Electrochemically Activated Highly Reversible Sulfate Conversion Enables High‐Voltage and Large‐Volumetric‐Capacity Zinc‐Based Anion–Cation Shuttle Battery

Aqueous dual‐ion batteries (DIBs) are becoming one of the most compelling choices for large‐scale stationary energy storage owing to the excellent safety performance, high power density, and cost‐effectiveness. However, their low output voltage leads to insufficient energy density. Here, we design a highly reversible pH‐neutral Ag↔Ag 2 SO 4 electrochemistry and construct a novel Zn‐based conversion‐type aqueous anion–cation shuttle DIB. A dendrite‐free Zn anode with functional graphite layer is prepared to improve cycle life. Benefitting from the synchronous effect of Zn 2+ /SO 4 2− dual charge carries and dendrite‐free anode, the DIB delivers a high output voltage of 1.41 V, volumetric energy density of 3295.4 Wh L −1 at 0.5 A g −1 , and 95.9% capacity retention over 300 cycles at 1 A g −1 , superior to most reported DIBs. As a proof of concept, we fabricate a quasi‐solid‐state aqueous DIB with remarkable mechanical strength, flexibility, and impressive temperature resistance. With working temperature decreasing from 20 to −10°C, it shows only a very low‐capacity loss (8.4%) and negligible polarization change (0.05 V). This work overcomes the bottleneck of low output voltage in aqueous DIBs and offers a promising pathway for the development of future aqueous batteries with high energy density.