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

Aqueous sodium-ion batteries (ARSIBs) have attracted increasing attention due to their intrinsic safety, greenness, abundant reserves, and easy recovery. However, the limited electrochemically stable window (1.23 V based on thermodynamics) of the aqueous electrolyte restricts the energy density of ARSIBs. Hence, the energy density and cycle life of ARSIBs are unsatisfactory. Here, we find that suppressing the hydrogen/oxygen evolution reaction on active cathode/anode materials is primary to enlarging the electrochemical stable window (ESW) to obtain a high energy density. As a proof of concept, a Na1.78MnFe(CN)6·2.3H2O-based full cell with a high voltage of 2 V and a discharge capacity of 130 mAh g–1 delivers a high energy density of 100 Wh kg–1 as well as longevity of up to 4000 times.