Protein Interfacial Gelation toward Shuttle-Free and Dendrite-Free Zn-Iodine Batteries

Aqueous zinc-iodine (Zn-I₂) batteries hold potential for large-scale energy storage but struggle with shuttle effects of I₂ cathodes and poor reversibility of Zn anodes. Here, an interfacial gelation strategy is proposed to suppress the shuttle effects and improve the Zn reversibility simultaneously by introducing silk protein (SP) additive. The SP can migrate bidirectionally toward cathode and anode interfaces driven by the periodically switched electric field direction during charging/discharging. For I₂ cathodes, the interaction between SP and polyiodides forms gelatinous precipitate to avoid the polyiodide dissolution, evidenced by excellent electrochemical performance, including high specific capacity and Coulombic efficiency (CE) (215 mAh g^-1 and 99.5% at 1 C), excellent rate performance (≈170 mAh g^-1 at 50 C), and extended durability (6000 cycles at 10 C). For Zn anodes, gelatinous SP serves as protective layer to boost the Zn reversibility (99.7% average CE at 2 mA cm^-2) and suppress dendrites. Consequently, a 500 mAh Zn-I₂ pouch cell with high-loading cathode (37.5 mg_iodine cm^-2) and high-utilization Zn anode (20%) achieves remarkable energy density (80 Wh kg^-1) and long-term durability (>1000 cycles). These findings underscore the simultaneous modulation of both cathode and anode and demonstrate the potential for practical applications of Zn-I₂ batteries.