A Rechargeable Aqueous Sodium‐Ion Battery

Abstract We report a rechargeable sodium‐ion battery in an aqueous environment with hydrophobic few‐layer graphene as the capacitive anode and hexacyanometallate as the insertion cathode. Owing to the lack of hydrophilic functionalities, sodium‐ion adsorption is selectively favored over H + adsorption at the hydrophobic anode/electrolyte interface without the complexity of widely encountered hydrogen‐ion insertion/H 2 evolution. Hydrophobicity precludes chemical bond formation with sodium ions, thereby improving reversibility and extended cyclability during charge discharge chemistry.