Year

2019

Degree Name

Doctor of Philosophy

Department

Institute for Superconducting and Electronic Materials

Abstract

Sodium-ion batteries (SIBs) have been deemed a promising low-cost battery technology for grid-scale energy storage in view of the abundance of sodium resources. The large ionic size (1.02 Å) and different electronegativity of Na+ nevertheless, make it difficult to reversibly insert/extract into/out of most host materials, resulting in inferior battery performance. Searching for viable anode materials with high efficiency that can accommodate the Na+ while achieving long-term stable electrochemical performance is a tough issue for SIBs. With the characteristics of high theoretical capacity (335 mAh g-1), reasonable insertion voltage (~0.75 V vs. Na/Na+), chemical stability, and abundant reserves, titanium oxides have shown promise as anodes for SIBs. The slow progress on titania-based SIBs, however, has been due mainly to their inferior conductivity and sluggish Na+ reaction kinetics. In this doctoral work, several strategies, including atomic-level P-doping, surface structural engineering, constructing two dimensional (2D) superlattices, and optimizing Na+ intercalation kinetics by tailoring-designed nanostructures, have been investigated to enhance the electrochemical reactivity of titania anodes.

Structural modulation and surface engineering have remarkable advantages for fast and efficient charge storage. In Chapter 4, a phosphorus modulation strategy is presented that can induce surface structural-disorder while realizing interior phosphorus-doping to enhance the Na+ storage capability of TiO2. The P-modulated TiO2 nanocrystals present an improved structural stability and Na+ diffusion kinetics, achieving excellent high rate performance and long cycling life without dramatically capacity fading, even after 5000 cycles at a current density of 30 C. Meanwhile, the Na+ insertion mechanism was symmetrically studied using in situ synchrotron X-ray diffraction (XRD). The results show that the phosphorus modulation strategy can enable negligible volume expansion of only 0.1% during cycling.

FoR codes (2008)

0912 MATERIALS ENGINEERING, 0904 CHEMICAL ENGINEERING, 0302 INORGANIC CHEMISTRY, 1007 NANOTECHNOLOGY

Download

Share

COinS
 

Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.