Boosting the sodium storage capability of Prussian blue nanocubes by overlaying PEDOT:PSS layer

Prussian blue and its analogues that have three-dimensional open frameworks are promising cathode materials for sodium-ion batteries owing to their high theoretical capacity and low production cost. Unfortunately, these materials are electrically insulating, which results in adverse effects on their electrochemical performance, such as limited practical capacity and rate capability. In this study, we demonstrate a simple overlaying of a conductive polymer— poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate)—on the surface of Prussian blue nanocubes at room temperature, with the aim to secure sufficient electrical conduction pathways and, by extension, improve the electrochemical performance of the nanocubes. The proposed surface-engineered Prussian blue nanocubes with 3.0 wt% poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) show a high reversible capacity (130.9 mA g⁻¹) with stable cycle performance. Moreover, they exhibit a reversible capacity of approximately 112.6 mAh g⁻¹ at the high rate of 1220 mA g⁻¹, which corresponds to 86.0% of the capacity obtained at a current density of 12.2 mA g⁻¹. Such improvements are mainly attributed to the formation of additional networks of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) that facilitate electric conduction in the electrode. Our proposed approach could be a practical solution to improving the electrochemical properties of Prussian blue and its analogues as potential cathode materials for high-performance sodium-ion batteries.