Three different mechanisms of self-discharge behavior in poly(vinylidene fluoride-hexafluoropropylene) for dielectric energy storage

Abstract

Poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) has attracted attention as a matrix material for nanodielectrics, combining the high electrical breakdown of the polymer with the high permittivity of nanoparticles for improved energy storage properties. Although a large number of published works have reported increased discharged energy density for various nanocomposites, polarization and conduction loss mechanisms are rarely investigated. The latter are closely linked to the self-discharge behavior, which is crucial for future applications. This work aims to improve knowledge about loss and self-discharge mechanisms in doctor-blade-coated P(VDF-HFP) since its role in nanodielectrics is not fully understood. Combined analysis of cyclic unipolar electric displacement–electric field (D–E) characteristics and charging–lift–discharging measurements, where the measurement tip is lifted for a specific time between charging and discharging processes, reveals three Debye processes with different relaxation times: 20, 130 and 1340 s. The fast one correlates with the intrinsic conductivity of the polymer, which is dominated by space charge at high electric fields. The other two processes appear to saturate at an electric field of 100 MV m−1 so that their contribution to permittivity drops.