A High-Voltage and Cycle Stable Aqueous Rechargeable Na-Ion Battery Based on Na₂Zn₃[Fe(CN)₆]₂–NaTi₂(PO₄)₃ Intercalation Chemistry

Aqueous rechargeable Na-ion batteries (ARNBs) hold great promise for grid-scale electric energy storage because of their outstanding merits of low cost and resource abundance; however, their low energy density and poor cycling stability limit practical application. In this work, we reported a Prussian Blue (PB) analogue Na2Zn3[Fe(CN)6]2 as a high-voltage aqueous cathode for ARNBs and achieved its stable cycling at a high operation potential of 1.13 V (vs SHE) by using of a highly concentrated NaClO4 electrolyte. Raman spectroscopy, in situ XRD, and DFT calculations have been utilized to study the underlying mechanism of electrode performance as a function of electrolyte concentration. It was revealed that in the concentrated 17 m NaClO4 electrolyte almost all the water molecules are coordinated with Na+ ions, and the solvation energy of PB materials increases considerably with increasing salt concentrations, which broadens the electrochemical stability window of the electrolyte and greatly alleviates the dissolution of the materials. An aqueous rechargeable Na-ion battery was constructed by using a Na2Zn3[Fe(CN)6]2 cathode, a NaTi2(PO4)3 anode, and 17 m NaClO4 electrolyte. This full cell demonstrates a high-voltage output of 1.6 V and an energy density of 55 Wh kg–1 (based on the total mass of the electrode-active materials), offering a viable alternative to commercial aqueous batteries for large-scale EES applications.