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Low-Cost, Environmentally Friendly Electric Double-Layer Capacitors: Concept, Materials and Production
Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
2017 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Today’s society is currently performing an exit from fossilfuel energy sources. The change to sustainable alternativesrequires inexpensive and environmentally friendly energy storagedevices. However, most current devices contain expensive,rare or toxic materials. These materials must be replaced bylow-cost, abundant, nontoxic components.In this thesis, I suggest the production of paper-based electricdouble-layer capacitors (EDLCs) to meet the demand oflow-cost energy storage devices that provide high power density.To fulfill the requirements of sustainable and environmentallyfriendly devices, production of EDLCs that consist of paper,graphite and saltwater is proposed. Paper can be used as aseparator between the electrodes and as a substrate for theelectrodes. Graphite is suited for use as an active material in theelectrodes, and saltwater can be employed as an electrolyte.Westudied and developed different methods for the productionof nanographite and graphene from graphite. Composites containingthese materials and similar advanced carbon materialshave been tested as electrode materials in EDLCs. I suggest theuse of cellulose nanofibers (CNFs) or microfibrillated cellulose(MFC) as a binder in the electrodes. In addition to improvedmechanical stability, the nanocellulose improved the stabilityof graphite dispersions and the electrical performance of theelectrodes. The influence of the cellulose quality on the electricalproperties of the electrodes and EDLCs was investigated.The results showed that the finest nanocellulose quality is notthe best choice for EDLC electrodes; MFC is recommended forthis application instead. The results also demonstrated thatthe capacitance of EDLCs can be increased if the electrodemasses are adjusted according to the size of the electrolyte ions.Moreover, we investigated the issue of high contact resistancesat the interface between porous carbon electrodes and metalcurrent collectors. To reduce the contact resistance, graphitefoil can be used as a current collector instead of metal foils.Using the suggested low-cost materials, production methodsand conceptual improvements, it is possible to reduce the material costs by more than 90% in comparison with commercialunits. This confirms that paper-based EDLCs are apromising alternative to conventional EDLCs. Our findings andadditional research can be expected to substantially supportthe design and commercialization of sustainable EDLCs andother green energy technologies.

Abstract [sv]

I dagens samhälle pågår en omställning från användning avfossila energikällor till förnybara alternativ. Denna förändringkräver miljövänliga och kostnadseffektiva elektriska energilagringsenheterför att möjliggöra en kontinuerlig energileverans.Dagens energilagringsenheter innehåller ofta dyra, sällsyntaeller giftiga material som behöver bytas ut för att nå hållbaralösningar.I denna avhandling föreslås att tillverka pappersbaseradesuperkondensatorer som möter kraven för kostnadseffektivaelektriska energilagrare med hög effekttäthet. För att nå kravenpå miljömässigt hållbara enheter föreslås användning avendast papper, grafit och saltvatten. Papper kan användas somseparator mellan elektroder likväl som substrat vid elektrodbestrykning.Grafit kan användas som aktivt elektrodmaterialoch saltvatten fungerar som elektrolyt. Olika metoder har härutvecklats för att producera nanografit och grafen från grafit.Dessa material har tillsammans med liknande, kommersiellt tillgängliga,avancerade kolmaterial testats i elektrodkompositerför superkondensatorer. Som bindemedel i dessa kompositerföreslås nanofibrillerad eller mikrofibrillerad cellulosa. Jaghar demonstrerat att nanocellulosa ökar dispersionsstabilitetensamt förbättrar den mekaniska stabiliteten och dom elektriskaegenskaperna i elektroderna. Hur cellulosans kvalitet påverkarelektroderna har undersökts och visar att den finaste kvaliteteninte är det bästa valet för superkondensatorer, istället rekommenderasmikrofibrillerad cellulosa. Utöver detta demonstrerasmöjligheten att öka superkondensatorernas kapacitans genomatt balansera elektrodernas massa med hänsyn till jonernasstorlek i elektrolyten. I avhandlingen diskuteras även svårigheternamed hög kontaktresistans i gränssnittet mellan porösakolstrukturer och metallfolie och hur detta kan undvikas omgrafitfolie används som kontakt.Genom att använda de material, produktionstekniker ochkonceptförbättringar som föreslås i avhandlingen är det möjligtatt reducera materialkostnaderna med mer än 90% i jämförelsemed kommersiella superkondensatorer. Detta bekräftar att pappersbaserade superkondensatorer är ett lovande alternativoch våra resultat tillsammans med vidare utveckling harstor potential att stödja övergången till miljömässigt hållbarasuperkondensatorer och annan grön energiteknik.

Ort, förlag, år, upplaga, sidor
Sundsvall: Mid Sweden University , 2017. , s. 157
Serie
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 267
Nyckelord [en]
Electric Double-Layer Capacitor, Graphite, Cellulose Nanofibers, Large-Scale, Mass Balancing, Metal-Free
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
URN: urn:nbn:se:miun:diva-31539ISBN: 978-91-88527-23-3 (tryckt)OAI: oai:DiVA.org:miun-31539DiVA, id: diva2:1138271
Disputation
2017-09-08, M102, Holmgatan 10, Sundsvall, 10:15 (Engelska)
Handledare
Anmärkning

Vid tidpunkten för disputationen var följande delarbeten opublicerade: delarbete 6 inskickat.

At the time of the doctoral defence the following papers were unpublished: paper 6 submitted.

Tillgänglig från: 2017-09-07 Skapad: 2017-09-04 Senast uppdaterad: 2018-05-21Bibliografiskt granskad
Delarbeten
1. Supercapacitors with graphene coated paper electrodes
Öppna denna publikation i ny flik eller fönster >>Supercapacitors with graphene coated paper electrodes
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2012 (Engelska)Ingår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, nr 2, s. 481-485Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Paper based supercapacitors are prepared by stacking a paper between two graphene electrodes and soaking these in an aqueous electrolyte. We demonstrate that supercapacitors can easily be manufactured by using proven paper technologies. Several different electrode materials were compared and two types of contacting material, silver and graphite foil were tested. The influence of the paper used as separator was also investigated. The supercapacitors with a graphene-gold nanoparticle composite as electrodes showed a specific capacitance of up to 100 F/g and an energy density of 1.27 Wh/kg. The energy density can further be increased by using other electrolytes. The silver contacts showed a pseudo capacitance, which the graphite contacts did not. The papers tested had a minor effect on the capacitance, but they have an influence on the weight and the volume of the supercapacitor.

Nyckelord
Coating; Graphene; Graphite; Paper; Supercapacitor
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:miun:diva-16880 (URN)10.3183/NPPRJ-2012-27-02-p481-485 (DOI)000315696000044 ()2-s2.0-84865260056 (Scopus ID)STC (Lokalt ID)STC (Arkivnummer)STC (OAI)
Tillgänglig från: 2013-04-04 Skapad: 2012-08-29 Senast uppdaterad: 2017-12-07Bibliografiskt granskad
2. Enhanced electrical and mechanical properties of nanographite electrodes for supercapacitors by addition of nanofibrillated cellulose
Öppna denna publikation i ny flik eller fönster >>Enhanced electrical and mechanical properties of nanographite electrodes for supercapacitors by addition of nanofibrillated cellulose
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2014 (Engelska)Ingår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 251, nr 12, s. 2581-2586Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Graphene and porous carbon materials are widely used as electrodes in supercapacitors. In order to form mechanically stable electrodes, binders can be added to the conducting electrode material. However, most bindersdegrade the electrical performance of the electrodes. Here we show that by using nanofibrillated cellulose(NFC) as binder the electrical properties, such as capacitance, were enhanced. The highest capacitance was measured at a NFC content of approximately 10% in ratio to the total amount of active material. NFC is a good ionconductor and improves the access of ions in the electrodes. Thus, electrodes made of a mixture of nanographite and NFC achieved larger capacitances in supercapacitors than electrodes with nanographite only. In addition to electrical properties, NFC enhanced the mechanical stability and wet strength of the electrodes significantly. Furthermore, NFC stabilized the aqueous nanographite dispersions, which improved the processability. Galvanostatic cycling was performed and an initial transient behaviour of the supercapacitors during the first cycles was observed. However, stabilized supercapacitors showed efficiencies of 98–100 %.

Nyckelord
Graphene, Graphite, Nanofibrillated cellulose, Nanographite, Paper, Supercapacitor
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:miun:diva-22579 (URN)10.1002/pssb.201451168 (DOI)000345830900043 ()2-s2.0-84914820272 (Scopus ID)
Tillgänglig från: 2014-08-18 Skapad: 2014-08-18 Senast uppdaterad: 2019-05-02Bibliografiskt granskad
3. Large-Scale Production of Nanographite by Tube-Shear Exfoliation in Water
Öppna denna publikation i ny flik eller fönster >>Large-Scale Production of Nanographite by Tube-Shear Exfoliation in Water
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2016 (Engelska)Ingår i: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, nr 4, artikel-id e0154686Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The number of applications based on graphene, few-layer graphene, and nanographite is rapidly increasing. A large-scale process for production of these materials is critically needed to achieve cost-effective commercial products. Here, we present a novel process to mechanically exfoliate industrial quantities of nanographite from graphite in an aqueous environment with low energy consumption and at controlled shear conditions. This process, based on hydrodynamic tube shearing, produced nanometer-thick and micrometer-wide flakes of nanographite with a production rate exceeding 500 gh-1 with an energy consumption about 10 Whg-1. In addition, to facilitate large-area coating, we show that the nanographite can be mixed with nanofibrillated cellulose in the process to form highly conductive, robust and environmentally friendly composites. This composite has a sheet resistance below 1.75 Ω/sq and an electrical resistivity of 1.39×10-4 Ωm and may find use in several applications, from supercapacitors and batteries to printed electronics and solar cells. A batch of 100 liter was processed in less than 4 hours. The design of the process allow scaling to even larger volumes and the low energy consumption indicates a low-cost process.

Ort, förlag, år, upplaga, sidor
Nicklas Blomquist, 2016
Nyckelord
Nano-graphite, Graphite, Graphene, Nanomaterials, Composite materials
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:miun:diva-27600 (URN)10.1371/journal.pone.0154686 (DOI)000375212600060 ()2-s2.0-84966389426 (Scopus ID)
Projekt
KEPS
Forskningsfinansiär
Energimyndigheten
Tillgänglig från: 2016-05-09 Skapad: 2016-05-09 Senast uppdaterad: 2019-05-02Bibliografiskt granskad
4. Electrode Mass Balancing as an Inexpensive and Simple Method to Increase the Capacitance of Electric Double-Layer Capacitors
Öppna denna publikation i ny flik eller fönster >>Electrode Mass Balancing as an Inexpensive and Simple Method to Increase the Capacitance of Electric Double-Layer Capacitors
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2016 (Engelska)Ingår i: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, nr 9, s. 1-12, artikel-id e0163146Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Symmetric electric double-layer capacitors (EDLCs) have equal masses of the same active material in both electrodes. However, having equal electrode masses may prevent the EDLC to have the largest possible specific capacitance if the sizes of the hydrated anions and cations in the electrolyte differ because the electrodes and the electrolyte may not be completely utilized. Here we demonstrate how this issue can be resolved by mass balancing. If the electrode masses are adjusted according to the size of the ions, one can easily increase an EDLC's specific capacitance. To that end, we performed galvanostatic cycling to measure the capacitances of symmetric EDLCs with different electrode mass ratios using four aqueous electrolytes-Na2SO4, H2SO4, NaOH, and KOH (all with a concentration of 1 M)-and compared these to the theoretical optimal electrode mass ratio that we calculated using the sizes of the hydrated ions. Both the theoretical and experimental values revealed lower-than-1 optimal electrode ratios for all electrolytes except KOH. The largest increase in capacitance was obtained for EDLCs with NaOH as electrolyte. Specifically, we demonstrate an increase of the specific capacitance by 8.6% by adjusting the electrode mass ratio from 1 to 0.86. Our findings demonstrate that electrode mass balancing is a simple and inexpensive method to increase the capacitance of EDLCs. Furthermore, our results imply that one can reduce the amount of unused material in EDLCs and thus decrease their weight, volume and cost.

Nyckelord
Mass balancing, capacitance, electric double layer capacitor, EDLC, electrode, electrolyte, electrode mass ratio, ion size ratio
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:miun:diva-29083 (URN)10.1371/journal.pone.0163146 (DOI)000383893200073 ()2-s2.0-84992186879 (Scopus ID)
Tillgänglig från: 2016-10-10 Skapad: 2016-10-10 Senast uppdaterad: 2017-11-30Bibliografiskt granskad
5. Metal-free supercapacitor with aqueous electrolyte and low-cost carbon materials
Öppna denna publikation i ny flik eller fönster >>Metal-free supercapacitor with aqueous electrolyte and low-cost carbon materials
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2017 (Engelska)Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, artikel-id 39836Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Electric double-layer capacitors (EDLCs) or supercapacitors (SCs) are fast energy storage devices with high pulse efficiency and superior cyclability, which makes them useful in various applications including electronics, vehicles and grids. Aqueous SCs are considered to be more environmentally friendly than those based on organic electrolytes. Because of the corrosive nature of the aqueous environment, however, expensive electrochemically stable materials are needed for the current collectors and electrodes in aqueous SCs. This results in high costs for a given energy-storage capacity. To address this, we developed a novel low-cost aqueous SC using graphite foil as the current collector and a mix of graphene, nanographite, simple water-purification carbons and nanocellulose as electrodes. The electrodes were coated directly onto the graphite foil by using casting frames and the SCs were assembled in a pouch cell design. With this approach, we achieved a material cost reduction of greater than 90% while maintaining approximately one-half of the specific capacitance of a commercial unit, thus demonstrating that the proposed SC can be an environmentally friendly, low-cost alternative to conventional SCs.

Ort, förlag, år, upplaga, sidor
Nature Publishing Group, 2017
Nyckelord
Supercapacitor, EDLC, Graphene, Graphite, Nanoparticles
Nationell ämneskategori
Kompositmaterial och -teknik Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:miun:diva-29827 (URN)10.1038/srep39836 (DOI)000391182900001 ()2-s2.0-85008701942 (Scopus ID)
Forskningsfinansiär
Energimyndigheten
Anmärkning

Published online:05 January 2017

Tillgänglig från: 2017-01-06 Skapad: 2017-01-06 Senast uppdaterad: 2019-05-02Bibliografiskt granskad
6. Cellulose binders for electric double-layer capacitor electrodes: The influence of cellulose quality on electrical properties
Öppna denna publikation i ny flik eller fönster >>Cellulose binders for electric double-layer capacitor electrodes: The influence of cellulose quality on electrical properties
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2018 (Engelska)Ingår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 141, s. 342-349Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Cellulose derivatives are widely used as binders and dispersing agents in different applications. Binders composed of cellulose are an environmentally friendly alternative to oil-based polymer binding agents. Previously, we reported the use of cellulose nanofibers (CNFs) as binders in electrodes for electric double-layer capacitors (EDLCs). In addition to good mechanical stability, we demonstrated that CNFs enhanced the electrical performance of the electrodes. However, cellulose fibers can cover a broad range of length scales, and the quality requirements from an electrode perspective have not been thoroughly investigated. To evaluate the influence of fiber quality on electrode properties, we tested seven samples with different fiber dimensions that are based on the same kraft pulp. To capture the length scale from fibers to nanofibrils, we evaluated the performance of the untreated kraft pulp, refined fibers, microfibrillated cellulose (MFC) and CNFs. Electrodes with kraft pulp or refined fibers showed the lowest electrical resistivity. The specific capacitances of all EDLCs were surprisingly similar, but slightly lower for the EDLC with CNFs. The same electrode sample with CNFs also showed a slightly higher equivalent series resistance (ESR), compared to those of the other EDLCs. Graphite dispersions with MFC showed the best dispersion stability. 

Nyckelord
Cellulose, Electric double-layer capacitor, Graphite, Nanocellulose, Nanocomposite, Supercapacitor
Nationell ämneskategori
Kemiteknik
Identifikatorer
urn:nbn:se:miun:diva-32766 (URN)10.1016/j.matdes.2017.12.041 (DOI)000424945300031 ()2-s2.0-85040002856 (Scopus ID)
Tillgänglig från: 2018-01-30 Skapad: 2018-01-30 Senast uppdaterad: 2018-07-19Bibliografiskt granskad

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