Efficient Aluminum Chloride–Natural Graphite Battery

Abstract

The quest for low-cost and large-scale stationary storage of electricity has led to a surge of reports on novel batteries comprising exclusively highly abundant chemical elements. Aluminum-based systems, <i>inter</i> alia, are appealing because of the safety and affordability of aluminum anodes. In this work, we examined the recently proposed aluminum-ionic liquid-graphite architecture. Using ²⁷Al nuclear magnetic resonance, we confirmed that AlCl₄^- acts as an intercalating species. Although previous studies have focused on graphitic cathodes, we analyzed the practicality of achievable energy densities and found that the AlCl₃^-based ionic liquid is a capacity-limiting anode material. By focusing on both the graphitic cathode and the AlCl₃^-based anode, we improved the overall energy density. First, high cathodic capacities of ≤150 mAh g<SUP>-1</SUP> and energy efficiencies of 90% at high electrode loadings of at least 10 mg cm<SUP>-2</SUP> were obtained with natural, highly crystalline graphite flakes, which were subjected to minimal mechanical processing. Second, the AlCl₃ content in the ionic liquid was increased to its maximal value, which essentially doubled the energy density of the battery, resulting in a cell-level energy density of ≤62 Wh kg<SUP>-1</SUP>. The resulting batteries were also characterized by high power densities of at least 489 W kg<SUP>-1</SUP>.