A Metallic Element-Free Halide-Ion Battery Enabled by Dual-halide Regulation in a Hydrogel Electrolyte

Reducing the reliance on metal minerals in rechargeable batteries is an important step toward sustainable energy storage. Although aqueous halogen redox systems are attractive due to their high redox potentials and intrinsic safety, most reported configurations still depend on concentrated metal salt electrolytes and/or metal anodes, limiting their sustainability. Here, we develop a completely metallic element-free halide-ion aqueous battery composed of a reduced graphene oxide (rGO) cathode, a viologen-based organic anode (TF-Cl), and a dual-halide hydrogel electrolyte. Incorporation of bromide and chloride species with distinct quaternary ammonium cations into a xanthan gum matrix establishes a confined ionic environment that stabilizes reactive polyhalide intermediates and suppresses shuttle behavior. Bromide-chloride interactions further regulate chlorine redox pathways, enabling cooperative stepwise halogen reactions with improved reversibility. Mechanistic studies indicate stabilized polyhalide formation and intercalation at the rGO cathode, together with reversible chloride storage at nitrogen redox sites in TF-Cl. The assembled full battery exhibits a stable discharge plateau, good rate capability, and cycling stability over 2000 cycles, demonstrating competitive capacity and enhanced output voltage relative to representative aqueous systems with metal-free electrodes.