Future work

7.2.1 From the application perspective of as-dealloyed nanoporous metallic materials Sn-based and Cu-based porous materials have been created in this research which meets the requirements for applications in LIBs. Only a preliminary assessment of porous Sn in LIBs has been performed. Nanoporous Cu is expected to be far more outperforming than microporous Sn. However, its performance has not been assessed as yet, where the lack of sufficient mechanical integrity has been a critical issue to the as-dealloyed nanoporous Cu materials.

The low mechanical integrity of the nanoporous Cu materials developed arises from: (i) the mechanical defects (microcracks, voids, shrinkages) which exist in the precursor alloy foils prior to dealloying; (ii) the existence of undesired intermetallic phases (which are brittle in nature) in the precursor alloy, and (iii) the inappropriate selection of dealloying electrolytes or processes which lead to uncontrollable dissolution and diffusion in the precursor alloys and therefore resulted in inhomogeneous nanoporous structures. These challenges might be addressed through utilizing a novel metal foils production technology (as discussed below) and through incorporating innovative fundamental developments to the dealloying practice made so far.

The metal foils production technology suitable for this purpose must meet the following requirements:

 It is a rapid solidification process and can be used to produce Cu-based alloy foils with an ultrafine homogeneous microstructure. The finer the microstructure of the precursor alloy, the more homogeneous the resultant nanoporous structure will be.

Accordingly, a precursor alloy with an ultrafine or even a nanometric microstructure is always preferred.

 It can be used to produce Cu-based precursor alloy foils with different thicknesses and widths by varying the nozzle design and controlling melt flow and solidification rates.

These characteristics can avoid the subsequent machining process such as cutting or polishing, which often introduces extra stress or contamination to the foil products.

 It is easy to change the superheat of the alloy melt and the solidification rate to achieve the optimization of the microstructure of the precursor alloys.

 It can realize large volume production for the production of the large scale of functional nanoporous Cu required in applications, e.g. up to several hundred meters per minute.

Following the improvement of mechanical integrity of the precursor alloy and the as-dealloyed products, systematic LIB studies of nanoporous Cu-Sn composites by tailoring experimental conditions is necessary. The exploration of the application of nanoporous Cu in heat and electrical transferring should be considered as well.

7.2.2 From the perspective of further understanding the dealloying process

In Chapter 6 of this thesis, a number of new experimental findings have been derived from the ex-situ and in-situ synchrotron studies of a variety of Al-Cu and Al-Cu-Sn alloys. Based on the preliminary analysis of those experimental findings, we made certain understandings, such as the critical role of crystal structure evolution in creating hierarchical porous structures, and in revisiting the parting limit of Al-Cu alloy system, and the identification of formation of Cu3Sn by the consumption of Cu6Sn5 and Cu. Our future studies will deal with:

1) Further systematic analyses (e.g. Rietveld Refinement analysis of each dataset) will be made of the ex-situ/in-situ synchrotron powder diffraction data.

2) Corresponding characterizations by other means, like SEM, TEM etc., of certain samples will be done to provide supplementary evidence for comprehensive understanding. In addition, the surface area measurements (such as BET and BJH) will be carried out as well, for robust results including surface area, porosity and pore distribution of the as-dealloyed porous materials.

It can lead to a more systematic understanding of not only dealloying of the Cu and Al-Cu-Sn alloy systems, but also of other binary and/or ternary alloys. It can provide the improved fundamental basis for the design and creation of advanced metallic materials via dealloying for wider industrial applications.

Acknowledgments

I would like to acknowledge my principle supervisor, Prof Ma Qian. The value of his advice, unique and creative ideas and generous financial support is beyond quantification. I particularly want to appreciate Ma for training me to think critically and logically.

My co-supervisor Assoc Prof Ming Yan, deserves considerable credit for the initial offer, the constructive discussions and considerate encouragement all the time. I still don’t know where his humility comes from and I do own him a lot of gratitude.

To my co-supervisor Prof Andrej Atrens, appreciate his generous support on the access of electrochemistry workstation and knowledge of electrochemistry.

Great thanks go to the financial support from China Scholarship Council (CSC) Scholarship, the University of Queensland International (UQI) Scholarship, Graduate School International Travel Award (GSITA) of UQ, RMIT Tuition Fee Wavier and Higher Degree by Research Travel Grant (HDRTG) of RMIT University.

Appreciate both of Centre for Microscope and Microanalysis (CMM) in UQ and RMIT Microscope and Microanalysis Facility (RMMF) for the facilities and scientific and technical assistance. Synchrotron XRD experiments were performed at the Australian Synchrotron Powder Diffraction Beamline (PD/8856, PD/7953, PD/7552).

I would like to thank the following people:

Dr Justin Kimpton of Australian Synchrotron for his generous advice on synchrotron beamline proposal submission, in-situ synchrotron experimental setting up, data analysis;

Dr Nathan Webster of CSIRO Mineral Resources Flagship, for his support on synchrotron experimental setting up, guidance on the refinement analysis by TOPAS;

Dr Mark styles of CSIRO Manufacturing Flagship, for his assistance on the synchrotron experimental setting up and overnight stay for the synchrotron experiments;

Prof Qijie Zhai and Prof Yulai Gao from the Center of Advanced Solidification Technology, Shanghai University, China for the access of the devices of melt-spinning and suction casting.

Dr Zhiming Shi of The University of Queensland for great help he offered related to the access of electrochemistry work station and analysis of electrochemical results;

Prof Yungui Chen of Sichuan University, China, for offering me an opportunity to stay in his group for two months, during which I started to know more about materials used in a battery and the entire battery field as well.

Colleagues in the University of Queensland and RMIT University. I’m so lucky that I could do the PhD in two places and I’m so grateful for your listening, sharing and companying.

Prof Frank Uwe Renner from Hasselt University, Belgium and A/Prof Takeshi Fujita from Tohoku University, Japan, the two examiners of this thesis, for their time, and positive and in-depth comments and suggestions.

I would like to thank my father back in China for his unconditional love and understanding.

Finally to my mother: I have been firmly believing that you would be the happiest, the proudest one in the world if you knew your girl entered the university, did a master and now is finishing a PhD.