Markoulidis F, Lei C, Lekakou C, Duff D, Khalil S, Martorana B, Cannavaro I (2014) A method to increase the energy density of supercapacitor cells by the addition of multiwall carbon nanotubes into activated carbon electrodes, Carbon 68 pp. 58-66
The performance of supercapacitor cells with activated carbon (AC) electrodes was improved by adding a small amount of multiwall carbon nanotubes (MWCNTs). The electrode structure investigated comprised AC, four different types of MWCNTs and two polymer binders, polyvinylidene fluoride or polyvinyl alcohol. All fabricated devices were of the electrochemical double layer capacitor type. The organic electrolyte used was tetraethyl ammonium tetrafluoroborate (TEABF4) in two different solvents: propylene carbonate or acetonitrile (AN). The electrodes were characterised with scanning electron microscopy and tested for their specific surface area and pore size distribution. The electrode fabrication process was fine-tuned by investigating the effect of the coating thickness on the supercapacitor cell performance. It was established that an AC/MWCNT-based supercapacitor with 30 ¼m thick roll-coated, composite electrodes of just 0.15%w/w MWCNT content provided superior tested power and energy densities of 38 kW/kg and 28 W h/kg, respectively, compared to 18 kW/kg and 17 W h/kg for AC only-based cells in a 1.5 TEABF4/AN electrolyte. The increased energy density was attributed to a fine lace of MWCNTs covering the AC microparticles with visible 20-30 nm lace pores and to the high specific area of micropores. © 2013 Elsevier Ltd. All rights reserved.
Dura H, Perry J, Lecacou T, Markoulidis F, Lei C, Khalil S, Decker M, Weil M (2013) Cost analysis of supercapacitor cell production, 4th International Conference on Clean Electrical Power: Renewable Energy Resources Impact, ICCEP 2013 pp. 516-523
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. © 2013 IEEE.
Lekakou C, Lei C, Markoulidis F, Sorniotti A (2012) Nanomaterials and Nanocomposites for High Energy/High Power Supercapacitors, 2012 12TH IEEE CONFERENCE ON NANOTECHNOLOGY (IEEE-NANO) IEEE
Lei C, Markoulidis F, Ashitaka Z, Lekakou C (2013) Reduction of porous carbon/Al contact resistance for an electric double-layer capacitor (EDLC), Electrochimica Acta 92 pp. 183-187
Carbonaceous materials are commonly used to fabricate electrodes for electric double-layer capacitors (EDLCs) or supercapacitors. The high contact resistance between the carbon active layer and the Al current collector can decrease capacitor energy and power performance, and shorten the lifetime of the capacitor. In this report, the sources of carbon based EDLC internal resistance were explored using electrochemical impedance spectroscopy (EIS). An equivalent circuit model was coupled with the EIS data for the analyses. The EDLC cells were made from symmetric carbon/Al electrodes and operated in organic electrolyte. The analysis results showed the effects of pressure and modified Al on the contact resistance, where a novel, carbon modified Al collector with Al4C3 nano whiskers greatly reduced the contact resistance. Finally the effect of scale-up on the internal resistance was discussed. © 2013 Elsevier Ltd.
Weil M, Dura H, Shimon B, Baumann M, Zimmermann B, Ziemann S, Lei C, Markoulidis F, Lekakou T, Decker M (2012) Ecological assessment of nano-enabled supercapacitors for automotive applications, IOP Conference Series: Materials Science and Engineering 40 (1)
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. © Published under licence by IOP Publishing Ltd.
Weil M, Dura H, Balint S, Baumann MJ, Zimmermann BM, Ziemann S, Lei C, Markoulidis F, Lekakou C, Decker M (2013) Ecological Assessment of Nano Materials for the Production of Electrostatic/Electrochemical Energy Storage Systems, In: Njuguna J (eds.), Structural Nanocomposites Springer Berlin Heidelberg
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.
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-LiCIO 4-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. © 2011 C. Lekakou et al.
Markoulidis F, Lei C, Lekakou C, Figgemeier E, Duff D, Khalil S, Martorana B, Cannavaro I (2012) High-performance Supercapacitor cells with Activated Carbon/MWNT nanocomposite electrodes, IOP Conf.Series:MaterialsScienceandEngineering 40 (2012) 012021 40 IOP Publishing
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 ¼m 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.
Vermisoglou E, Todorova N, Pilatos G, Romanos G, Likodimos V, Boukos N, Lei C, Markoulidis F, Lekakou C, Trapalis C (2012) Few layer graphenes decorated with silver nanoparticles, ECCM 2012 - Composites at Venice, Proceedings of the 15th European Conference on Composite Materials
Graphite oxide (GO) powder was irradiated in a microwave oven and lightweight expanded graphite oxide (EGO) powder with high BET surface area 1316 m2/g was obtained. Activation of EGO was performed by impregnation in KOH solution and high temperature treatment under Ar flow, followed by annealing in vacuum (t-EGO). KOH acted more as a reducing agent diminishing the defects than as a surface modifier for high porosity. EGO and t-EGO were further decorated with Ag nanoparticles (
Markoulidis F, Lei C, Lekakou C (2013) Fabrication of high-performance supercapacitors based on transversely oriented carbon nanotubes, Applied Physics A: Materials Science and Processing 111 (1) pp. 227-236
High-performance supercapacitors with organic electrolyte 1 M TEABF 4 (tetraethyl ammonium tetrafluoroborate) in PC (propylene carbonate) were fabricated and tested, based on multiwall carbon nanotubes (MWNTs) deposited by electrophoresis on three types of alternative substrates: aluminium foil, ITO (indium tin oxide) coated PET (polyethylene terephthalate) film and PET film. In all cases, SEM (scanning electron microscopy) and STEM (scanning transmission electron microscopy) micrographs demonstrated that protruding, transversely oriented MWNT structures were formed, which should increase the transverse conductivity of these MWNT electrodes. The best supercapacitor cell of MWNT electrodes deposited on aluminium foil displayed good transverse orientation of the MWNT structures as well as an in-plane MWNT network at the feet of the protruding structures, which ensured good in-plane conductivity. Capacitor cells with MWNT electrodes deposited either on ITO-coated PET film or on PET film demonstrated lower but still very good performance due to the high density of transversely oriented MWNT structures (good transverse conductivity) but some in-plane inhomogeneities. Capacitor cells with drop-printed MWNTs on aluminium foil, without any transverse orientation, had 16-30 times lower specific capacitance and 5-40 times lower power density than the capacitor cells with the electrophoretically deposited MWNT electrodes. © 2012 Springer-Verlag Berlin Heidelberg.
Lekakou C, Markoulidis F, Lei C, Sorniotti A, Perry J, Hoy C, Martorana B, Cannavaro I, Gosso M (2012) Meso-nano and micro-nano ion transport in porous carbon composite electrodes for energy storage applications, ECCM 2012 - Composites at Venice, Proceedings of the 15th European Conference on Composite Materials
In energy storage devices carbonaceous composite electrodes are a popular choice, consisting of activated carbon (ac), conductive additives and a polymeric binder matrix. The active electrode components are in the form of ac particles, ac fibres, or ac monolith combined with conductive additives such as carbon black. Activated carbon plays the most important role for storing a large amount of energy in the form of ions contained in the carbon nanopores. This study considers a modelling approach to the meso-nano and micro-nano infiltration of ions into the porous carbon structure during the operation of the energy storage device. Depending on the pore size, ion size and solvent molecule size, ions may be solvated or unsolvated as they move, where ions are solvated in meso-pores for most cases. Molecular model simulations have been performed to determine the values of the geometrical parameters of different ions, solvated and unsolvated in various solvents. A meso-nano and micro-nano ion infiltration model has been developed in this study under both steady state and dynamic conditions.
Lei C, Amini N, Markoulidis F, Wilson P, Tennison S, Lekakou C (2013) Activated carbon from phenolic resin with controlled mesoporosity for an electric double-layer capacitor (EDLC), Journal of Materials Chemistry A 1 (19) pp. 6037-6042
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-(1,12)-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
Composite materials in electrodes for energy storage devices can combine different
materials of high energy density, in terms of high specific surface area and pseudocapacitance, with
materials of high power density, in terms of high electrical conductivity and features lowering the
contact resistance between electrode and current collector. The present study investigates composite
coatings as electrodes for supercapacitors with organic electrolyte 1.5 M TEABF4 in acetonitrile. The
composite coatings contain high surface area activated carbon (AC) with only
0.15 wt% multiwall carbon nanotubes (MWCNTs) which, dispersed to their percolation limit, offer
high conductivity. The focus of the investigations is on the decoration of MWCNTs with silver
nanoparticles, where smaller Ag crystallites of 16.7 nm grew on carboxylic group-functionalized
MWCNTs, MWCNT?COOH, against 27?32 nm Ag crystallites grown on unfunctionalized
MWCNTs. All Ag-decorated MWCNTs eliminate the contact resistance between the composite
electrode and the current collector that exists when undecorated MWCNTs are used in the
composite electrodes. Ag-decorated MWCNT?COOH tripled the power density and Ag-decorated
MWCNT additive doubled the power density and increased the maximum energy density by 6%,
due to pseudocapacitance of Ag, compared to composite electrodes with undecorated MWCNTs.