Influence of Ionic Coordination on the Cathode Reaction Mechanisms of Al/S Batteries

The lack of knowledge on electrochemical reaction pathways for Al/S batteries prevents the development of practical approaches to mitigate the irreversibility and poor cycling performances of this appealing secondary battery system, which is, in theory, scalable, inexpensive, and energy-dense. Different from the Li/S system, Al/S batteries use ionic liquids (ILs) as electrolytes. The choice of the IL, i.e., whether the IL is based on a conventional EMImCl-based electrolyteor in a deep eutectic mixture of aluminum chloride with urea (or any of its derivatives), strongly affects the electrochemical energy-storage performance of the cell. To shed some light on the Al/S battery chemistry, here, we present the computational electrochemistry research work to determine the most favorable reaction pathways and thermodynamically stable reaction intermediates. We also discuss the effect of the coordination of ionic species (originated from aluminum-containing deep eutectic electrolytes) with polysulfide intermediates, which lead to alterations in the reaction pathway and electrochemical behavior of the Al/S system. The spectroscopic signatures from various reaction intermediates are also reported and validated via comparison with experimental observations.