Aqueous zinc‐ion batteries are receiving increasing attention; however, the development of high‐voltage cathodes is limited by the narrow voltage window of conventional aqueous electrolytes. Herein, it is reported that Na3V2(PO4)2O1.6F1.4 exhibits the excellent performance, optimal to date, among polyanion cathode materials in a novel neutral water‐in‐bisalts electrolyte of 25 m ZnCl2 + 5 m NH4Cl. It delivers a reversible capacity of 155 mAh g−1 at 50 mA g−1, a high average operating potential of ≈1.46 V, and stable cyclability of 7000 cycles at 2 A g−1.

Anion storage in cathode of dual-ion batteries provides leeway for new battery chemistries. For high energy density and better safety, it is desirable but challenging to reversibly intercalate chloride in a graphite cathode because either the oxygen or chlorine evolution reaction can prevail over chloride insertion. The primary barrier is the lack of suitable aqueous electrolytes that suppress these parasitic reactions. Herein, we report an aqueous deep eutectic solvent gel electrolyte that allows reversible chloride storage for graphite based on a chloride-based electrolyte via the formation of iodine–chloride interhalogens. The results suggest three reversible steps: iodine plating on the host surface, oxidation to form I-Cl interhalides, and then intercalation into graphite. As a result, the graphite cathode delivers a high reversible capacity of 291 mAh g–1 with stable cycling performance. Facilitated by the same mechanism, a porous graphenic carbon delivered a record-high capacity of over 1100 mAh g–1.

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Conventional cathodes generally store charges inside solids, and they usually suffer from compromised performance at low temperatures due to the energy barriers for ion transport. Here we report a reversible “plating” reaction of Cl2 liquid inside nanoporous carbon as a new electrode for low-temperature aqueous batteries. In a 7 m LiCl aqueous electrolyte, the activated carbon electrode delivers a high discharge capacity of 475 mAh/g (based on the carbon active mass in the working electrode) at 100 mA/g at −78 °C with a discharging plateau at ca. 0.95 V vs Ag/AgCl and retains a high capacity of 238 mAh/g at a high current rate of 1 A/g. Furthermore, this electrode system demonstrates stable cycling with ca. 65% capacity retention after 100 cycles at 500 mA/g with an average Coulombic efficiency of above 99%. The results provide a new option for high-energy halogen cathodes at low temperatures.