Organic and Polymer Structure Engineering, Characterization, and Analysis for Alkali-Ion and Redox Flow Batteries

Abstract

Lithium-ion batteries (LIBs) have been the leading source of energy storage devices for decades. Their usage and applications are immeasurable, spanning from portable electronics like phones and tablets to electric vehicles, scooters, e-bikes, and grid-scale energy storage devices. However, with ever-increasing demands for cost-effective, environmentally benign, renewable, and sustainable energy sources, commercial LIBs simply cannot satisfy these needs. Being comprised of inorganic materials such as cobalt-rich cathodes and graphite-based anodes, these batteries are unsustainable, nonrenewable, and environmentally hazardous owing to limited availability of lithium resources, and expensive, scarce, and highly toxic cobalt resources.1,2 These factors have prevented further development and large-scale applications of LIBs. Na-ion batteries (NIBs) and K-ion batteries (KIBs) are promising alternatives due to their low cost, similar electrochemistry to LIBs, and readily available sodium and potassium resources. However, employing inorganic electrode materials in NIBs and KIBs results in low capacity, sluggish reaction kinetics, and fast capacity loss (due to the larger ion size of Na+ and K+ versus Li+).3–9 Therefore, developing high-performance organic electrode materials (OEMs) is paramount for the future of renewable and sustainable energy storage. OEMs offer countless advantages for NIBs and KIBs, including lightweight, abundance, low cost, high structural tunability, high sustainability, recyclability, and universal electrochemistry in alkali-ion battery systems. This research focuses on exploring novel organic materials for NIBs and KIBs anodes, as well as investigating polymer materials for magnesium redox flow battery (MRFBs) catholytes. In my work, I employed unique organic electrode materials, 2,2’-bipyridine-4,4’-dicarboxylic acid disodium/dipotassium salts (Na-DCA/K-DCA) to investigate and explore the impacts of pyridinic nitrogen and nitrogen-doped reduced graphene oxide (NrGO) on carboxylate-based organic anodes in NIBs/KIBs in order to fully unravel the correlation between the structure of conjugated carboxylate compounds and their electrochemical performance. The results demonstrate that these anode materials can be optimized by introducing NrGO and tuning the concentration of inorganic salts in the electrolyte thereby improving cycling stability and performance in both NIBs and KIBs. To further investigate the uses of OEMs, several redox-active polymers based on 1,4,5,8-napthalenetetracarboxylic dianhydride and polyethylene glycol chains (with varying lengths) were synthesized as catholyte materials for MRFBs. While OEM dissolution is not desired in alkali-ion battery systems, these polymers were engineered specifically to be soluble in organic electrolytes and solvents for a novel redox flow battery system. The resulting polymers demonstrated exceptional electrochemical performance in MRFBs owing to their increased solubility and stability.