Spinel Oxide Hybrid Structures: Designing Battery-like Materials for High-Performance Energy Storage

Abstract

The electrochemical capacitors, also known as supercapacitors, are the next-generation energy storage devices that can store the energy by a surface or near-surface redox reaction that enables achieving high energy density at high charge-discharge rates. Since the discovery of the “pseudocapacitive” behavior of hydrous RuO2 by Conway, there has been growing research on pseudocapacitance in other materials including metal oxides. Spinel oxides are a subcategory of transition metal oxides (TMOs) that exhibit high redox activity, however, they exhibit the electrochemical characteristics of battery-like material that does not meet the criteria for high-performance energy storage, which are potential independent charge storage and limited rate-capability. It has been suggested that the electrochemical behavior of spinel oxides, for this thesis in particular NiCo2O4, could be shifted from battery-like to pseudocapacitive by employing appropriate methods to produce nanomaterials with high surface areas and using high surface conductive structures such as graphene, CNTs, and polymers to form hybrid structures with enhanced electrochemical properties. Through my Ph.D. work, we have tried to focus on addressing solutions to charge-transport limitations and sluggish kinetics, as two key factors that hinder the practical application of spinel oxides for high-performance energy storage devices. We have developed a universal fabrication technique for hybrid structure formation as well as a novel approach to tune the spinel oxides microstructure by controlled crystallization of sacrificial templates to tackle the above-mentioned obstacles and provide perspective and possible opportunities for spinel oxide hybrid structures for practical applications in energy storage.