Carrier Transport and Molecular Displacement Modulated dc Electrical Breakdown of Polypropylene Nanocomposites.

Daomin Min,Qingzhou Wu,Rui Mi,Zhaoliang Xing,Chenyu Yan,Yin Huang,Chao Ma,Shengtao Li

doi:10.3390/polym10111207

Daomin Min, Qingzhou Wu + Show 6 more

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https://doi.org/10.3390/polym10111207

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Abstract

Dielectric energy storage capacitors have advantages such as ultra-high power density, extremely fast charge and discharge speed, long service lifespan and are significant for pulsed power system, smart power grid, and power electronics. Polypropylene (PP) is one of the most widely used dielectric materials for dielectric energy storage capacitors. It is of interest to investigate how to improve its electrical breakdown strength by nanodoping and the influencing mechanism of nanodoping on the electrical breakdown properties of polymer nanocomposites. PP/Al2O3 nanocomposite dielectric materials with various weight fraction of nanoparticles are fabricated by melt-blending and hot-pressing methods. Thermally stimulated current, surface potential decay, and dc electrical breakdown experiments show that deep trap properties and associated molecular chain motion are changed by incorporating nanofillers into polymer matrix, resulting in the variations in conductivity and dc electrical breakdown field of nanocomposite dielectrics. Then, a charge transport and molecular displacement modulated electrical breakdown model is utilized to simulate the dc electrical breakdown behavior. It is found that isolated interfacial regions formed in nanocomposite dielectrics at relatively low loadings reduce the effective carrier mobility and strengthen the interaction between molecular chains, hindering the transport of charges and the displacement of molecular chains with occupied deep traps. Accordingly, the electrical breakdown strength is enhanced at relatively low loadings. Interfacial regions may overlap in nanocomposite dielectrics at relatively high loadings so that the effective carrier mobility decreases and the interaction between molecular chains may be weakened. Consequently, the molecular motion is accelerated by electric force, leading to the decrease in electrical breakdown strength. The experiments and simulations reveals that the influence of nanodoping on dc electrical breakdown properties may origin from the changes in the charge transport and molecular displacement characteristics caused by interfacial regions in nanocomposite dielectrics.

Highlights

With the continuous increase in energy consumption and the gradually deterioration of environment caused by using fossil energy, sustainable energy technology becomes more and more important for the energy transformation [1,2]
Experimental results measured by pulsed electro-acoustic (PEA) method indicated that under high electric fields homo space charges can accumulate in the bulk of PP dielectric material [9,19,20,23]
Since the displacement of a molecular chain with occupied deep traps would determine the electrical breakdown process, in the following numerical simulations we focus on the motion of molecular chains with deep traps

Summary

Introduction

With the continuous increase in energy consumption and the gradually deterioration of environment caused by using fossil energy, sustainable energy technology becomes more and more important for the energy transformation [1,2]. Dielectric energy storage capacitor has the advantages of ultra-high power density, extremely fast charge and discharge speed, environment friendly, long service lifespan, and low manufacturing cost [4], and has a great potential for the application in smart power grid, pulsed power system, and power electronics [4,5]. Capacitors store and release electric energy via polarization and depolarization of dielectric materials, which has no mass diffusion process. Since no chemical reactions involve in the storage and release of electric energy and dielectric materials such as polypropylene (PP), polyester, and polyimide maintain high electrical breakdown strength at relatively high temperatures, dielectric energy storage capacitor has long cycle life and can operate in high temperature circumstance [5,6,7]. It is necessary to develop dielectric materials with high electrical breakdown strength and high dielectric constant to enhance the energy density of dielectric energy storage capacitors [4,5]

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