Chunhong Lei | University of Surrey (original) (raw)

Papers by Chunhong Lei

Journal of Physical Chemistry C, May 5, 2022

Green Chemistry

Cobalt and manganese were selectively leached from LiNMC using an oxalic acid : choline chloride ... more Cobalt and manganese were selectively leached from LiNMC using an oxalic acid : choline chloride deep eutectic solvent, resulting in a nickel-enriched solid residue.

Supplemental material, sj-pdf-1-pia-10.1177_0957650920930166 for Development and evaluation of a ... more Supplemental material, sj-pdf-1-pia-10.1177_0957650920930166 for Development and evaluation of a composite supercapacitor-based 12 V transient start–stop power system for vehicles: Modelling, design and fabrication scaling up by Chunhong Lei, Richard Fields, Peter Wilson, Constantina Lekakou, Negar Amini, Stephen Tennison, John Perry, Michele Gosso and Brunetto Martorana in Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy

Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2020

The study involves a bottom-up approach, from bottom cells to large supercapacitor pouch cells, e... more The study involves a bottom-up approach, from bottom cells to large supercapacitor pouch cells, encompassing the design, modelling and fabrication stages of the cells leading to a 12 V transient start–stop (TSS) power system for automotive applications. More specifically, the design of a large composite supercapacitor is presented, consisting of a high power density component and a high energy density component, hybridised at material level. The composition of the composite supercapacitor is optimised to be application-specific so that it satisfies a specified energy-to-maximum power ratio for the 12 V TSS system. The testing of the large composite supercapacitor pouch cells and the 12 V TSS system proves the validity of the bottom-up approach, validates the design and the proposed electric circuit model and its parameters, fitted according to experimental data of small laboratory cells and applied successfully to the large cells, and proves the high quality of the scaled-up fabrica...

Energy Technology, 2016

The methodology was tested successfully in application-specific composite supercapacitors of medi... more The methodology was tested successfully in application-specific composite supercapacitors of medium and large size, fabricated in this study in the form of pouch cell with organic electrolyte. The application-specific composite supercapacitors offered a weight reduction of 40-60% compared to same performance supercapacitors based on the high power or on the high energy-related electrode material only.

Journal of Applied Electrochemistry, 2015

Phenolic resin-derived activated carbon (AC) cloths are used as electrodes for large-scale electr... more Phenolic resin-derived activated carbon (AC) cloths are used as electrodes for large-scale electric doublelayer capacitors or supercapacitors. To increase the energy and power density of the supercapacitor, the contact resistance between the carbon cloth and the aluminium foil current collector is reduced by modifying the Al current collectors. Different modified Al current collectors, including Toyal-Carbo Ò (surface-modified Al), DAG Ò (deflocculated Acheson TM graphite) coating and poly(3,4-ethylenedioxythiophene) (PEDOT) coating, have been tested and compared. The use of modified Al current collectors are shown to greatly reduce the contact resistance between the AC cloth and the Al foil. Another solution investigated in this study is to coat AC cloth with graphene through electrophoretic deposition (EPD). The graphene coated AC cloth is shown increased the capacitance and greatly reduced internal resistance.

Supercapacitors are essential in electric vehicles for supplying power during acceleration and re... more Supercapacitors are essential in electric vehicles for supplying power during acceleration and recovering braking energy. High power and sufficient energy density are required for both an effective power system but also to reduce weight. Supercapacitors of the symmetric, electrochemical double layer capacitor (EDLC) type are presented for automotive, grid, electrical, electronic and optoelectronic applications. The emphasis in our research is to increase not only power density but also energy density for these supercapacitors. Two types of porous electrode materials have been investigated: activated carbon (AC) fabrics and coatings.

Lecture Notes in Mobility, 2014

ABSTRACT The study focuses on the materials and small supercapacitor cells manufactured in the fi... more ABSTRACT 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.

Journal of Materials Chemistry A, 2013

ABSTRACT Activated carbon materials are prepared from phenolic resin precursors by physical activ... more ABSTRACT 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.

IOP Conference Series: Materials Science and Engineering, 2012

ABSTRACT The purpose of this work was to investigate and improve the performance of supercapacito... more ABSTRACT 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.

Electrochimica Acta, 2013

ABSTRACT Carbonaceous materials are commonly used to fabricate electrodes for electric double-lay... more ABSTRACT 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.

Carbon, 2014

The performance of supercapacitor cells with activated carbon (AC) electrodes was improved by add... more 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 (TEABF 4) 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 lm 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 TEABF 4 /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.

Applied Physics A, 2012

High-performance supercapacitors with organic electrolyte 1 M TEABF 4 (tetraethyl ammonium tetraf... more 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 inplane 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.

Carbonaceous materials are commonly used to fabricate electrodes for electric double-layer capaci... more Carbonaceous materials are commonly used to fabricate electrodes for electric double-layer capacitors (EDLCs) or supercapacitors. The internal resistance of the carbon electrode comes from the carbon material itself, carbon particle-particle contact, and carbon-current collector contact. The high internal resistance of the carbon electrode can decrease capacitor energy and power performance, and reduce the lifetime of the capacitor. In this report, the sources of carbon based EDLC internal resistance were explored using electrochemical impedance spectroscopy (EIS). A generalized equivalent circuit model was coupled with the EIS 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 the current collector, amount of polymer binder Poly(vinylidene fluoride) (PVDF) and carbon particle sizes on the internal resistance of the electrode.

Green Chemistry

Electric vehicle battery electrodes are delaminated ultra-fast using high-powered ultrasound, sep... more Electric vehicle battery electrodes are delaminated ultra-fast using high-powered ultrasound, separating active materials from the foil current collectors.

Surface and Coatings Technology

Nanoscale properties of conjugated polymers by Scanning Probe Microscopy Atomic force microscopy ... more Nanoscale properties of conjugated polymers by Scanning Probe Microscopy Atomic force microscopy (AFM) and electrostatic force microscopy (EFM) are explored and developed to study the surface potential distribution for a range of applications, including semiconductor laser devices, the electrical conductivity of aligned DNA molecules. The main focus of the thesis is the application of these techniques to investigate the nanoscale structures and electrical properties of conjugated polymers, including poly-(3-exylthiophene)s (P3ATs), polyfluorene (PFO), and poly-(3,4,-ethylenedioxythiophene) (PEDOT). EFM is a SPM technique, used to measure electrostatic force in non-contact mode. Two modes of EFM, scanning Kelvin probe microscopy (KPM or SKPM) and EFM/phase, are explored. Analytical calculations of tip-surface capacitances and their gradients are presented, aiming at quantifying the measurement. Based on the calculation results, the origin of the measurement resolution in EFM/phase and SKPM is explained, and a procedure is developed to convert the phase shift to the local surface potential. Thus, EFM/phase can also be used to measure the surface potential with higher resolution than SKPM. The self-assembled/aggregation structures of the polymers, as varied by molecular weight, solution preparation and substrates used, are investigated by AFM. The self assembled structure, usually in the form of a network, obeys certain laws in its formation. The surface potential distributions and charge transport properties in polymer films and network structures are investigated with both EFM modes. The electrical properties of Au on poly-(3-hexylthiophene) (P3HT) and P3HT on Au contacts are investigated. The electrochemical reaction of conjugated polymers, and electropolymerisation of 3,4-ethylenedioxythiophene (EDOT) are carried out on micro electrodes, and studied by AFM. The EDOT electropolymerization is shown to grow polymer nano-wires or a uniform polymer film, depending on conditions the electropolymerization process.

Journal of Physical Chemistry C, May 5, 2022

Green Chemistry

Cobalt and manganese were selectively leached from LiNMC using an oxalic acid : choline chloride ... more Cobalt and manganese were selectively leached from LiNMC using an oxalic acid : choline chloride deep eutectic solvent, resulting in a nickel-enriched solid residue.

Supplemental material, sj-pdf-1-pia-10.1177_0957650920930166 for Development and evaluation of a ... more Supplemental material, sj-pdf-1-pia-10.1177_0957650920930166 for Development and evaluation of a composite supercapacitor-based 12 V transient start–stop power system for vehicles: Modelling, design and fabrication scaling up by Chunhong Lei, Richard Fields, Peter Wilson, Constantina Lekakou, Negar Amini, Stephen Tennison, John Perry, Michele Gosso and Brunetto Martorana in Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy

Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2020

The study involves a bottom-up approach, from bottom cells to large supercapacitor pouch cells, e... more The study involves a bottom-up approach, from bottom cells to large supercapacitor pouch cells, encompassing the design, modelling and fabrication stages of the cells leading to a 12 V transient start–stop (TSS) power system for automotive applications. More specifically, the design of a large composite supercapacitor is presented, consisting of a high power density component and a high energy density component, hybridised at material level. The composition of the composite supercapacitor is optimised to be application-specific so that it satisfies a specified energy-to-maximum power ratio for the 12 V TSS system. The testing of the large composite supercapacitor pouch cells and the 12 V TSS system proves the validity of the bottom-up approach, validates the design and the proposed electric circuit model and its parameters, fitted according to experimental data of small laboratory cells and applied successfully to the large cells, and proves the high quality of the scaled-up fabrica...

Energy Technology, 2016

The methodology was tested successfully in application-specific composite supercapacitors of medi... more The methodology was tested successfully in application-specific composite supercapacitors of medium and large size, fabricated in this study in the form of pouch cell with organic electrolyte. The application-specific composite supercapacitors offered a weight reduction of 40-60% compared to same performance supercapacitors based on the high power or on the high energy-related electrode material only.

Journal of Applied Electrochemistry, 2015

Phenolic resin-derived activated carbon (AC) cloths are used as electrodes for large-scale electr... more Phenolic resin-derived activated carbon (AC) cloths are used as electrodes for large-scale electric doublelayer capacitors or supercapacitors. To increase the energy and power density of the supercapacitor, the contact resistance between the carbon cloth and the aluminium foil current collector is reduced by modifying the Al current collectors. Different modified Al current collectors, including Toyal-Carbo Ò (surface-modified Al), DAG Ò (deflocculated Acheson TM graphite) coating and poly(3,4-ethylenedioxythiophene) (PEDOT) coating, have been tested and compared. The use of modified Al current collectors are shown to greatly reduce the contact resistance between the AC cloth and the Al foil. Another solution investigated in this study is to coat AC cloth with graphene through electrophoretic deposition (EPD). The graphene coated AC cloth is shown increased the capacitance and greatly reduced internal resistance.

Supercapacitors are essential in electric vehicles for supplying power during acceleration and re... more Supercapacitors are essential in electric vehicles for supplying power during acceleration and recovering braking energy. High power and sufficient energy density are required for both an effective power system but also to reduce weight. Supercapacitors of the symmetric, electrochemical double layer capacitor (EDLC) type are presented for automotive, grid, electrical, electronic and optoelectronic applications. The emphasis in our research is to increase not only power density but also energy density for these supercapacitors. Two types of porous electrode materials have been investigated: activated carbon (AC) fabrics and coatings.

Lecture Notes in Mobility, 2014

ABSTRACT The study focuses on the materials and small supercapacitor cells manufactured in the fi... more ABSTRACT 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.

Journal of Materials Chemistry A, 2013

ABSTRACT Activated carbon materials are prepared from phenolic resin precursors by physical activ... more ABSTRACT 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.

IOP Conference Series: Materials Science and Engineering, 2012

ABSTRACT The purpose of this work was to investigate and improve the performance of supercapacito... more ABSTRACT 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.

Electrochimica Acta, 2013

ABSTRACT Carbonaceous materials are commonly used to fabricate electrodes for electric double-lay... more ABSTRACT 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.

Carbon, 2014

The performance of supercapacitor cells with activated carbon (AC) electrodes was improved by add... more 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 (TEABF 4) 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 lm 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 TEABF 4 /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.

Applied Physics A, 2012

High-performance supercapacitors with organic electrolyte 1 M TEABF 4 (tetraethyl ammonium tetraf... more 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 inplane 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.

Carbonaceous materials are commonly used to fabricate electrodes for electric double-layer capaci... more Carbonaceous materials are commonly used to fabricate electrodes for electric double-layer capacitors (EDLCs) or supercapacitors. The internal resistance of the carbon electrode comes from the carbon material itself, carbon particle-particle contact, and carbon-current collector contact. The high internal resistance of the carbon electrode can decrease capacitor energy and power performance, and reduce the lifetime of the capacitor. In this report, the sources of carbon based EDLC internal resistance were explored using electrochemical impedance spectroscopy (EIS). A generalized equivalent circuit model was coupled with the EIS 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 the current collector, amount of polymer binder Poly(vinylidene fluoride) (PVDF) and carbon particle sizes on the internal resistance of the electrode.

Green Chemistry

Electric vehicle battery electrodes are delaminated ultra-fast using high-powered ultrasound, sep... more Electric vehicle battery electrodes are delaminated ultra-fast using high-powered ultrasound, separating active materials from the foil current collectors.

Surface and Coatings Technology

Nanoscale properties of conjugated polymers by Scanning Probe Microscopy Atomic force microscopy ... more Nanoscale properties of conjugated polymers by Scanning Probe Microscopy Atomic force microscopy (AFM) and electrostatic force microscopy (EFM) are explored and developed to study the surface potential distribution for a range of applications, including semiconductor laser devices, the electrical conductivity of aligned DNA molecules. The main focus of the thesis is the application of these techniques to investigate the nanoscale structures and electrical properties of conjugated polymers, including poly-(3-exylthiophene)s (P3ATs), polyfluorene (PFO), and poly-(3,4,-ethylenedioxythiophene) (PEDOT). EFM is a SPM technique, used to measure electrostatic force in non-contact mode. Two modes of EFM, scanning Kelvin probe microscopy (KPM or SKPM) and EFM/phase, are explored. Analytical calculations of tip-surface capacitances and their gradients are presented, aiming at quantifying the measurement. Based on the calculation results, the origin of the measurement resolution in EFM/phase and SKPM is explained, and a procedure is developed to convert the phase shift to the local surface potential. Thus, EFM/phase can also be used to measure the surface potential with higher resolution than SKPM. The self-assembled/aggregation structures of the polymers, as varied by molecular weight, solution preparation and substrates used, are investigated by AFM. The self assembled structure, usually in the form of a network, obeys certain laws in its formation. The surface potential distributions and charge transport properties in polymer films and network structures are investigated with both EFM modes. The electrical properties of Au on poly-(3-hexylthiophene) (P3HT) and P3HT on Au contacts are investigated. The electrochemical reaction of conjugated polymers, and electropolymerisation of 3,4-ethylenedioxythiophene (EDOT) are carried out on micro electrodes, and studied by AFM. The EDOT electropolymerization is shown to grow polymer nano-wires or a uniform polymer film, depending on conditions the electropolymerization process.