Significantly improved high-temperature energy storage performance of PP films by grafting-cross-linking modification

Abstract

Polypropylene (PP) film capacitors are widely utilized owing to their high breakdown strength and excellent processability. However, the dielectric loss of PP increases significantly at elevated temperatures, making it challenging to achieve both high energy density and high discharge efficiency simultaneously. This study introduces a novel strategy by incorporating cross-linking points to construct a three-dimensional network structure, which enhances the stability of the molecular architecture. By grafting acrylic acid (AA) to modulate the free volume, the polarization is strengthened while the relaxation loss is effectively suppressed. Additionally, deep traps are introduced to improve the carrier capture capability. This approach achieves an optimal balance between energy storage capacity and processability, thereby substantially enhancing the electrical performance of PP films. As a result, the Hg-XLPP film unit exhibits outstanding performance, including an ultrahigh energy density (8.9 J cm⁻³) and remarkable discharging efficiency (>84%) at 840 MV m⁻¹. This study proposes a novel strategy that effectively integrates cross-linking and grafting to optimize the molecular chain structure of PP. By modulating the free volume and introducing deep traps, the high-temperature energy storage capability of PP-based capacitor films is significantly enhanced.