Synthesis and characterization of novel carbon electrodes for high power density electrochemical capacitors
Date
2022-02-24
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Abstract
Viimastel aastatel on üsna kiiresti kasvanud nõudlus mitmekülgsete energiasalvestussüsteemide järele. Mõnedes piirkondades on pidevalt suurenev energiatarbimine ja selle mõju keskkonnale on tekitanud vajaduse uute suure võimsuse- ja energiatihedusega energiasalvestite järele. Superkondensaatorid on pälvinud palju tähelepanu, kuna neil on suur erimahtuvus, pikk tööiga, suur võimsustihedus ja väga madalad hoolduskulud. Superkondensaatoreid saab kombineerida koos kõrge energiatihedusega patareide ja kütuseelementidega erinevates rakendustes, kus on oluline samaaegselt nii suur energia kui ka võimsustihedus. Superkondensaatorites salvestatava kui ka sealt vabaneva energia väärtused sõltuvad olulisel määral selle elektrilisest mahtuvusest, süsteemi takistusest ja maksimaalsest rakupotentsiaalist, mis kõik sõltuvad kasutatavate elektroodide materjalide poorsusest ja elektrolüüdi omadustest. Üks enimkasutatud elektroodimaterjale superkondensaatorites on erinevad poorsed süsinikud ja nende hulgas ka karbiidist saadud süsinikud, millede korral on võimalik pooride suurust väga kontrollitult varieerida ning läbi selle suurendada süsteemis salvestatava energia hulka. Teiseks oluliseks energia salvestamist piiravaks teguriks superkondensaatorites on kasutatavate elektrolüütide mõõdukas tööpotentsiaal. Superkondensaatori suurepärase jõudluse saavutamiseks on seega oluline optimeerida nii elektroodimaterjali mikro- ja mesopoorsust ja selle sobivust kasutatava elektrolüüdiga kui ka optimeerida kasutatava elektrolüüdi korral selle maksimaalset rakendatavat rakupotentsiaali.
Antud doktoritöös kasutati mikro- ja mesopoorsete elektroodimaterjalide valmistamiseks sool-geel meetodit, mis annab esialgsele karbiidile täiendava mesopoorsuse, mis jääb alles ka karbiidset päritolu süsinikmaterjali ja mida ei eksisteeri kommertsiaalsest karbiidist süsteesitud süsinikus. Teiseks töötati välja ″operando″ aktiveerimise ja passiveerimise meetod elektroodide maksimaalse rakendatava rakupotsntsiaali suurendamiseks, et suurendada süsteemi energiatihedust.
In recent years, the demand for versatile energy storage systems has risen quite fast. The environmental impact of energy consumption for some regions has additionally increased the necessity for new energy storage devices with high power and energy densities. Supercapacitors have gained much attention because they have high specific capacitance, long cycle life, high power density, and very low maintenance costs. Supercapacitors complement batteries and fuel cells in applications where high power is important. The energy storage and power delivery characteristics of supercapacitors are largely determined by the electrical capacitance, system resistance, and maximum cell potential which are all dependent on the electrode materials porosity and electrolyte properties used. One of the most used electrode materials in supercapacitors are different carbide derived carbons, which have the possibility to fine-tune the pore size. One limiting factor in achieving high power density is the moderate working cell potential of different electrolytes that are used in supercapacitors. To achieve excellent performance of a supercapacitor it is important to optimize the electrode’s micro-mesoporosity and for the used electrolyte, it is important that it has a high electrochemical window and that the electrolyte ions suit the selected electrode material. In this thesis, firstly, a sol-gel method was used for the preparation of well developed micro- and mesoporous electrodes, which gives additional mesoporosity to the initial carbide material. This results also in the derived carbon material, unlike when the commercially synthesized titanium carbide is used. Secondly, the operando activation and passivation method was developed for future enlargement of the ideal polarizability region of electrodes, to achieve higher energy densities.
In recent years, the demand for versatile energy storage systems has risen quite fast. The environmental impact of energy consumption for some regions has additionally increased the necessity for new energy storage devices with high power and energy densities. Supercapacitors have gained much attention because they have high specific capacitance, long cycle life, high power density, and very low maintenance costs. Supercapacitors complement batteries and fuel cells in applications where high power is important. The energy storage and power delivery characteristics of supercapacitors are largely determined by the electrical capacitance, system resistance, and maximum cell potential which are all dependent on the electrode materials porosity and electrolyte properties used. One of the most used electrode materials in supercapacitors are different carbide derived carbons, which have the possibility to fine-tune the pore size. One limiting factor in achieving high power density is the moderate working cell potential of different electrolytes that are used in supercapacitors. To achieve excellent performance of a supercapacitor it is important to optimize the electrode’s micro-mesoporosity and for the used electrolyte, it is important that it has a high electrochemical window and that the electrolyte ions suit the selected electrode material. In this thesis, firstly, a sol-gel method was used for the preparation of well developed micro- and mesoporous electrodes, which gives additional mesoporosity to the initial carbide material. This results also in the derived carbon material, unlike when the commercially synthesized titanium carbide is used. Secondly, the operando activation and passivation method was developed for future enlargement of the ideal polarizability region of electrodes, to achieve higher energy densities.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone
Keywords
carbon materials, chemical synthesis, sol-gel processes, supercapacitors