Priprava i testiranje silicijevih anoda za litij ionske galvanske članke

master's thesis

• Title (english): Preparation and testing of silicon anodes for Li-ion batteries
• Author: Vedran Petrić
• Mentor: Zoran Mandić (mentor)
• Committee member: Zoran Mandić (predsjednik povjerenstva)
• Committee member: Marijana Kraljić Roković (član povjerenstva)
• Committee member: Stjepan Milardović (član povjerenstva)
• Granter: University of Zagreb; Faculty of Chemical Engineering and Technology; Zagreb
• Defense date and country: 2019-07-10, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Chemical Engineering

Abstract

Svrha ovog rada bila je pripraviti silicijeve elektrode te ih testirati za primjenu u litij ionskim baterijama. Silicij je zanimljiv kao potencijalni anodni materijal za primjenu u Li-ion baterijama zbog svojeg velikog teorijskog kapaciteta, ~4000 mA h g^-1 i visokog radnog napona od 0,4 V vs Li/Li+. Elektrode su pripravljene miješanjem praha silicija, PVDF veziva i visoko vodljivog ugljika „carbon black“ u omjeru 60:20:20. Od dobivene smjese se napravio tanki film koji je zatim sušen i rezan u konačni oblik elektrode. Dobivene elektrode su spojene kao katode prema litijevoj anodi u „coffee bag“ galvanskom članku. Pripravljene su dva članka imenovana „PSi2“ i „PSi4“. Karakterizacija članaka provedena je elektrokemijskim tehnikama cikličke voltametrije (CV) i elektrokemijske impedancijske spektroskopije (EIS). Za članak PSi2 proveden je jedan ciklus CV od napona otvorenog kruga (OCV) do E=0,1 V uz brzinu promjene napona v=10 mV s^-1. EIS se provodio prilikom litiranja i de-litiranja u koracima od 0,5 V od početnog OCV napona do E=0,1 V i nazad. Za članak PSi4 provedeno je 6 ciklusa CV od početnog OCV do E=0,1V, v=10 mV s^-1. EIS za članak PSi4 proveden je prije cikličke voltametrije te nakon svakog od šest ciklusa pri OCV-u tako da je nakon svakog mjerenja impedancije proveden ciklus od OCV do E=0,1 V i nazad nakon čega je članak „odmarao“ 3 minute zbog uspostave ravnotežnog stanja. Nakon provedenog ispitivanja snimljene su površine pripravljenih elektroda pomoću pretražnog elektronskog mikroskopa (SEM) . Rezultati ispitivanja CV pokazali su strujne vrhove u katodnom smjeru koji se povezuju s procesom nastanka SEI sloja i procesom litiranja elektrode. U anodnom smjeru se vide strujni vrhovi koji se povezuju sa de-litiranjem elektrode. Primijećeno je smanjenje katodne struje i porast anodne struje svakim provedenim ciklusom. Rezultati EIS pri visokim naponima, E > 1,0 V prikazuju linearni rast imaginarnog i realnog dijela impedancije sa smanjenjem frekvencije. Pri nižim n, E < 0,5 V se primjećuje ponašanje karakteristično za litij ionske baterije te kinetički polukrug koji se pripisuje nastanku SEI sloja. Karakterizacija površine je pokazala puknuća u strukturi elektrode koja se mogu pripisati promjeni volumena prilikom litiranja i de-litiranja.

Abstract (english)

The purpose of this paper was to construct and test silicon electrodes for their application in lithium ion batteries. Silicon is an interesting anode material for Li-ion batteries due to its large theoretical capacity, ~4000 mA h g^-1, and a high working voltage of 0.4 V vs Li/Li+. The electrodes were constructed by mixing silicon powder, PVDF binder and highly conductive “carbon black” in the ratio of 60:20:20. The produced slurry was coated as a thin film on aluminium current collector. The electrodes were then dried and cut into the final circular shape. The prepared electrodes were assembled as cathodes in a galvanic cell against lithium anode in a “coffee bag” housing. Two galvanic cells were made, PSi2 and PSi4. The characterization of the cells was done by the electrochemical techniques of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The PSi2 cell was cycled once during CV testing from the open circuit voltage (OCV) to E=0.1 V with the scan rate of, v=10 mV s^-1. EIS was conducted during the processes of lithiation and de-lithiation in a 0.5 V steps, from OCV to E=0.1 V and back. The PSi4 cell was cycled 6 times during CV testing, from the starting OCV to E=0.1 V, v=10 mV s^-1. After each cycle EIS measurement was made at the OCV. After the CV and EIS testing, the surface of the electrode was characterized with a scanning electron microscope (SEM). The CV results show cathodic current peaks that are attributed to the formation of the SEI layer and to the process of lithiation. The anodic current shows peaks attributed to the de-lithiation process. An increase in the anodic current and a decrease in the cathodic current were noticed after every subsequent cycle. The EIS measurements showed a linear increase in the imaginary and real impedance with the decrease of frequency at higher voltages E>1.0 V. The impedance behaviour similar to lithium ion batteries was noticed at lower voltages, E<0.5 V. Also, the formation of a kinetic semicircle that is attributed to the formation of the SEI layer was noticed. Finally, surface characterization showed cracks in the electrode structure that can be attributed to the change in volume during lithiation and de-lithiation.

• Keywords: silicij; anoda; galvanski članak; Li-ion; baterija; ciklička voltametrija; elektrokemijska impedancijska spektroskopija
• Keywords (english): silicon; anode; galvanic cell; Li-ion; battery; cyclic voltammetry; electrochemical impedance spectroscopy
• Language: croatian
• URN:NBN: urn:nbn:hr:149:007574
• Study programme: Title: Applied Chemistry - Graduate study; specializations in: Environmental chemistry and green technologies, Advanced materials and technologies, Applied organic chemistry; Course: Advanced materials and technologies; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra primijenjene kemije (magistar/magistra primijenjene kemije)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2022-02-26 21:33:37