摘要： Capacitor films with high energy density are critical to energy storage. However, the energy density of state-of-the-art commercial capacitor films are limited by their low dielectric permittivity. In this study, epoxy-based nanocomposite films are prepared by filling with TiO2 nanofibers. Results show that nanocomposite films have larger discharge energy density because of the significant increase in dielectric permittivity, which caused by the additional interface polarization and space charge polarization. And a superior charge-discharge efficiency is achieved in the composite films at the same time due to the low dielectric loss. In addition, the composites also keep a high breakdown strength because of the dispersion of the nanofibers. The discharge energy density of 5.19 J/cm3 with the efficiency of 80% is achieved at 470 MV/m in the nanocomposites containing 2wt% nanofibers. The excellent energy density and charge-discharge efficiency of epoxy-based nanocomposites offer a promising opportunity for future researches and industrial application.