Sulfur-based aqueous batteries: electrochemistry and strategies

While research interest in aqueous batteries has surged due to their intrinsic low cost and high safety, the practical application is plagued by the restrictive capacity (less than 600 mAh g-1) of electrode materials. Sulfur-based aqueous batteries (SABs) feature high theoretical capacity (1672 mAh g-1), compatible potential, and affordable cost, arousing ever-increasing attention and intense efforts. Nonetheless, the underlying electrochemistry of SABs remains unclear, including complicated thermodynamic evolution and insufficient kinetics metrics. Consequently, multifarious irreversible reactions in various application systems imply the systematic complexity of SABs. Herein, rather than simply compiling recent progress, this Perspective aims to construct a theory-to-application methodology. Theoretically, attention has been paid to a critical appraisal of the aqueous-S-related electrochemistry, including fundamental properties evaluation, kinetics metrics with transient and steady-state analyses, and thermodynamic equilibrium and evolution. To put it into practice, current challenges and promising strategies are synergistically proposed. Practically, the above efforts are employed to evaluate and develop the device-scale applications, scilicet flow-SABs, oxide-SABs, and metal-SABs. Last, chemical and engineering insights are rendered collectively for the future development of high-energy SABs.