Poliimidi kot organski katodni materiali za magnezijeve akumulatorje

Bančič, Tanja (author), Dominko, Robert (mentor), Svete, Jurij (comentor)

Magnezijevi (Mg) akumulatorji so obetavni nasledniki litijevih (Li) akumulatorjev zaradi izboljšane varnosti, volumetrične kapacitete, cene in večje dostopnosti materiala. Klasični anorganski katodni materiali, kjer se kovinski ioni vgrajujejo v kristalno rešetko, se pri multivalentnih Mg ionih ne obnesejo dobro. Veliko boljša alternativa so organski katodni materiali, ki zaradi svoje odprte in prilagodljive strukture veliko lažje shranjujejo Mg ione. Glavna tema disertacije so poliimidni polimeri kot katodni materiali v Mg akumulatorjih. Na začetku smo se osredotočili na različne sintezne poti in opazovali kakšen vpliv imajo na elektrokemijsko delovanje materiala. Elektrokemijsko delovanje v bolj uveljavljenih in raziskanih Li akumulatorjih nam je služilo kot prvi pokazatelj delovanja polimera. Naslednji korak je bila sinteza novih polimerov in raziskovanje njihovega elektrokemijskega odziva v Li in Mg akumulatorjih. V zadnjem delu dizertacije smo se osredotočili na sam mehanizem elektrokemijske reakcije v Mg akumulatorjih. Delovanje poliimidov v Mg akumulatorjih smo primerjali s kinonskimi materiali in ugotavljali, ali se redoks mehanizem med različnimi skupinami polimerov razlikuje. Mehanizem shranjevanja naboja v poliimidih smo raziskovali s pomočjo in-operando infrardeče spektroskopije, ki smo jo dodatno potrdili še s pomočjo teorije gostotnih funkcionalov (DFT). Zaradi netopnosti poliimidov smo bili znatno omejeni z analiznimi tehnikami. Uporabili smo infrardečo spektroskopijo, jedrsko magnetno resonanco v trdnem, elementno analizo in vrstično elektronsko mikroskopijo. Pri karakterizaciji spojin smo se osredotočili tudi na potencialne nečistoče med polimernimi verigami. Ugotovili smo, da so poliimidi elektrokemijsko aktivni v Mg akumulatorjih, potrdili smo tudi njihov elektrokemijski mehanizem. Zaradi še večje kompleksnosti Mg sistema v primerjavi z Li, njihovega delovanja v vlogi katode nismo mogli temeljito opredeliti. Na celotno delovanje akumulatorja vpliva preveč med seboj tesno prepletenih in soodvisnih dejavnikov, še posebej elektrolit in njegovo občutljivo ravnovesje elektrokemijsko aktivnih kompleksov.

• Language: Slovenian
• Keywords: Mg akumulatorji, organski katodni materiali, poliimidi, polimeri, mehanizem elektrokemijske reakcije
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2022
• PID: 20.500.12556/RUL-135885
• COBISS.SI-ID: 103066115
• Publication date in RUL: 31.03.2022

Secondary language

• Language: English
• Title: Polyimides as organic cathode materials for magnesium batteries

Abstract

Mg batteries are promising post-Li battery technology due to their improved safety, volumetric capacity, price and abundance. It has been shown that traditional inorganic intercalation cathodes are not the best fit for multivalent Mg ions, while organic cathode materials seem as favorable option on account of their flexible, open structure. This thesis is about studying polyimides as cathode materials in Mg batteries. Not much data is published about polyimides as cathodes in Mg system and our goal was to explore their general Mg electrochemistry. Initially we focused on exploring various synthetic conditions and observed how it affected the electrochemical performance in a battery. Electrochemistry in Li system served us as an early indicator how a certain polymer behaves as a cathode. Besides having a better cycling performance in terms of stability, Li-organic system is more understood. The next step was synthesis and battery cycling of some novel polymers, which were not yet published at that point. In the last part of the thesis, our focus was building better understanding of electrochemical mechanism of charge storage in Mg system. We briefly compared polyimide Mg electrochemistry to quinones to see if they share similar mechanism. More detailed study of charge storage mechanism was performed by in-operando infrared spectroscopy, which was supported by density functional theory study. Because of polyimides insolubility, we were notably limited by possible analytical techniques. We used elemental analysis, infrared spectroscopy, solid-state nuclear magnetic resonance and scanning electron microscopy. Some effort was devoted to determination of possible impurities within polymer chains. Polyimides were found to be electrochemically active in Mg system, with confirmed electrochemical mechanism of carbonyl bond reduction. Mg electrochemistry is even more complex than Li and we could not thoroughly estimate role of polyimides as a cathode since there seem to be many factors, that are tightly intertwined and co-dependent, especially electrolyte and its fine balance of electroactive species.

• Keywords: Mg batteries, organic cathode materials, polyimides, polymers, electrochemical reaction mechanism