A Focused Review of Anthraquinone Derivatives for Aqueous Soft-Gel Electrode Batteries

Electrode design is crucial for achieving stable battery performance. Traditionally, electrode materials are categorized into solid- and liquid-state systems with distinct physical states. Between these two regimes exists a continuum of intermediate physical states, collectively referred to as soft-gel states, characterized by the absence of a rigid atomic framework and by restricted molecular mobility. By exploiting the strong water affinity of inorganic ions such as sulfate anions and the comparatively weak water affinity of certain water-soluble polymers, a distinct soft-gel phase can spontaneously form, providing a robust electrode-electrolyte interfacial architecture. Guided by the octanol-water partition coefficient (K_ow), this approach enables the construction of ion-exchange-membrane-free soft-gel electrode batteries with ultralong operational lifetimes. In this review, we highlight the modification strategies of anthraquinone derivatives in redox-flow batteries and discuss their potential integration into soft-gel hosts, thereby illustrating the feasibility of constructing soft-gel electrode batteries for durable aqueous energy storage.