Towards understanding aluminum sulfur batteries with imidazolium-based electrolytes: A phenomenological model

Aluminum sulfur batteries with ionic liquid electrolytes are promising next-generation energy storage devices due to the high abundance of both aluminium and sulfur. However, very little understanding of the discharge mechanism is currently available, which hampers their development. Herein, a mathematical model that considers the complex electrochemical reduction of the sulfide species as well as the formation of the various polysulfides is developed to describe the discharge performance and the reversibility of Al–S cells at different current densities. The model is validated with experimental data obtained from Swagelok cells composed of Al metal anode, S@CNT cathode, and EMIMCl-AlCl₃ ionic liquid electrolyte. The cells exhibited different discharge mechanisms and Al₂S₃ precipitation routes at the different current densities. The contact resistance between the composite electrode and the current collector was the main factor limiting the discharge performance at high current densities. The reversibility of the Al–S cells based on the formation of Al₂S₃ precipitates strongly depends on the operating current density. The developed model will serve as a tool for other researchers to enhance the electrochemical performance of aluminum sulfur batteries.