Inducing multiple polarizations in core@double-shell structured MXene/PVDF flexible nanodielectrics toward elevated overall dielectric performances

Titanium carbide (MXene) has garnered much attention in the development of high-permittivity (ε) flexible polymeric dielectrics because of its exceptionally high electrical conductivity; nevertheless, large dielectric loss at the percolating filler loading severely restricts their engineering applications. In this work, the exfoliated MXene was first surface-oxidized (O-MXene) and then encapsulated with a polydopamine (PDA) layer, and the dielectric properties of the O-MXene@PDA/polyvinylidene fluoride (PVDF) nanocomposites were investigated. The findings reveal that compared with both pristine MXene and MXene@PDA, the double-shell O-MXene@PDA imparts PVDF with evidently enhanced ε and breakdown strength (E_b) along with significantly lower dielectric loss. The elevated ε is ascribed to the O-MXene@PDA inducing multiple intra-particle and inter-particle polarizations. The presence of double shells not only induces deep charge traps capturing mobile charges but also raises the energy barrier for trapped charge de-trapping, subsequently leading to remarkably restrained loss and leakage current in the nanocomposites. Moreover, the second PDA interlayer enhances interfacial interactions between MXene and PVDF, and notably mitigates the strong dielectric mismatch between the two components, therefore lessening the formation of electric trees and promoting the E_b. The theoretical fitting and simulations provide deep insights into the underlying multiple polarization mechanisms and the impact of the double shells on charge migration. This core@double-shell approach offers new insights into the fabrication and design of percolating nanocomposites at low filler loading with concurrently high ε and E_b but low loss, presenting potential applications in power electronic devices and power systems.