Greatly improving energy storage density and reducing dielectric loss of carbon nanotube/cyanate ester composites through building a unique tri-layered structure with mica paper

Abstract

High dielectric loss and low energy storage density are common problems in available high dielectric constant composites consisting of a conductor and polymer. Herein, two unique kinds of tri-layered structure composites were designed and prepared. Specifically, 0.6 wt% of hydroxylated multi-walled carbon nanotubes (CNTs) were added into epoxy modified cyanate ester resin (CEP) to form a composite (CNT/CEP), which was used as the first and third layers of the tri-layered structure composite, respectively; the second layer is mica paper (MP) infiltrated with CNT/CEP or CEP resin. Consequently, the obtained tri-layered structure composite was coded as CNT/CEP–MPI–CNT/CEP or CNT/CEP–MPII–CNT/CEP. The influence of the thickness of MP and infiltration resin on the structure, dielectric properties and energy storage density of the tri-layered structure composite were investigated. The results show that with the same frequency and thickness of MP, the CNT/CEP–MPII–CNT/CEP composite has lower dielectric loss and larger energy storage density than CNT/CEP–MPI–CNT/CEP. More specifically, for the CNT/CEP–MPII–CNT/CEP composite in which the thickness of MP is 60 μm, the dielectric loss is only 0.07 at 100 Hz, about 7.6 × 10⁻⁵ times that of CNT/CEP; moreover, the energy storage density is 16.5 times that of CNT/CEP. This great increase in energy storage density and the simultaneous reduction in dielectric loss are the best values reported so far among composites based on a conductor/polymer layer and an insulating layer. The origin behind these attractive dielectric properties and energy storage densities of the tri-layered structure composites was discussed through simulating the equivalent circuit and correlating with structures.