An active bifunctional natural dye for stable all-solid-state organic batteries.

Sustainable and cost-effective organic electrode materials are promising for next-generation lithium-ion batteries but are hindered by severe shuttle effects. While all-solid-state batteries offer a potential solution, chemical and mechanical incompatibility between organic electrode materials and inorganic solid electrolytes limit areal capacity and cycling stability, falling short of practical requirements. Here, we report a bifunctional indigo natural dye that serves as both an active material and a solid molecular catalyst in sulfide-based all-solid-state batteries, addressing these compatibility challenges. Contrary to the prevailing view that chemical reactions between organic electrode materials and sulfide solid electrolytes are detrimental, our study reveals that controlled reactions between indigo and Li₆PS₅Cl solid electrolyte catalyze their synergistic redox process after optimizing electrode microstructures. This strategy enables a high reversible capacity of 583 mAh g^-1 (Li₆PS₅Cl contribution: 379 mAh g^-1) at 0.1 C, a high areal capacity of 3.84 mAh cm^-2, and good cycling stability at an operation temperature of 25 °C. These findings highlight the potential of bifunctional organic electrode materials in sulfide-based all-solid-state batteries to overcome the key challenges of organic electrode materials in practical applications.