:Acet-Cl-based formulations. These electrolytes provide asignificant improvement (5-10x higher) over electrolytesmade from similar Lewis base salts (e.g., urea or acetamide). TheLewis base salt precursors have a low economic cost compared to state-of-the-artimidazolium-based salts and are non-toxic, which is advantageous forscale-up. Overall, this is a noteworthy step at designing cost-effectiveand performant liquid electrolytes for Al-ion battery applications.

Automated summary

In this study, a chloroaluminate electrolyte was made by reacting AlCl3 with Acet-Cl salt to obtain a more performant liquid electrolyte. A novel method for extracting ionic conductivity was established and compared to conventional methods. The electrolytes made with Acet-Cl showed significant improvement (5-10x higher) compared to those made with similar Lewis base salts. This study is an important step towards designing cost-effective and performant liquid electrolytes for Al-ion battery applications.