Significantly enhanced energy density of nanodiamond/polyimide composites at high temperatures with ultralow nanodiamond contents

The development of miniature devices has generated a large demand for dielectric polymers with high energy storage density, especially at high temperatures. First, poly(methyl methacrylate) (PMMA)-coated nanodiamond (ND) particles were incorporated into a polyimide (PI) substrate to fabricate ND-g-PMMA/PI (NPP) composites. We found for the first time that with a very low content (0.4 vol.%) of ND particles, NPP-0.4 composite material gave the dielectric constant of 4.4, which is 37.5% higher than that of the PI film. The maximum energy density of the NPP-0.4 composite film achieves 9.4 J cm −3 at room temperature, which is 54% higher than that of the PI film. Furthermore, we found that the NPP-0.2 composite reaches the highest energy density and discharge efficiency of 5.77 J cm −3 and 72.3% at 150°C, which are 104% and 51.3% higher than those of the PI film at 150°C. This result shows a much higher energy density than most previously published results for high-temperature polymer capacitors. This phenomenon can be explained by the simulation results using COMSOL in which the interface polarization of ND/PI composites reached their maximum value with ultralow ND contents (0.4 vol.%). This research shows great promise for polymer capacitors with relatively high energy density at high temperatures.