High‐Capacity Sodium–Prussian Blue Rechargeable Battery through Chelation‐Induced Nano‐Porosity

Abstract Across the different classes of sodium‐ion battery cathodes, Prussian Blue holds the greatest promise because of its high working potentials, abundance, low‐toxicity and ease of synthesis. However, its performance as a sodium‐ion battery cathode has generally been limited to less than 120 mAh g −1 , which is inferior compared to commercial lithium‐based counterparts. Here, sodium–Prussian Blue rechargeable batteries with a remarkably high discharge specific capacity of 153 ± 6 mAh g −1 at 1C is reported. This is achieved through the employment of excess ascorbic acid during the colloidal preparation of Prussian Blue crystals, followed by a 200 °C heat‐vacuum drying process. The optical, structural and thermogravimetric investigations show that the chelation of ascorbic acid to the iron ions disrupts the growth of Prussian Blue, and lead to the formation of a useful nano‐porous crystal structure. This allows for deeper percolation of sodium ions into the Prussian Blue crystals, and successfully unlocked useful inner volumes that are otherwise unreachable, thereby leading to an outstanding 47% elevation in specific capacity. This development brings sodium‐based battery technology significantly closer to the incumbent lithium‐ion batteries, and marks an important early step towards its practical application in commercial devices.