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Solid state and Materials Chemistry

Energy-related devices such as batteries and fuel cells are essential in our lives. In order to develop the next generation of technologies we need more power, or better performance, at a lower environmental cost. Research into understanding the interplay between the crystal structure of new materials and their physical properties will allow us to revolutionise how we obtain and store energy.

My research approach encompasses exploratory synthesis, structural determination, physical property measurements and in situ structure and property characterisation of batteries and other devices.

Towards the next generation of batteries: Sodium-ion batteries

Lithium-ion batteries are ubiquitous in our daily lives, e.g. mobile phones and laptop computers, but their limitations have restricted wide-scale use in applications requiring higher power, e.g. electric vehicles and energy storage of renewable energy. This project will target new battery chemistries, in particular sodium-ion batteries, by developing and characterizing new electrode and electrolyte materials. We will work to develop a reliable and affordable room-temperature sodium-ion battery to provide sufficient power for large-scale energy storage from intermittent renewable power sources. Students will work on one of the following parts of a battery and test their component in idealized batteries.

• Positive electrode materials

These electrodes provide the source of the sodium-ions and represent the largest cost and energy limitations for lithium-ion batteries. Here, new sodium-containing transition metal oxides, phosphates or sulfates are be synthesized and characterized to determine the relationship between crystal structure and battery performance.

• Electrolytes

Sodium-ion conducting ceramics or glassy-ceramics are known to be excellent electrolytes at high temperatures (>300°C). We work towards making materials with sufficient sodium-ion conduction at room temperature.

• Negative electrode materials

Negative electrodes are the least investigated component in a sodium-ion battery and the compounds used for lithium-ion batteries show poor performance in sodium-ion batteries. By developing new negative electrodes and understanding their limitations towards reversible sodium insertion/extraction we will be enable the next generation of devices. The focus of these projects are carbon based materials and the use of solid state ²³Na NMR to characterise the insertion/extraction processes.

Tuning negative thermal expansion to produce zero thermal expansion materials

The majority of materials expand during heating via thermal expansion and this process is responsible for billions of dollars per year in maintenance, re-manufacture and replacement costs due to wear and tear on both moving parts (e.g. in aircraft gas turbines), and components that are designed to be static (e.g. in optics, coatings, electronics). If a zero thermal expansion (ZTE) material can be made, a material that neither expands nor contracts upon heating, this could dramatically reduce industrial costs. In order to achieve this, the opposite extreme of materials are considered in this project - negative thermal expansion (NTE) is a property exhibited by a small group of materials predominantly due to transverse vibrations of atom groups or cooperative rotations of units (e.g. –CN- or WO₄). These materials typically feature large crystallographic voids and cations with variable oxidation states. So why not use a battery as a synthesis tool? In this project we will controllably insert Li and Na into the voids of the NTE materials, via a battery, in order to tune the cooperative rotations to produce ZTE materials.

In situ studies of materials

Investigating materials functioning in actual devices, i.e. in situ, allows the direct comparison of device performance to the atomic-level changes in the material. By manipulating the atomic-scale crystal structure of components, using a variety of synthetic techniques, improvements in device performance can be achieved, e.g. better lithium-ion batteries can be made.

Development of new ionic conductors

Full solid-state devices are more advantageous than liquid-containing devices as they are generally safer and more robust under harsh conditions however limitations arise particularly due to the lower ionic conductivity in solids. Exploring the mechanism of ionic conduction in solids, and its relationship to factors such as temperature and dopant concentration is a method to significantly improve solid-state devices.

Structural investigations using neutron and X-ray scattering

Single crystal, solid-state and electrochemical synthetic techniques can be used to tailor-make new materials for specific applications, but critical to this process is the characterisation tools employed to elucidate the arrangement of atoms. Our use of the Australian Synchrotron and the neutron scattering facilities at ANSTO provide unparalleled insight into these materials.

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