Ultrafast Rechargeable Aqueous Zinc-Ion Batteries Based on Stable Radical Chemistry

Aqueous zinc-ion batteries (ZIBs) are a promising candidate for fast-charging energy-storage systems due to its attractive ionic conductivity of water-based electrolyte, high theoretical energy density, and low cost. Current strategies toward high-rate ZIBs mainly focus on the improvement of ionic or electron conductivity within cathodes. However, enhancing intrinsic electrochemical reaction kinetics of active materials to achieve fast Zn²⁺ storage has been greatly omitted. Herein, for the first time, stable radical intermediate generation is demonstrated in a typical organic electrode material (methylene blue [MB]), which effectively decreases the reaction energy barrier and enhances the intrinsic kinetics of MB cathode, enabling ultrafast Zn²⁺ storage. Meanwhile, anionic co-intercalation essentially avoids MB molecules rearranging their configuration and sharing Zn²⁺ with adjacent functional groups, thus keeps the structure stable. As a result, Zn–MB batteries exhibit an excellent rate capability up to 500C and ultralong life of 20 000 cycles with a negligible 0.07% capacity decay per cycle at 100C, which is superior to that of most reported aqueous ZIBs batteries. This work provides a novel strategy of stable radical chemistry for ultrafast-charging aqueous ZIBs, which can be introduced to other appropriate organic materials and multivalent ion battery systems.