Co-Doped Electrochemically Exfoliated Graphene/Polymer Nanocomposites with High Dielectric Constant and Low Dielectric Loss for Flexible Dielectrics and Charge Storage

Electrochemically exfoliated graphene (EEG) with different levels of doping, electrical conductivity, and sheet size was synthesized with a one-step method and the resulting EEGs were incorporated in a poly(vinyl alcohol) (PVA) matrix via a simple solution-casting approach to prepare high-performance dielectrics. To maximize the EEG potential for making the nanocapacitor structure and minimizing the dielectric loss, we developed an aligned nanofiller structure. The aligned codoped EEG (as nanoelectrodes in the nanocapacitor structure, at 4.0 wt %) in the PVA matrix (as nanodielectric in the nanocapacitor structure) led to a high dielectric constant (203) and low dielectric loss (0.2) in X-band frequency. The chemical and structural characteristics of the nanocomposite account for the enhanced dielectric properties: (i) good dispersion of codoped EEG (nitrogen and sulfur doped) in the polymer matrix resulting in more effective nanocapacitors formation; (ii) enhanced polarization centers in the graphene due to nitrogen/sulfur doping, leading to a higher dielectric constant; (iii) aligned codoped EEG sheets, increasing the effective surface area of the nanocapacitor structure, enhancing the dielectric permittivity of the nanocomposite, and decreasing the dielectric loss; and (iv) functional groups at the surface of EEG acting as conduction barriers and decreasing the possibility of direct contacts of graphene sheets, reducing the dielectric loss.