Year

2021

Degree Name

Doctor of Philosophy

Department

Institute for Superconducting and Electronic Materials

Abstract

With the worldwide rapidly growing demand for energy, non-renewable traditional fossil fuels such as coal, oil, and gas are facing the situation of depletion. Clean and renewable energy resources such as solar energy, wind energy and tide energy are among the most abundant and potentially available resource to take place of the fossil fuels in the future.

These renewable energy sources are not constant and they are limited as to locations. Therefore, electrical energy storage (EES) devices must be combined with these renewable forms of energy. Rechargeable lithium-ion batteries (LIBs) are high energy electrical energy storage devices, which have been commercialized for around three decades. They are not only used with naturally clean renewable energy resources, but also ubiquitous consumer electronic devices such as cell phones, electrical cars, and laptop computers. Because of the high cost of the lithium resources, it is an urgent necessity to develop alternatives to LIBs with comparable performance.

Sodium ion batteries (SIBs) and potassium ion batteries (PIBs) are possible alternatives to LIBs due to the richer sodium and potassium resources in the earth’s crust. The richer resources of SIBs and PIBs give them have lower prices compared to LIBs. The prices of sodium carbonate and potassium carbonate are similar, and they are much lower than the price of lithium carbonate, which is the precursor for making LIBs.This makes SIBs and PIBs cheaper to the LIBs. In addition, cheaper aluminum can be used as current collectors instead of copper in PIBs and SIBs, since Al-K and Al-Na alloys will not form at room temperature which also flows through to lower the price of sodium and potassium ion batteries.

In spite of the lower prices of PIBs and SIBs, their disadvantages are obvious. The radii of the sodium ion and the potassium ion are much larger compared to the lithium-ion radius, which results in the larger volume change during the discharge and charge processes. Tremendous work has been done to achieve feasible anode materials for SIBs and PIBs.

Among the various anode materials, hard carbon is the most promising anode material for SIBs due to its environmentally friendly, cheap, and productive properties. The capacity of hard carbon mainly comes from two mechanisms, the storage of ions between disordered graphene sheets and sodium ions filling the pores between the solid domains and undergoing adsorption on the surface. Based on these mechanisms, increasing interlayer space and improving the surface of hard carbon are important methods to improve the electrochemical performance of hard carbon. Doping the heteroatoms is an efficient way to raise sodium storage capacity, although a complex process is required. To avoid this issue, we use a simple low-temperature heating method to fabricate phosphorus-functionalized hard carbon with low specific surface area and low operating potential.

FoR codes (2008)

0912 MATERIALS ENGINEERING

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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.