On 26 August at 14:15 Meelis Härmas will defend his thesis „Impact of activated carbon microstructure and porosity on electrochemical performance of electrical double-layer capacitors” for obtaining the degree of Doctor of Philosophy (Chemistry).
Thomas Thomberg (PhD), University of Tartu, Institute of Chemistry
Alar Jänes (PhD), University of Tartu, Institute of Chemistry
Associated Professor Olivier Crosnier, University of Nantes’i, France
Since the conventional power plants (wind, solar, hydro, nuclear, etc) currently do not fit in the pocket there is still an ever-increasing problem of needing newer and better energy storage devices. A part of the solution seems to come in the form of a device called supercapacitor. At first approximation, any energy storage system can be described by two main key parameters: energy and power. An electric car with a high energy battery system means it can drive further without needing to refill. If the same system had high power, then the car's acceleration from would be fast. That said, at equal basis, supercapacitors are considered to be cheap for obtaining high power values (<1 EUR kW−1) but costly in terms of energy storage (>4500 EUR (kWh)−1). Thus supercapacitors are used in applications that require high power intakes and outputs. For example, a smartphone camera uses supercapacitors for the flash.
One of the most influential supercapacitor components is electrodes. Most commonly the electrodes are made of carbon materials that are in nature similar to the carbon materials used in charcoal tablet and carbon materials in water filters. They all function because of a high active surface area. In the current study, several promising high surface area carbon materials were synthesised using glucose, saccharose and peat as precursors. Resulting materials were meticulously evaluated in a supercapacitor test cell and interpreted using modern structural analysis methods. Obtained results revealed that some synthesised materials consisted of 1 m (about 100 times smaller than the diameter of a human hair) spherical particles. Inside of these extremely small particles lays a complex porous network where a lot of additional surfaces is located (>2000 m2 g−1). These pores are accessible to small particles like ions and molecules that can find a home at pores. However, not all pores are equally good. Data indicated that the best pores for making high power supercapacitors were approximately 1 nm in diameter or wider (close to the diameter of a DNA molecule).