title: Exploring Functional Organic Materials for High-Performance Rechargeable Batteries
Creators: name: Wu, Zhenzhen
Publisher: name: Griffith University
Year: 2021
Subjects: subject: Organic materials
subject: sustainable energy storage
subject: energy storage
subject: Molecular
subject: morphological engineering
subject: developing advanced OEMs

description: This success of Li-ion batteries (LIBs) is mainly built on inorganic electrode materials (IEMs). However, due to the inherent drawbacks of IEMs, such as short lifetime, potential fire risk, heavy dependence on unsustainable natural sources and energy in the course of mining (such as Li, Co and Ni), and high carbon footprint production processes, we must explore the use of other materials. Organic materials (OMs) can be fabricated from abundant and renewable natural sources and achieve sustainable energy storage. These materials can be used as organic electrode materials (OEMs) and organic additives (OAs) in modern metal ion batteries (MIBs). OMs can deliver remarkable battery performance for MIBs due to their unique molecular versatility, high flexibility, versatile structures, sustainable organic resources, and low environmental cost. Before OEMs can be widely used in MIBs, their inherent issues such as low intrinsic electronic conductivity, significant solubility in electrolytes, large volume change, and low tap density must be addressed. In this thesis, the potential roles, energy storage mechanisms, existing challenges, and possible solutions to these challenges are systematically summarized using molecular and morphological engineering. Molecular and morphological engineering could offer practical pathways for developing advanced OEMs in next-generation rechargeable MIBs. Molecular engineering, such as grafting electron-withdrawing or electron-donating functional groups, increasing various redox-active sites, extending conductive networks, and increasing the degree of polymerization, could enhance the electrochemical performance including specific capacity (such as voltage output and charge transfer number), rate capability, and cycling stability. Morphological engineering facilitates the preparation of different dimensional OEMs (inc uding 0D, 1D, 2D, and 3D OEMs) via bottom-up and top-down methods to enhance electrons/ions diffusion kinetics at the OEMs and stabilize the electrode structure. Recent progress of metal-organic polymers (MOPs), a category of OEM is also systematically and independently reviewed. Cyanuric acid (CA) and trithiocyanuric acid (TTCA), two typical OEMs of imide and thioimide, with small molecular size, are used as cathode materials in LIBs. I theoretically and experimentally demonstrated that H-transfer mechanism is responsible for the high capacities of 464.6 and 820.6 mAh g-1 for CA and TTCA cathodes, respectively. This work inspires us to explore more organic reaction mechanism for energy storage application in MIBs. To demonstrate the effectiveness of relatively large organic molecules for LIBs applications, a Cu (II) salt and benzenehexathiolate (BHT) were used as the precursors for the synthesis of robust and redox-active 2D MOFs (or called MOPs) materials, i.e., [Cu3(C6S6)]n, namely Cu-BHT. The Cu-BHT MOFs have a highly conjugated structure, affording a high electronic conductivity of 231 S cm-1 that could further be increased upon lithiation in lithium-ion battery (LIB) applications. A reversible 4-electrons reaction reveals the Li storage mechanism of the Cu-BHT for a theoretical capacity of 236 mAh g-1. The as-prepared Cu-BHT cathode delivers an excellent reversible capacity of 175 mAh g-1 with ultra-low capacity deterioration (0.048% per cycle) upon 500 cycles at a high current density of 300 mA g-1. Poly(TEMPO-acrylamide) (PTAm) is synthesized as an OEM for potassium dual-ions batteries (KDIBs). Long chain PTAm is subject to a carbon nanotubes (CNTs) assisted morphological engineering process to produce a nanostructured composite, namely PTAm@CNTs. The asprepared PTAm@CNTs nanocomposite possesses significant surface area and pores, excellent electronic conductivity and exceptional ionic transfer at the redox active sites (i.e., thenitroxyl radicals N-O.). These design facilitate the as-prepared PTAm@CNTs cathode to efficiently and reversibly adsorb/desorb PF6- ions in KDIBs, delivering high energy density, rate capability and robust cycling stability. As a result, the PTAm@CNTs present an excellent specific capacity of 108 mAh g-1 at 2 A g-1 (equal to 16.8C, 1C=119 mAh g-1), an outstanding capacity around 49 mAh g-1 at the high rate of 33.6 C, and a long cycling life-span up to 400 time. Functional organic compounds could be an effective additive to address the critical problems of electrochemical energy storage devices, such as MIBs. In this thesis, I designed and used cyclohexanedodecol (CHD) in ZnSO4 aqueous electrolyte solution in an aqueous zinc ion batteries (AZIBs). CHD could serves two functions. Firstly, in the aqueous electrolyte, CHD reacts with the hydrated Zn(H2O)6 2+ structure and forms new complex hydrated ions, mainly [Zn(H2O)5(CHD)]2+, to facilitate rapid desolvation in the course of electrochemical Zn plating. Secondly, at the surface of the Zn anode, CHD could be readily adsorbed onto the Zn anode and build protection and a supporting layer, which not only facilitates the even and efficient adsorption of [Zn(H2O)5(CHD)]2+ and the electrochemical plating process, but also prevents the occurrence of the HER reaction and formation of the passivation layer. Due to the efficient functions of the proposed CHD electrolyte additive, long cycling life and high coulombic efficiency are achieved.