In this work, pyromellitic dianhydride-based polyimide was hydrothermally synthesised and further thermally treated to prepare porous carbon materials. The porous structure of the polyimide-derived carbon can be controlled by varying the reactant concentrations during the hydrothermal reaction and KOH activation to achieve a highly accessible specific surface area of 1302 m2 g−1. A hybrid sodium-ion capacitor fabricated with the polyimide as anode and the polyimide-derived carbon as cathode can be operated at a voltage of 4.2 V, delivering an energy density of 66 Wh kg−1 at power density of 196 W kg−1, and an energy density of 13.3 Wh kg−1 at power density of 1200 W kg−1.