Aqueous sulfur batteries: From electrode electrochemistry design to multivalent charge carrier strategy

Sulfur is an eco-friendly and low-cost material for high energy density batteries. Except for the widely reported sulfur electrochemistry in non-aqueous batteries, aqueous sulfur batteries have emerged as one of the most promising energy storage systems due to their high theoretical capacity and rapid redox kinetics. This work summarizes the research progress of aqueous sulfur batteries with multivalent charge carriers in the last decades, focusing on their electrodes, charge carriers and electrolytes with corresponding challenges, strategies, and applications. Briefly, we first delineate the forefront innovations of sulfur electrodes, spanning from the classification to their challenges and currently available strategies. Subsequently, we place special emphasis on the selection of charge carriers, including various reported cations such as Zn²⁺, Cu²⁺, Fe²⁺, Pb²⁺, Mn²⁺, Ca²⁺, Mg²⁺, Al³⁺, Co²⁺, Ni²⁺, Cd²⁺, and In³⁺. Considering the high reactivity of active metals in aqueous electrolytes, three strategies for electrode protection are summarized, including the employment of metal oxide electrodes, water-in-salt electrolytes, and hydrogel electrolytes. Finally, the practical electrochemical properties of different systems and their thermodynamics data are systematically compared to elaborate the feasibilities in particular application scenarios. This work aims to promote the development of aqueous sulfur batteries and provide guidance for their better design.