Nanomaterials as Effective Electrodes for High-performance Supercapacitors

用於高性能超級電容器高效電極的納米材料研究

Student thesis: Doctoral Thesis

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Award date16 Aug 2023

Abstract

Energy storage devices play an important role in our daily lives. Among various energy storage gadgets, supercapacitor (SC) has received considerable attention in the past decades due to its high power density, excellent cycle life, and fast charge discharge. Although, a lot of research has been conducted to enhance its energy density without scarifying its power density and cycle life. Numerous parameters such as capacitance/capacity, cycle life, rate capability, diffusions rates of electrolyte ions, conductivity, volume changing during electrochemical measurements, energy and power densities, cost, practicality, abundance in resources, simplicity, safety, and scalable preparation are necessary to be considered for SCs. So, extensive research has been devoted to obtain new and optimized electrode materials, electrolytes, substrates, binders, and separators to achieve decent performance of SCs.

This thesis focuses on the investigation of the positive/negative/hybrid electrode materials, substrates, and electrolytes to satisfy the requirement of the clean and reliable SCs. In chapter 1, we have discussed background, scope, problem statement, and research contributions. In chapter 2, we have provided detailed literature review about the history of SCs, substrates/current collectors, types of active electrode materials, separators, electrolytes, mechanism, different structures, and device types and the assembly. The detail experimental approaches of each chapter have been summarized in chapter 3. Chapter 4 presented the insertion of 2D nanosheets in 1D nanowires based on metal oxides for fast ion transport, resulting excellent electrochemical performance in three- as well as two-electrode setup. In chapter 5 we have suggested laboratory waste papers and boxes in energy storage as flexible, lightweight, and cost-effective substrates. This work also contributed to the reduction of waste paper trash generation. In chapter 6, we have theoretically and experimentally studied the polyhedral PO4 anions based trimetallic phosphate which displayed excellent conductivity, lower IR drop, higher Coulombic efficiency and higher capacity than binary and single metal phosphate. In chapter 7, we have suggested an effective approach to avoid random orientations and poor conductivity of metal-organic frameworks (MOFs). We have prepared solution-free, dry-oxidative, and binder-free p-type CuO nanowires to offer the orientation to the n-type MOF and avoid agglomeration of the MOFs. To widen the potential window and enhance the cycling performance of the MOF integrated CuO, we theoretically and experimentally studied the in-situ incorporation of MOF-derived Zr-Mn-oxide in solution-free CuO nanowires (chapter 8). The oriented Zr-Mn-oxide@CuO not only avoided the structural limitations of MOF but also used as a positive-negative hybrid electrode material in aqueous medium. In chapter 9 and 10, we did not only avoid the structural limitations of MOF but also provided a solution to low conductivity, poor stability, aggregation, and poor active-sites of transition metal chalcogenides (TMCs). In these chapters, the in-situ grown MOF on CuO nanowires was converted to oriented and directional TMCs, resulting decent stability, capacity, and conductivity of TMCs@CuO. In chapter 11, we summarized the thesis and proposed future aspects.

Overall, the thesis not only covered many aspects related to SCs but also clarified misconceptions/misinterpretation in thermal terminologies; charge storage mechanism; symmetric, asymmetric, and hybrid devices; and the equations used for different calculations in SCs.