Year

2019

Degree Name

Doctor of Philosophy

Department

School of Mechanical, Materials, Mechatronic and Biomedical Engineering

Abstract

In the past few decades, with the continuously depletion of fossil fuels, developing renewable energy resources has become increasingly necessary. For industrial applications, energy storage devices are urgently needed for meeting the requirements of large-scale commercialization. Among them, alkaline ion batteries, especially lithium ion batteries (LIBs), have attracted great attentions due to their high energy density and comparable volumetric capacities for a variety of applications such as mobile phones and portable electrical devices. Nevertheless, LIBs seemingly cannot meet the requirements for next-stage applications such as electrical vehicles in the long run due to the high cost of lithium mineral resources. Therefore, developing alternative energy storage devices is quite important for scalable applications. Sodium ion batteries (SIBs) and potassium ion batteries (PIBs) have attracted considerable attention due to the abundant Na and K resources in the Earth’s crust. SIBs may have lower energy-density than LIBs, however, due to the relatively high standard hydrogen potential (-2.71 V vs. E° ) of Na, which is obstructing their potential application. In contrast, K has a low standard hydrogen potential (-2.93 V vs. E°), close to that of lithium (-3.04 V vs. E°), which makes the PIBs a good candidate for low-cost and high-energy-density systems.

In terms of electrode materials, carbon-based materials possess long-term cycling stability and high rate capability, making them promising anodes. Their low theoretical capacities may still be an obstacle, however, for high-energy-density energy storage devices. Among the candidate anode materials, phosphorus-based anodes for PIBs are attractive due to their competitively high energy-density compared to carbon-based anodes, based on their high theoretical capacity of 2594 mA h g-1 (formation of K3P). Nevertheless, they have poor electrochemical performance caused by relatively large volume expansion, low electrical conductivity, and severe electrolyte decomposition due to the highly reactive phosphide surface, which hinders their potential applications.

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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.