Unique two-dimensional Prussian blue nanoplates for high-performance sodium-ion battery cathode

Prussian blue analogues (PBA) have been widely used as cathode materials in energy storage devices owing to their wide open-lattice frameworks, simple synthesis method, and high theoretical capacity. Generally, PBA synthesized via common precipitation between a chloride salt and a hexacyano complex are in a form of cubic particles (3D). Herein, nanoplates of PBA prepared via precipitation, without any template, are reported, and their superior electrochemical properties are evaluated. Instead of FeCl3, the precipitation used Fe(NO3)3 and K3Fe(CN)6 as feedstocks to produce nanoplates of Prussian green (2D PG), which can further react with NaI to form nanoplates of Prussian blue (2D PB). Morphologies and chemical compositions of the 2D PG depended on reaction temperatures. For example, 2D PG synthesized at 40 °C consisted of parallel plates in packs, whereas the one synthesized at 80 °C involved perpendicularly packed plates. Optimum electrochemical performances are obtained at a reaction temperature (2D PG's preparation) of 60 °C. A 2D-PB-based electrode combined with a polyacrylic acid (PAA)-polyaniline (PANI) (2:1) binder in a half-cell test with Na metal as a reference electrode exhibited high-rate properties (125 and 99 mAh g−1 at current densities of 10 and 500 mA g−1, respectively) and outstanding capacity retention (93% after 300 cycles). In a full-cell test with an [email protected] anode, the 2D-PB-based cathode delivered an initial specific capacity of 100 mAh g−1.