Polymer Dielectrics: Crystalline Materials as Energy Storage Systems

Dear Colleagues,

Over the past 30 years, use of polymer-based materials has changed the everyday life of the modern person due to their optimum light-weight, mechanical and thermal properties, and above all, their relatively cheap processability, compared to ceramics and metals. The aforementioned characteristics have shaped all household activities, the automobile and aeronautical industries, and the plastics industry worldwide to the worth of over $1 trillion as of 2016. In regards to their electrical properties, most polymers are dielectrics and thus are employed as electrical insulators to protect the conducting cables from environmental damage and safe use. However, when an electric field is applied upon a dielectric material, capacitive electrical energy can be stored due to polarization effects, a phenomenon that can be used in rechargeable energy storage devices. For such applications, a specific combination of properties is required, including (i) High values of dielectric permittivity, which is a measure of the ability of the material to store energy; (ii) low dielectric loss (tanδ) values, to maximize efficiency; (iii) low electrical conductivity, in order to reduce leakage currents; and (iv) high dielectric breakdown strength so higher electrical fields can be physically endured by the dielectric medium. These properties can be tailored from the addition of nanoinclusions of several shapes and electrical properties, to achieve the desired behaviour for each corresponding application.

The crystallinity and crystal morphology also affect the dielectric properties by enhancing interfacial polarization phenomena and increase the dielectric breakdown strength due to higher resistance to electrical treeing (current propagation to failure). The observed increase in breakdown strength is correlated with crystal orientation, as the crystallites provide higher potential barriers for electrical treeing. Towards this direction, biaxial orientation of semi-crystalline polymers, like polypropylene, have found use in thin dielectric membranes for film capacitors in electrical energy storage power system applications.

Dr. Aurora Nogales
Dr. Stavros Drakopoulos
Prof. Dr. Jan van Turnhout
Dr. Achilleas Pipertzis
Guest Editors

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• Energy materials
• Capacitive energy storage
• Dielectric materials
• Polymer nanodielectrics
• Broadband dielectric spectroscopy
• Interfacial polarization effects
• Charge transport
• Relaxation dynamics
• Insulator/conductor interface
• Crystalline polymers
• Charge/discharge efficiency