Supervisors: Prof. Enn Lust, Ph.D. Thomas Thomberg
Opponent: Prof. Thierry Brousse, Université de Nantes, Nantes, Prantsusmaa/France
Electrospinning is a well-known method for processing nanostructured scaffolds by applying a high electric field strength to a droplet of polymer solution. Due to the good flexibility, high porosity and easily influenced morphology, electrospun nanofiber membranes have very wide-ranging technological applications and it has been demonstrated that the electrospun nanofiber mats can be used as a separator material in the electrical double-layer capacitor (EDLC). EDLCs are energy storage devices with short charging and discharging times and high electrical efficiency, power density and very good cyclability. During last 10 years intensive research work has been done to improve the energy and power densities and cyclability of EDLC, designing the various porous electrode materials and electrolytes for applicable in EDLCs. However, little attention has been given to the role of the separator material and its influence on the electrochemical performance of EDLCs. The properties of the separator material used in EDLC are important as they give a significant contribution to the overall series resistance of a cell, as separator has effect on the ionic charge compensation rate between positively and negatively charged microporous carbon electrodes. Therefore the molar conductivity of ions in the porous separator matrix is extremely important. Influence of the separator characteristics (chemical composition, morphology, total porosity, specific surface area, pore size distribution) on the parameters of the electrical double-layer capacitor (EDLC) has been studied in the present work. It was found that the separator materials parameters have a noticeable influence on the specific power and characteristic time constant of the EDLC.