Silicon-based anode materials for lithium-ion batteries Binghui Xu Bachelor of Engineering A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in 2015 School of Chemical Engineering Abstract While lithium-ion batteries (LIBs) have found wide applications in customer electronics, such as cellular phones and lap-top computers, the performance of the currently LIBs does not meet the market requirements for massive energy storage, such as electric vehicles and smart grids. One of the critical issues is the low energy capacity of the electrode materials. Graphite has been a common anode for LIBs, but the maximum capacity (372 mAh·g-1) of graphite has hindered its application in advanced LIBs. Substituting graphite with materials of high capacity has become an active research area. Graphene can store more Li+ than graphite because Li+ can not only be stored on both sides of graphene sheets, but also on the edges and covalent sites. Being electric conducting and mechanically strong, graphene is also an attractive support for other high capacity materials, such as silicon (Si). Si possesses the highest known theoretical capacity (4200 mAh·g-1, fully lithiated). However, Si suffers from a critical problem, namely severe volume change during charging/discharging, resulting in poor reversibility and rapid capacity decay. This PhD project aims to improve the stability and suitability of Si nanoparticles (SiNPs) for LIBs. The first aspect in this thesis is to demonstrate a novel approach to wrapping SiNPs in a reduced graphene oxide (RGO) aerogel framework. The aerogel-typed RGO architecture not only provided a porous network to accommodate the volume change of entrapping SiNPs, but also facilitated electrolyte transport and electron transfer. The second aspect in this thesis is to report a simple, green and scalable method to prepare RGO using gallic acid (GA) as a chemical reducing reagent. RGO samples reduced by GA showed a superior Li+ storage capacity compared with graphite and other reported graphene materials as anode for LIBs. The third aspect in this thesis is to report on the preparation of RGO-stabilized SiNPs, a sandwich-typed composite material (Si@RGO). As a result, good battery performance of Si@RGO was obtained, 1074 mAh·g-1 at the 5th cycle and 900 mAh·g-1 at the 100th cycle with a capacity retention of about 84% as well as excellent rate capability. I Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my research higher degree candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the policy and procedures of The University of Queensland, the thesis be made available for research and study in accordance with the Copyright Act 1968 unless a period of embargo has been approved by the Dean of the Graduate School. I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis. II Publications during candidature Journal Papers: 1. Graphene-based electrodes for electrochemical energy storage, Chaohe Xu, † Binghui Xu, † Yi Gu, † Zhigang Xiong, Jing Sun and X. S. Zhao, Energy and Environmental Science, 2013, 6, 1388-1414. († equally contributed first co-authors). 2. Stabilization of Silicon Nanoparticles in Graphene Aerogel Framework for Lithium Ion Storage, Binghui Xu, Hao Wu, C. X. (Cynthia) Lin, Bo Wang, Zhi Zhang, X. S. Zhao, RSC Advances, 2015, 5, 30624-30630. 3. Lithium-storage Properties of Reduced Graphene Oxide and its Silicon Based Composites, Binghui Xu, Jintao Zhang, Yi Gu, Zhi Zhang, Wael Al Abdulla, Nanjundan Ashok Kumar and X. S. Zhao*, Submitted to Scientific Reports. 2+ 4. Mesoporous carbon-coated LiFePO4 nanocrystals co-modified with graphene and Mg doping as superior cathode materials for lithium ion batteries, Bo Wang, Binghui Xu, Tiefeng Liu, Peng Liu, Chenfeng Guo, Shuo Wang, Qiuming Wang, Zhigang Xiong, Dianlong Wang and X. S. Zhao, Nanoscale, 2014, 6, 986-995. 5. Growth of LiFePO4 nanoplatelets with orientated (010) facets on graphene for fast lithium storage, Bo Wang, Shuo Wang, Peng Liu, Jie Deng, Binghui Xu, Tiefeng Liu, Dianlong Wang, X. S. Zhao, Materials Letters, 2014, 118, 137-141. 6. The synergy effect on Li storage of LiFePO4 with activated carbon modifications, Bo Wang, Qiuming Wang, Binghui Xu, Tiefeng Liu, Dianlong Wang and George Zhao, RSC Advances, 2013, 3, 20024-20033. Conference Proceedings: 1. Self-assembly of Graphene Silicon Nanoparticles into 3D Hierarchical Aerogel Nanocomposite for Lithium Ion Storage, Binghui Xu, Hao Wu, Zhigang Xiong, C. X. (Cynthia) Lin, Bo Wang, Peng Liu, and X. S. Zhao. Poster presentation at Asia-Pacific Conference On Electrochemical Energy Storage & Conversion (APEnergy 2014), 5–8 February 2014, Brisbane Convention & Exhibition Centre, Australia. III Publications included in this thesis 1. “Chaohe Xu†, Binghui Xu†, Yi Gu†, Zhigang Xiong, Jing Sun and X. S. Zhao*, Graphene-based Electrodes for Electrochemical Energy Storage, Energy and Environmental Science, 2013, 6, 1388-1414.” – incorporated as Chapter 2. Contributor Statement of contribution Co-first author Author Binghui Xu (Candidate) Wrote and edited paper (25%) Co-first author Author Dr Chaohe Xu Wrote and edited paper (25%) Co-first author Author Yi Gu Wrote and edited paper (25%) Author Dr Zhigang Xiong Wrote and edited paper (5%) Author Prof. Jing Sun Wrote and edited paper (5%) Author Prof. X. S. Zhao Wrote and edited paper (15%) 2. “Binghui Xu, Hao Wu, C. X. (Cynthia) Lin, Bo Wang, Zhi Zhang, X. S. Zhao*, Stabilization of Silicon Nanoparticles in Graphene Aerogel Framework for Lithium Ion Storage, RSC Advances, 2015, 5, 30624-30630.” – incorporated as Chapter 4. Contributor Statement of contribution Experimental design and performance (80%) Author Binghui Xu (Candidate) Wrote and edited paper (85%) Author Dr Hao Wu Experimental design and performance (20%) Author Dr C. X. (Cynthia) Lin Helped to run freeze drying process Author Bo Wang Helped to take EDS images Author Zhi Zhang Helped to take HR-TEM images Author Prof. X. S. Zhao Wrote and edited paper (15%) IV 3. “Binghui Xu, Jintao Zhang, Yi Gu, Zhi Zhang, Wael Al Abdulla, Nanjundan Ashok Kumar and X. S. Zhao*, Lithium-storage Properties of Reduced Graphene Oxide and its Silicon Based Composites, Submitted to Scientific Reports. – incorporated as Chapter 5 and Chapter 6. Contributor Statement of contribution Experimental design and performance (100%) Author Binghui Xu (Candidate) Wrote and edited paper (80%) Author Prof. Jintao Zhang Wrote and edited paper (5%) Author Yi Gu Helped to take FE-SEM images Author Zhi Zhang Helped to take HR-TEM images Author Dr Wael Al Abdulla Helped to record Raman spectroscopy Author Dr Nanjundan Ashok Kumar Wrote and edited paper (5%) Author Prof. X. S. Zhao Wrote and edited paper (15%) V Contributions by others to the thesis No contributions by others. Statement of parts of the thesis submitted to qualify for the award of another degree None VI Acknowledgements First of all, I would like to thank my parents for their sensible suggestions, directions and unselfish support in my study career. Then I would like to express my sincere gratitude to my respectable supervisors, Prof. X. S (George) Zhao and Prof. Lianzhou Wang for giving me guidance, encouragement and support throughout this work. Many thanks go to Prof. Joe Diniz da Costa and Prof. Chengzhong (Michael) Yu for being in my thesis committee, and for their constructive suggestions throughout my Ph. D candidature career. I am also grateful for the staffs in School of Chemical Engineering who helped to solve the financial as well as administrative issues. This project would not have been possible without the kind assistance from my dear colleagues in Prof. George Zhao’s research group. The facilities and technical assistance of the Australian Microscopy and Microanalysis Research Facility at the Centre for Microscopy and Microanalysis at the University of Queensland are acknowledged. I will take this opportunity to express my appreciation to the China Scholarship Council and the Australian Research Council for financial support over the PhD study. VII Keywords Lithium ion batteries, anode, stabilization, silicon nanoparticles, graphene, aerogel, composite Australian and New Zealand Standard Research Classifications (ANZSRC) ANZSRC code: 091205, Functional Materials, 60% ANZSRC code: 090406, Powder and Particle Technology, 20% ANZSRC code: 090403, Chemical Engineering Design, 20% Fields of Research