Interface-modulated nanocomposites based on polypropylene for high-temperature energy storage

Polymer dielectrics with excellent energy storage properties at elevated temperatures are highly desirable in the development of advanced electrostatic capacitors for harsh environment applications. However, the state-of-the-art commercial capacitor dielectric biaxially oriented polypropylene (BOPP) has limited temperature capability below 105 ​°C. Here we report the interface modulation of a polypropylene (PP)-based nanocomposite that leads to substantially improved capacitive performance at elevated temperatures. The embedded nanoparticles are functionalized with a layer of polypropylene-graft-maleic anhydride (PP-g-mah) that is well miscible with the PP matrix. The PP-g-mah moieties not only contribute to the suppression of electrical conduction at high temperature by offering deep energy traps, but also benefit the improvement in dielectric constant due to the polar molecular element, which are proved by both the experimental results and computational simulation. The local deep traps introduced by the modulated interface are directly detected and quantitatively probed by the in-situ characterization using Kelvin probe force microscopy, further validating the rationale of the present approach. The resultant polymer nanocomposites display a discharged energy density of 1.66 ​J/cm3 and a charge-discharge efficiency of >90% at 400 ​MV/m and 120 ​°C, 615% that of the pristine PP film at the same conditions. The reported nanocomposites by interface modulation can be used to reduce the volume and weight of the capacitors and to eliminate the auxiliary cooling systems applied in the harsh environment.