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.
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