Covalently engineering novel sandwich-like rGO@POSS nanofillers for high-performance dielectric energy storage of PVDF film capacitor

With the development of modern electronic and electrical industry, it is still a great challenge to develop poly(vinylidene fluoride) (PVDF) based dielectric capacitors with high energy storage capability. Herein, a novel sandwich-like nanofiller was constructed via covalently grafting polyhedral oligomeric silsesquioxane onto graphene oxide nanosheets (GO@POSS), further PVDF/rGO@POSS film were fabricated via solvent-casting and in-situ thermal reduction processes. The results indicated that the grafting of POSS promoted the uniform dispersion of nanofillers to realize strong interfacial interaction with PVDF matrix. The optimal PVDF film containing 0.75 wt% rGO@POSS (0.75PGP-60) exhibited larger dielectric constant (ε_r = 13.32) and higher breakdown strength (E_b = 339.1 MV m⁻¹), thus resulting in synchronous improvements on energy density (U_e = 5.42 J·cm⁻³) and charge-discharge efficiency (η = 73.1 %), which increased by 95.0 % and 19.4 % compared to pure PVDF, respectively. Meanwhile, it presented excellent cycling stability with 97.6 % energy density retention after 10000^th cycles. The improved energy storage capability was attributed to reasonably-designed sandwich-like nanofiller: the formation of rGO micro-capacitors raised the dielectric constant of PVDF nanocomposites, while the insulative POSS layer helped to improve its breakdown strength and decrease its dielectric loss. The current work provides a novel and efficient paradigm to design PVDF nanocomposites with promising dielectric properties and energy storage capacity, and further contributes to broadening the practical applications of advanced dielectric capacitors.