An aqueous BiI3-Zn battery with dual mechanisms of Zn2+ (de)intercalation and I−/I2 redox

The development of aqueous battery with dual mechanisms is now arousing more and more interest. The dual mechanisms of Zn²⁺ (de)intercalation and I⁻/I₂ redox bring unexpected effects. Herein, differing from previous studies using ZnI₂ additive, this work designs an aqueous BiI₃-Zn battery with self-supplied I⁻. Ex situ tests reveal the conversion of BiI₃ into Bi (discharge) and BiOI (charge) at the 1st cycle and the dissolved I⁻ in electrolyte. The active I⁻ species enhances the specific capacity and discharge medium voltage of electrode as well as improves the generation of Zn dendrite and by-product. Furthermore, the porous hard carbon is introduced to enhance the electronic/ionic conductivity and adsorb iodine species, proven by experimental and theoretical studies. Accordingly, the well-designed BiI₃-Zn battery delivers a high reversible capacity of 182 mA h g⁻¹ at 0.2 A g⁻¹, an excellent rate capability with 88 mA h g⁻¹ at 10 A g⁻¹, and an impressive cyclability with 63% capacity retention over 20 K cycles at 10 A g⁻¹. An excellent electrochemical performance is obtained even at a high mass loading of 6 mg cm⁻². Moreover, a flexible quasi-solid-state BiI₃-Zn battery exhibits satisfactory battery performances. This work provides a new idea for designing high-performance aqueous battery with dual mechanisms.