(A) design of porous organic materials for electrochemical energy storage applications

Abstract

Recently, due to the diversification and upscaling of electronic devices and the trend towards electrification of various equipment, electrochemical energy storage devices are being utilized in a wide range of fields, not only in portable electronic devices and electric vehicles but also in industrial and specialized purposes. With the increasing demands of electric vehicles, the market for electrochemical energy storage devices is expected to grow explosively each year, making research into materials with higher energy storage capabilities and excellent lifespan characteristics essential. Various types of electrochemical energy storage materials are being researched, but porous materials in particular are receiving attention due to their internal pore structure and excellent physical and chemical characteristics. Porous materials are characterized by their large specific surface area, which can provide abundant active sites for electrochemical reactions, and their tunability, which allows for the control of pore size and modification of surface characteristics to provide structures more suitable for electrochemical reactions. This dissertation deals with three studies that design porous organic materials suitable for various electrochemical energy storage reactions and apply them to hybrid capacitors, batteries, and solid-state batteries. The first study focused on synthesizing carbon materials with a high surface area through the control of reactants during the polymerization process. During the polymerization of Resorcinol-Formaldehyde resin, the addition of melamine resulted in the formation of a coiled conformation of resins as opposed to the linear conformation of conventional resins. When this resin was carbonized to synthesize porous carbon material, it was found that the carbon material from the coiled conformation resin formed a larger specific surface area than linear conformation resin. The synthesized porous carbon material was used as the cathode material for a hybrid lithium-ion capacitor. Furthermore, molecular-level germanium metal particles were embedded on the support of porous carbon material as the anode, and using both materials as cathode and anode, a hybrid lithium-ion capacitor with high energy density and power density was realized. The second study focuses on the carbonization process of organic materials with control over the activation agents to form a carbon material with a high volume of pores and heteroatom doping. In this study, a neutral condition activation agent treatment combining potassium hydroxide and phosphoric acid was reported differently from conventional methods, which did not damage the organic precursor and through carbonization, a carbon material with high specific surface area and phosphorus heteroatom doping was synthesized. The network structure of this porous carbon material was utilized as the cathode material for a hybrid sodium-ion capacitor. Additionally, the porous carbon material was embedded with tin oxide through a hydrothermal synthesis reaction and used as a sodium-ion storage cathode material. Both the cathode and anode were used as electrode materials for a hybrid sodium-ion capacitor, confirming the realization of high energy and power density. The third study is on the synthesis of solid composite electrolytes using interconnected porous Metal-Organic Frameworks (MOFs) as nanofillers. To form a continuous ion conduction pathway, a network structure of MOFs connected to an organic fiber structure was synthesized and used as nanofillers to form a polymer composite solid electrolyte. The open metal sites of the MOFs showed an effect of immobilizing anions, significantly increasing the ion conductivity within the composite electrolyte and generating a fast ion transport reaction. The synthesized composite electrolyte was confirmed to be applicable not only in lithium metal batteries but also in full cells using commercialized lithium iron phosphate (LiFePO4) cathodes.