A Cost Reduction Strategy for Aluminum-Polymer Batteries: The Role of Impurities within AlCl₃

The electrolyte plays a crucial role in defining the electrochemical performance of aluminum-ion batteries (AIBs), in which AlCl₃ serves as the primary ion source. This work systematically evaluates the influence of AlCl₃-sourced impurities on polyamide-based solid polymer electrolytes (SPEs), with an emphasis on both electrochemical behavior and cost efficiency. SPEs are synthesized using a polyamide matrix and an AlCl₃:Et₃NHCl ionic liquid containing excess AlCl₃. Six AlCl₃ precursors with varying purities (98%-99.999%) and costs (0.028 Euro/g-6.198 Euro/g) are employed. Electrochemical analysis reveals that the AlCl₃ purity exerts no systematic influence on key performance indicators. Reaction kinetics, aluminum stripping/plating behavior, ionic conductivity (0.19-0.21 mS cm^-1), electrochemical stability window (2.70-2.83 V), and Coulombic efficiency (98.0-99.5%) remain nearly identical across all samples. Likewise, specific capacities (28.7-43.5 mAh g^-1) and energy densities (3.3-4.5 Wh kg^-1) exhibit no clear correlation with declared impurity levels (≤2%). Instead, variations arise primarily from electrolyte formulation and cell fabrication conditions. Complementary microscopic and compositional analyses reveal no significant impurity-induced morphological or compositional differences on the Al anode surface, supporting the electrochemical findings. Cost analysis indicates that low-purity AlCl₃ (0.028 Euro/g) delivers comparable performance to high-purity salts (6.198 Euro/g), resulting in a 94% reduction in electrolyte cost and a 56% decrease in total cell cost. These findings highlight the economic viability of lower-purity AlCl₃ for scalable AIB production.