New methods to synthesize nanosized oxides for energy storage applications

• Main Author: Ng, Vincent Ming Hong
• Other Authors: Xu Zhichuan Jason
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Materials::Energy materials; DRNTU::Engineering::Materials::Nanostructured materials
• Online Access: https://hdl.handle.net/10356/89329; http://hdl.handle.net/10220/47699
• Institution: Nanyang Technological University

The proliferation of portable consumer electronics has been built upon the breakthrough in electrode materials for rechargeable electrochemical energy storage — coinciding with the advent of lithium-ion batteries (LIBs) technology. Coupled with the lifestyles of the burgeoning global population becoming more energy intensive, it has evolved into both a technological and societal demand for the development of more cost-efficient and durable batteries. The consensual approach towards tackling intermittency of renewable energy sources and improving the competitiveness of electric vehicles necessitates an energy storage system to reversibly uptake and release greater quantity of charges and to reliably do so at a much faster rate. However, the incumbent graphitic anode material in existing commercialized LIBs is inherently limited in both capacity (energy density) and rate performance (power density). Combined with its relative abundancy and low cost, the environmentally benign tin (IV) oxide (SnO2), which possesses alternative Li+ ions storage mechanisms beyond insertion chemistry and high theoretical gravimetric capacity of 1494 mAh g-1, is one widely studied alternative anode material for LIBs application. Nevertheless, it is generally accepted that further improvement is required to overcome its inherent poor conductivity and rapid structural degradation upon charging/discharging. Over the past years, tremendous progress in dimensional reduction, morphological variations and formation of composites have significantly enhanced electrochemical performance of SnO2-based nanostructures. However, most are prepared by complex chemical synthesis which are not feasible for scaling up to industrial production. Herein, within the context of this thesis, three approaches involving procedures with high practicality are purposefully selected for either the synthesis and modification of SnO2 to overcome the inadequacies of SnO2 as LIBs anode material. First, despite the absence of size distribution and morphological uniformity, a multi-faceted SnO2-graphite nanocomposite as-fabricated by an industrially compatible high energy mechanical milling delivers high specific capacity comparable to those by complex chemical synthesis. Second, an unorthodox and counterintuitive approach to post-treat antimony (Sb)-doped SnO2 in selected acidic etchants for partial dopant removal from SnO2 lattice has yielded significantly enhanced cyclic stability beyond those of untreated Sb-doped SnO2 (mere doping) and undoped SnO2. Analogous to void engineering by removal of sacrificial phase, this demonstrates the viability of the partial dopant removal and provides a new perspective on incorporating dopant species into semiconducting materials, such as SnO2. Third, a hierarchical Ti3C2Tx-SnO2·Co3O4 architecture with unheralded customizability of packing density was simply assembled by a mature industrial procedure of freeze-drying. The Ti3C2Tx-SnO2·Co3O4 hybrid anode exhibits exceptional cyclic stability and rate capability, beyond most MXene/transition metal oxide (TMO) that have been reported.