This work reveals a three-stage mechanism of Na intercalation into one of the state-of-the-art battery electrode materials operating in aqueous electrolytes.

The so-called Prussian blue analogues (PBAs) are spotlighted as promising cathode materials for aqueous Na-ion batteries regarding their good performance for the application in future large-scale energy storage systems. In this work, we demonstrate that one of the PBA representatives, namely NaVO[Fe(CN)] thin films (VHCFs), is a promising cathode material for aqueous Na-ion batteries with very positive intercalation/deintercalation potentials, which might likely designate a new benchmark in the field. To maximize the material utilization, we have formed VHCF thin films on model current collectors from aqueous solutions. The resulting films demonstrated a very positive half-charge potential (ΔE ≈ 0.91 V vs Ag/AgCl reference electrode) in acidic media with a specific capacity of ∼80 mAh g recorded at high C-rates (30 C) in 1 M LiNO, 3 M NaNO and 3 M KNO electrolytes in the presence of 3.6 M HSO. It is also shown that well-known solvation effects related to the nature of the alkali metal cations during intercalation and deintercalation are surprisingly not pronounced in the case of VHCFs.

Intercalation of alkali metal cations, like Li+ or Na+, follows the same three‐stage mechanism of the interfacial charge and mass transfer irrespective of the nature of the electrolyte, electrolyte composition or electrode material.