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Enhanced electrical and mechanical properties of nanographite electrodes for supercapacitors by addition of nanofibrillated cellulose
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.ORCID iD: 0000-0002-4303-2585
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2014 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 251, no 12, 2581-2586 p.Article in journal (Refereed) 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 %.

Place, publisher, year, edition, pages
2014. Vol. 251, no 12, 2581-2586 p.
Keyword [en]
Graphene, Graphite, Nanofibrillated cellulose, Nanographite, Paper, Supercapacitor
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:miun:diva-22579DOI: 10.1002/pssb.201451168ISI: 000345830900043Scopus ID: 2-s2.0-84914820272OAI: oai:DiVA.org:miun-22579DiVA: diva2:738308
Available from: 2014-08-18 Created: 2014-08-18 Last updated: 2017-09-04Bibliographically approved
In thesis
1. Paper-based Supercapacitors
Open this publication in new window or tab >>Paper-based Supercapacitors
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The growing market of mobile electronic devices, renewable off-grid energy sources and electric vehicles requires high-performance energy storage devices. Rechargeable batteries are usually the first choice due to their high energy density. However, supercapacitors have a higher power density and longer life-time compared to batteries. For some applications supercapacitors are more suitable than batteries. They can also be used to complement batteries in order to extend a battery's life-time. The use of supercapacitors is, however, still limited due to their high costs. Most commercially available supercapacitors contain expensive electrolytes and costly electrode materials.

In this thesis I will present the concept of cost efficient, paper-based supercapacitors. The idea is to produce supercapacitors with low-cost, green materials and inexpensive production processes. We show that supercapacitor electrodes can be produced by coating graphite on paper. Roll-to-roll techniques known from the paper industry can be employed to facilitate an economic large-scale production. We investigated the influence of paper on the supercapacitor's performance and discussed its role as passive component. Furthermore, we used chemically reduced graphite oxide (CRGO) and a CRGO-gold nanoparticle composite to produce electrodes for supercapacitors. The highest specific capacitance was achieved with the CRGO-gold nanoparticle electrodes. However, materials produced by chemical synthesis and intercalation of nanoparticles are too costly for a large-scale production of inexpensive supercapacitor electrodes. Therefore, we introduced the idea of producing graphene and similar nano-sized materials in a high-pressure homogenizer. Layered materials like graphite can be exfoliated when subjected to high shear forces. In order to form mechanical stable electrodes, binders need to be added. Nanofibrillated cellulose (NFC) can be used as binder to improve the mechanical stability of the porous electrodes. Furthermore, NFC can be prepared in a high-pressure homogenizer and we aim to produce both NFC and graphene simultaneously to obtain a NFC-graphene composite. The addition of 10% NFC in ratio to the amount of graphite, increased the supercapacitor's capacitance, enhanced the dispersion stability of homogenized graphite and improved the mechanical stability of graphite electrodes in both dry and wet conditions. Scanning electron microscope images of the electrode's cross section revealed that NFC changed the internal structure of graphite electrodes depending on the type of graphite used. Thus, we discussed the influence of NFC and the electrode structure on the capacitance of supercapacitors.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2014. 65 p.
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 112
Keyword
graphene, graphite, paper, nano fibrillated cellulose, supercapacitor, electric double-layer capacitor, energy storage, roll-to-roll, coating, kinetic energy recovery
National Category
Physical Sciences
Identifiers
urn:nbn:se:miun:diva-22410 (URN)978-91-87557-68-2 (ISBN)
Presentation
2014-06-12, O 102, Mid Sweden University, Holmgatan 10, Sundsvall, 10:15 (English)
Opponent
Supervisors
Available from: 2014-08-18 Created: 2014-07-03 Last updated: 2015-03-13Bibliographically approved
2. Low-Cost, Environmentally Friendly Electric Double-Layer Capacitors: Conept, Materials and Production
Open this publication in new window or tab >>Low-Cost, Environmentally Friendly Electric Double-Layer Capacitors: Conept, Materials and Production
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2017. 157 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 267
Keyword
Electric Double-Layer Capacitor, Graphite, Cellulose Nanofibers, Large-Scale, Mass Balancing, Metal-Free
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:miun:diva-31539 (URN)978-91-88527-23-3 (ISBN)
Public defence
2017-09-08, M102, Holmgatan 10, Sundsvall, 10:15 (English)
Supervisors
Note

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.

Available from: 2017-09-07 Created: 2017-09-04 Last updated: 2017-09-07Bibliographically approved

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