Investigating the Impact of Copper and Zinc Doping in High‐Entropy Prussian Blue Analogues for Na‐Ion Batteries: From Material Analysis to Device Fabrication

High‐entropy Prussian blue analogues (HE‐PBAs) show great promise as active materials in Na‐ion batteries, particularly due to their multimetallic synergism that enhances electrochemical performance. This study explores two HE‐PBAs: Na 2 Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 Fe(CN) 6 (HE‐PBA‐1) and Na 2 Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 Zn 0.2 Fe(CN) 6 (HE‐PBA‐2). Both crystallize in monoclinic ( P 2 1 /n ) symmetry, but HE‐PBA‐1, with Cu, exhibits a lower bandgap, lower Na‐ion diffusion barrier, higher [Fe(CN) 6 ] vacancy, and smaller particle size compared to HE‐PBA‐2 with Zn. These factors result in higher power capability for HE‐PBA‐1 due to its enhanced electronic conductivity and Na‐ion diffusivity. Additionally, its higher [Fe(CN) 6 ] vacancy and smaller particle size offer more electrochemical active sites, improving energy characteristics. A Na‐ion full cell with HE‐PBA‐1 as the positive electrode and a mixed‐metallic sodium–copper–iron oxide (NaCuFe‐Oxide) as the negative electrode in a hydrogel electrolyte is assembled. It achieves a specific capacity of 94 mAh g −1 at 100 mA g −1 , an energy density of 70 Wh kg −1 at 74 W kg −1 , a power density of 375 W kg −1 at 57 Wh kg −1 , and excellent durability with 89% capacity retention over 500 cycles at 200 mA g −1 within a 0–2 V window. A 5 V/3 mAh prototype device is tested with a solar charging module to evaluate its real‐life feasibility.