Fig. 7: Energy storage performances of epoxy/BT sponge composites and conuterparts filled with other BT fillers.

a D–E loops at 10 Hz of epoxy/50% BT sponge composites at various electric fields. b D–E loops at 10 Hz of the neat epoxy and epoxy/BT sponge composites with various BT loadings. The inset of b is D–E loops at 10 Hz for epoxy/50% BT NWs and epoxy/50% BT NPs composites. c Electric displacement, d discharged energy density, and e charge–discharge efficiency of the epoxy and epoxy/BT sponge composites at various electric fields. f Comparison of enhancement of discharged energy density (U_d/U_m) at 100 kV cm⁻¹ of epoxy composites filled with the 50% of BT sponge, BT NWs, and BT NPs. The inset of f is the voltage (V_c) on the epoxy/50% BT sponge composite capacitor and discharged energy density (U_d) of the epoxy/50% BT sponge composite capacitor upon charged to 100 kV cm⁻¹ in the practical discharge curve test (the capacitance is ~2 μF; the load in series is 2 kΩ). Error bars are SEM.