magistrsko delo
Aleksandar Blagojević (Author), Robert Dominko (Mentor), Marjan Marinšek (Thesis defence commission member), Urška Šebenik (Thesis defence commission member)

Abstract

Organske elektrode predstavljajo pomembno smer pri uveljavljanju akumulatorjev nove generacije. Njihove lastnosti, kot so nizka cena, prijaznost okolju, trajnostna vzdržnost, odlična strukturna večnamenskost in fleksibilnost, predstavljajo prednosti, ki jih delajo bolj zaželene in uporabne v primerjavi z ostalimi aktivnimi materiali. Eden takih materialov je tudi poli(hidrokinonil-benzokinonil sulfid)/CNT oz. PHBQS/CNT, ki je tema preučevanja te magistrske naloge. Polimerni nanokompozit PHBQS/CNT je zanimiv organski katodni material predvsem zaradi visoke teoretične kapacitete (382 mAh/g). Sestavljen je iz hidrokinonskih in benzokinonskih enot povezanih preko tioeterskih vezi žvepla. Dodatek ogljikovih nanocevk (CNT) izboljša njegovo električno prevodnost in približa kapaciteto teoretični vrednosti. V raziskavi smo optimizirali potrebno količino dodatka CNT. Prevelika količina namreč zmanjša energijsko gostoto materiala, s premajhnim dodatkom pa ne dobimo želenih lastnosti. Vgradnja CNT v polimerno matriko je potekala v fazi polimerizacije. S solvotermalno in situ polimerizacijsko tehniko smo uspešno sintetizirali sedem polimernih nanokompozitov PHBQS/CNT, pri čemer smo spreminjali količino dodanih CNT (0, 0,5, 0,75, 1, 5, 10 in 15 mas. %). Z elektrokemijsko impedančno spektroskopijo smo izmerili impedance in določili prevodnost vsakega polimernega nanokompozita. Zaznali smo perkolacijsko obnašanje, ki nam je omogočilo določitev koncentracije, pri kateri neprevoden polimerni nanokompozit postane električno prevoden. Kritična koncentracija (prag perkolacije), pri kateri je prišlo do povečanja električne prevodnosti za nekaj redov velikosti, je bila opažena pri dodatku 1 % CNT. To pomeni, da je za tvorbo prevodne mreže znotraj polimerne matrike potrebno dodati vsaj 1 % CNT. Elektrokemijsko učinkovitost nanokompozitov smo preverili pri, pod in nad pragom perkolacije z galvanostatskimi meritvami proti Li polčlenu. Pri vsebnosti 0 % CNT je maksimalna kapaciteta znašala 301 mAh/g. Pri pragu perkolacije je nanokompozit dosegel kapaciteto 320 mAh/g, nad pragom perkolacije (pri dodatku 5 % CNT) pa 342 mAh/g, kar predstavlja 89,5 % teoretične kapacitete polimera PHBQS. Za dobre elektrokemijske lastnosti je posledično potrebno dodati vsaj 1 % ogljikovih nanocevk. Za najbolj optimalne elektrokemijske zmogljivosti pa jih je potrebno dodati še nekaj odstotkov nad pragom perkolacije.

Keywords

akumulatorji;polimeri;PHBQS;ogljikove nanocevke;CNT;nanokompoziti;prag perkolacije;organski katodni materiali;magistrska dela;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL FKKT - Faculty of Chemistry and Chemical Technology
Publisher: [A. Blagojević]
UDC: 621.355:620.3(043.2)
COBISS: 54376195 Link will open in a new window
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Other data

Secondary language: English
Secondary title: Optimization of electrochemical properties in PHBQS/CNT nanocomposites
Secondary abstract: Organic electrodes represent an important direction in the implementation of new generation batteries. Their properties – such as low cost, environmental friendliness, sustainability, excellent structural versatility and flexibility – represent advantages that make them more desirable and useful compared to other active materials. An example of such a material is poly(hydroquinonyl-benzoquinonyl sulfide)/CNT or PHBQS/CNT, which is also the topic of the study of this master's thesis. Polymer nanocomposite PHBQS/CNT is an interesting organic cathode material mainly due to its high theoretical capacity (382 mAh/g). It consists of hydroquinone and benzoquinone units which are linked by the thioether bonds. The addition of the carbon nanotubes (CNTs) improves the electrical conductivity of this material and brings its capacity closer to the theoretical value. In the study, we optimized the required amount of the additive. Adding too big amount of the CNTs reduces the material's energy density, whereas insufficient addition does not give us the desired properties. The incorporation of the CNTs into the polymer matrix took place in the polymerization phase. Seven PHBQS/CNT polymer nanocomposites with different amount of added CNTs (0, 0.5, 0.75, 1, 5, 10 and 15 wt%) were successfully synthesized by the solvothermal in situ polymerization technique. We used the electrochemical impedance spectroscopy method for measuring the impedances and determining the conductivity of each polymer nanocomposite. Percolation behaviour was observed, which allowed us to determine the concentration at which a non-conductive polymer nanocomposite becomes electrically conductive. The critical concentration (percolation threshold) at which there was an increase in electrical conductivity by several orders of magnitude was observed at 1% addition of CNTs. This means that at least 1% of CNTs must be added to form a conductive network within the polymer matrix. The electrochemical performance of nanocomposites was analysed at, below and above the percolation threshold by galvanostatic measurements versus Li half-cell. At 0% of CNTs content, the maximum capacity was 301 mAh/g. At the percolation threshold, the nanocomposite reached the maximum capacity of 320 mAh/g, whereas above the percolation threshold (at 5% CNTs content) the maximum capacity was 342 mAh/g, which represents 89,5% of the theoretical capacity of the PHBQS polymer. As a result, at least 1% of the carbon nanotubes needs to be added for good electrochemical properties. For the most optimal electrochemical performance, it is necessary to add them a few percent above the percolation threshold.
Secondary keywords: batteries;PHBQS;CNT;percolation threshold;organic cathode materials;
Type (COBISS): Master's thesis/paper
Study programme: 1000376
Thesis comment: Univ. v Ljubljani, Fak. za kemijo in kemijsko tehnologijo, smer Kemijsko inženirstvo
Pages: 58 str.
ID: 12625093