Abstract
The electrochemical performance of aluminum-sulfur batteries is beset by poor stability and sluggish charge-storage properties. To address these issues, carbon allotropes have been used as electrode fillers, but successful outcomes remain inexplicably elusive. Here, a composite of sulfur and small-diameter single-walled carbon nanotubes was studied as a cathode for AlCl3:[EMIM]-based aluminum batteries. The presence of carbon nanotubes, while enabling a high capacity (1024 mAh g–1) with slower decay and reducing the electrolyte-to-sulfur ratio, is insufficient to fully stabilize the cell’s performance. In fact, the main obstacle is in the interaction between sulfur and chloroaluminate ions. As we show, there is a gradual buildup of insoluble and poorly conductive discharge products that inhibit the diffusion of electroactive ions and, ultimately, cause capacity decay. Overall, this work sheds light on the carbon–sulfur–electrolyte interactions and their role on the underlying charge-storage mechanism of aluminum-sulfur batteries.