Toward High-Energy and Long-Cycle-Life Prussian Blue-Based Aqueous\nSodium-Ion Batteries

Aqueous\nsodium-ion batteries (ARSIBs) have attracted increasing\nattention due to their intrinsic safety, greenness, abundant reserves,\nand easy recovery. However, the limited electrochemically stable window\n(1.23 V based on thermodynamics) of the aqueous electrolyte restricts\nthe energy density of ARSIBs. Hence, the energy density and cycle\nlife of ARSIBs are unsatisfactory. Here, we find that suppressing\nthe hydrogen/oxygen evolution reaction on active cathode/anode materials\nis primary to enlarging the electrochemical stable window (ESW) to\nobtain a high energy density. As a proof of concept, a Na<sub>1.78</sub>MnFe(CN)<sub>6</sub>·2.3H<sub>2</sub>O-based full cell with\na high voltage of 2 V and a discharge capacity of 130 mAh g<sup>–1</sup> delivers a high energy density of 100 Wh kg<sup>–1</sup> as\nwell as longevity of up to 4000 times.