Constructing Sulfur‐Heterocyclic Aromatic Amine Polymer with Multiple‐Redox Active Sites for Long‐Lifespan and All‐Organic Aqueous Magnesium Ion Batteries

Abstract Organic polymer materials have attracted much attention in rechargeable aqueous magnesium ion batteries (AMIBs) due to their sustainability and structural designability. However, the ionic storage capability is hindered by their insufficient redox‐active sites, dissolvability in aqueous electrolytes, and short‐range conjugated structures, resulting in low energy density and poor cycling stability. Herein, a sulfur‐heterocyclic aromatic polyimide‐based organic polymer (PTDBS) is constructed with multiple redox‐active sites and long‐range conjugate, which is employed as active material for AMIB anode, achieving an outstanding Mg 2+ storage capability. Benefitting from the introduced thioether bonds, PTDBS possesses an enhanced electronic conductivity and additional redox‐active sites for reversible Mg 2+ coordination, thus ensuring high redox activity and superior electron affinity. As a result, the PTDBS electrode delivers ultrafast and stable Mg 2+ storage in an MgCl 2 aqueous electrolyte with a superior rate capacity of 98.6 mA h g −1 at 10.0 A g −1 , and remarkable cycling stability over 7500 cycles with a capacity retention rate of 90.0%. Notably, the all‐organic aqueous full cell, realized by coupling the PTDBS anode and the polyindole cathode, achieves a high energy density and long lifespan. This work lays the foundation for the development of highly stable all‐organic electrode materials for large‐scale aqueous energy storage.