A Study on the Reaction Mechanism of a Model Organic Cathode in Magnesium-Ion Batteries

The need for abundant, sustainable, and cost-effective energy storage technologies has been generating increased interests in batteries that rely on the use of earth abundant elements such as multivalent batteries. Those that utilize metallic anodes (Mg, Ca, Al) and organic cathodes are attractive as they can offer a path forward toward a competitive gravimetric energy density and in some cases fast charge capabilities. In particular, reports of a variety of Mg metal anode-organic cathodes batteries with good performances compel further research efforts of these systems and understanding of processes that govern their performances. However, studies of organic cathodes in competent, Cl- free Mg electrolytes remain limited, and the mechanisms that govern the cycling of these batteries are unclear. Herein, we assess the Mg battery performance using a typical benzoquinone type organic molecule in a competent Cl- free, single salt electrolyte and investigate the mechanisms at play. Combining the findings from battery and analytical studies reveal reversible structural transformations driven by a new precedence of a unique dissolution/precipitation mechanism. The implications of this mechanism on the performance of the battery are evaluated and discussed. The findings unveiled shed light onto potential challenges and opportunities with these systems and help guide future advancements.