▎ 摘　　要

Developing high dielectric performance of polymer nanocomposites is still a long-standing issue to simultaneously inherit the high dielectric constant of nanofillers and maintain the high breakdown strength of polymer matrix. In the current study, a tri-layered nanocomposite film is fabricated by a simple and effective solution-casting and dip-coating method, where graphene oxide nanosheets (GONSs) were modified by insulating SiO2 layer (SiO2@GONSs) and polyvinylidene fluoride (PVDF)/SiO2@GONS nanocomposite inner layer was sandwiched by polycarbonate (PC) layers. The surface modification could minimize the local electric field concentration and block conductive path. Furthermore, the sandwich or tri-layered structure inhibited the relaxation and migration of space charge or impurity ions and suppressed the charge injection, thus achieving enhanced breakdown strength and discharged energy efficiency. As a result, the as-prepared tri-layered nanocomposite film exhibited a dielectric constant of 5.2 and a low dielectric loss (tan delta) of 0.013 at 1 kHz, and breakdown strength of 219 MV m(-1), which was significantly higher than single-layered nanocomposite films and its counterpart without SiO2 modification. The corresponding discharged energy density was 1.20 J cm(-3) with an excellent efficiency of 86.2% at 200 MV m(-1). More interestingly, the insulating SiO2 modification layer and PC outer layers could also effectively restrict the relaxation or migration of impurity ions at a high temperature of 120 degrees C, endowing excellent high-temperature dielectric performance to the as-prepared tri-layered nanocomposite film. The combination of surface modification and sandwich structure opens up an avenue to fabricate GONS-based dielectric nanocomposites with low dielectric loss, high breakdown strength, high efficiency and high temperature tolerance. [GRAPHICS]