Foivos Markoulidis

Activated carbon from phenolic resin with controlled mesoporosity for an electric double-layer capacitor (EDLC)

Activated carbon materials are prepared from phenolic resin precursors by physical activation to fabricate electrodes for electric double-layer capacitors (EDLCs). Pore size and surface area of the carbon materials are controlled during the synthesizing process and after the carbonization through activation in a CO2 atmosphere to different levels of burn-off. The resultant carbon materials were evaluated as EDLC electrodes, using electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge (GCD) measurements with the organic electrolyte of spiro-(1,1′)-bipyrrolidinium tetrafluoroborate in propylene carbonate, SBPBF4/PC. The results of the study showed that the capacitance of carbon materials, as well as energy density of the EDLC cells, increased by increasing the level of burn-off (activation). The 46% activated carbon gave a capacitance of ∼160 F g−1 and an energy density of ∼35 W h kg−1, at a current density of 1 mA cm−2. The long term cycling tests showed high cycling stability of these carbon materials.

High-performance Supercapacitor cells with Activated Carbon/MWNT nanocomposite electrodes

The purpose of this work was to investigate and improve the performance of supercapacitor cells with carbon-based nanocomposite electrodes. The electrode structure comprised activated carbon (AC), four types of multi-wall nanotubes (MWNTs) and two alternative polymer binders, Polyvinyl alcohol (PVA) or Polyvinylidene fluoride (PVDF). Electrode fabrication involved various stages of mixing and dispersion of the AC powder and carbon nanotubes, rolling and coating of the AC/MWNT/binder paste on an aluminium substrate which also served as current collector. The organic electrolyte utilised was 1M tetraethylammonium tetrafluoroborate (TEABF4) fully dissolved in propylene carbonate (PC). All devices were of the electrochemical double layer capacitor (EDLC) type, incorporating four layers of tissue paper as separator material. The surface topography of the so fabricated electrodes was investigated with scanning electrode microscopy (SEM). Overall cell performance was evaluated with a multi-channel potentiostat/galvanostat/impedance analyser. Each supercapacitor cell was subjected to Cyclic Voltammetry (CV) at various scan rates from 0.01 V/s to 1 V/s, Charge-Discharge at a fixed current steps (2 mA) and Electrochemical Impedance Spectroscopy (EIS) with frequency range from 10 mHz to 1 MHz. It was established that an AC-based supercapacitor with 0.15%w/w MWNT content and 30 μm roll-coated, nanocomposite electrodes provided superior energy and power and energy densities while the cells was immersed in the electrolyte; well above those generated by the AC-based EDLC cells.

Carbon-Based Fibrous EDLC Capacitors and Supercapacitors

This paper investigates electrochemical double-layer capacitors (EDLCs) including two alternative types of carbon-based fibrous electrodes, a carbon fibre woven fabric (CWF) and a multiwall carbon nanotube (CNT) electrode, as well as hybrid CWF-CNT electrodes. Two types of separator membranes were also considered. An organic gel electrolyte PEO-LiCIO4-EC-THF was used to maintain a high working voltage. The capacitor cells were tested in cyclic voltammetry, charge-discharge, and impedance tests. The best separator was a glass fibre-fine pore filter. The carbon woven fabric electrode and the corresponding supercapacitor exhibited superior performance per unit area, whereas the multiwall carbon nanotube electrode and corresponding supercapacitor demonstrated excellent specific properties. The hybrid CWF-CNT electrodes did not show a combined improved performance due to the lack of carbon nanotube penetration into the carbon fibre fabric.

Cost analysis of supercapacitor cell production

A life cycle costing (LCC) is to be performed complementary to the ongoing research on an enhanced supercapacitor pouch cell, in order to provide additional decision support on the best cell chemistry from the economic point of view. Due to the early stage of the project so far merely the production phase is considered. The detailed cost calculation method was chosen and complemented with a scale up using dimension analysis and analogy analysis, in order to be able to utilize this method since available data is either scarce or refers to laboratory scale. It was found that the researched cells are within the lower margin of costs reported in literature. Also the relative contribution of material and production costs as well as energy consumption was in the same range as stated in literature. Although these comparisons should be handled with care as they do not always refer to the exact same item. Further, we concluded that the developed approach provides a sound basis for a reproducible calculation of production costs for technologies at an early research stage.

Ecological assessment of nano-enabled supercapacitors for automotive applications

New materials on nano scale have the potential to overcome existing technical barriers and are one of the most promising key technologies to enable the decoupling of economic growth and resource consumption. Developing these innovative materials for industrial applications means facing a complex quality profile, which includes among others technical, economic, and ecological aspects. So far the two latter aspects are not sufficiently included in technology development, especially from a life cycle point of view. Supercapacitors are considered a promising option for electric energy storage in hybrid and full electric cars. In comparison with presently used lithium based electro chemical storage systems supercapacitors possess a high specific power, but a relatively low specific energy. Therefore, the goal of ongoing research is to develop a new generation of supercapacitors with high specific power and high specific energy. To reach this goal particularly nano materials are developed and tested on cell level. In the presented study the ecological implications (regarding known environmental effects) of carbon based nano materials are analysed using Life Cycle Assessment (LCA). Major attention is paid to efficiency gains of nano particle production due to scaling up of such processes from laboratory to industrial production scales. Furthermore, a developed approach will be displayed, how to assess the environmental impact of nano materials on an automotive system level over the whole life cycle.

Ecological Assessment of Nano Materials for the Production of Electrostatic/Electrochemical Energy Storage Systems

Electrochemical double layer capacitors, also known as supercapacitors are considered as a promising option for stationary or mobile electric energy storage. At present lithium ion and nickel metal hydride batteries are used for automotive applications. In comparison to this type of batteries supercapacitors possess a high specific power, but a relatively low specific energy. Therefore, the goal of ongoing research is to develop a new generation of supercapacitors with high specific power and high specific energy. To reach this development goal particularly nano materials are under investigation on cell level. In the presented study the ecological implications (regarding known environmental effects) of carbon based nano materials are analysed using Life Cycle Assessment (LCA). Major attention is paid to efficiency gains of nano material production due to scaling up of such processes from laboratory to industrial production scales. Furthermore, a developed approach will be displayed, how to assess the environmental impact of nano materials on an automotive system level over the whole life cycle.

Nanomaterials and nanocomposites for high energy/high power supercapacitors

This study includes nanomaterials and nanocomposites for the fabrication of supercapacitor cells aiming at both high power and high energy densities. Activated carbon powder, multi-wall carbon nanotubes and graphene are considered as electrode materials. Electrochemical double layer supercapacitor cells (EDLCs) have been fabricated and tested to a maximum voltage of 3 V, where TEABF4 solution has been used as the organic electrolyte. The supercapacitors are proposed for applications of personal electronics, EV and HEV, and displays, depending on their maximum frequency of operation.

AUTOSUPERCAP: Development of High Energy and High Power Density Supercapacitor Cells

The study focuses on the materials and small supercapacitor cells manufactured in the first period of AUTOSUPERCAP project. The supercapacitor cells presented in this paper are of the type of symmetrical, electrochemical double layer capacitor (EDLC) cells with organic electrolyte TEABF4 dissolved in propylene carbonate (PC) or acetonitrile (AN). Different active electrode materials have been investigated, including novel activated carbon, graphene and carbon nanotubes produced in this project, as well as combinations of these materials. Supercapacitor cells of 2–4 cm2 area were fabricated and tested in impedance spectroscopy, cyclic voltammetry and charge-discharge tests. Ragone plots of energy density against power density were constructed from the charge-discharge test data at different current densities. Furthermore, the results of a cost analysis are presented for the main types of supercapacitors investigated.