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Metal Sulfides and Their Lithium Storage Properties This document is downloaded from DR‑NTU (https://dr.ntu.edu.sg) Nanyang Technological University, Singapore. Metal sulfides and their lithium storage properties Liu, Weiling 2017 Liu, W. (2017). Metal sulfides and their lithium storage properties. Doctoral thesis, Nanyang Technological University, Singapore. http://hdl.handle.net/10356/69644 https://doi.org/10.32657/10356/69644 Downloaded on 11 Oct 2021 05:05:07 SGT METAL SULFIDES AND THEIR LITHIUM STORAGE PROPERTIES LIU WEILING SCHOOL OF MATERIALS SCIENCE AND ENGINEERING 2017 METAL SULFIDES AND THEIR LITHIUM STORAGE PROPERTIES LIU WEILING SCHOOL OF MATERIALS SCIENCE AND ENGINEERING A thesis submitted to the Nanyang Technological University in partial fulfilment of the requirement for the degree of Doctor of Philosophy 2017 Statement of Originality I hereby certify that the work embodied in this thesis is the result of original research and has not been submitted for a higher degree to any other University or Institution. 11 Aug 2016 . Date Liu Weiling Abstract Abstract Lithium ion battery (LIB) is currently one of the most widely used forms of rechargeable energy storage system in portable electronics. To achieve LIB with enhanced lithium storage properties, better safety aspects and lower cost, extensive research has been conducted on the various components of a LIB for the past few decades. Although graphite is currently used as the anode material in most commercial LIB, its limited capacity and the safety issues related to its low electrochemical potential ( vs. Li/Li +) have prompted scientists to search for alternative materials. Amongst the various conversion-typed materials, metal sulfides are particularly interesting as sulfur (S) has a rich and versatile chemistry, thus providing the possibility of altering the lithium storage properties of the materials by simply varying the stoichiometric ratio between the metal and sulfide ion in the compound. However, as with all sulfur and sulfide electrodes, polysulfides will be formed during their partial reduction, resulting in poor capacity retention and cycling performance in lithium and lithium ion batteries. In view of this, more study needs to be carried out to find approaches that can be undertaken to improve the lithium storage performance of metal sulfide electrodes. Hence, this thesis aims to gain an insight into how the amount of sulfide ion in the stoichiometry of a metal sulfide compound affects its lithium storage properties, with the focus placed on two metal sulfide systems, namely, iron sulfides (intercalation-conversion material) and tin sulfides (conversion-alloying material). To investigate the effect of how the amount of sulfide ion in the stoichiometry of an iron sulfide compound affects its lithium storage properties, pyrrhotite Fe 1-xS and pyrite FeS 2 with good purity have been successfully synthesized via a solution-based chemical synthesis method and their electrochemical properties were characterized. It was found that pyrite FeS 2 exhibits better lithium storage capability than pyrrhotite Fe 1-xS because of: (1) the lower polarization, better electron and Li + ion transport at the interface between the active material and electrolyte at the pyrite FeS 2 electrode and (2) the reversible lithiation and delithiation of iron sulfide (FeS y) during the galvanostatic cycling of the pyrite FeS 2 electrode. i Abstract SnS and SnS 2 with good purity have also been successfully prepared via a solution-based chemical synthesis method to investigate the effect of how the amount of sulfide ion in the stoichiometry of a tin sulfide compound affects its lithium storage properties and the electrochemical properties of these compounds were characterized. It was found that SnS 2 displayed a higher capacity and better cycling stability than SnS after prolonged cycling particularly at higher current densities. Since the SnS 2 electrode was found to have a poorer electronic and ionic conductivity than the SnS electrode, its superior lithium storage performance is attributed to its chemical and structural properties. As evidenced by the higher discharge capacity attained from the intercalation and conversion reaction throughout the 100 cycles, more Li 2S is formed during the lithiation of SnS 2, thus providing a thicker layer to buffer the large volume change during the lithiation and delithiation of Sn. This can result in a reduction in the pulverization and better capacity retention of the electrode after prolonged cycling, as verified by the slower alloying capacity fading rate observed in the SnS 2 electrode compared to the SnS electrode. It is found in this dissertation that for both iron and tin sulfides, the compound with a higher sulfide ion content in its stoichiometry i.e. FeS 2 and SnS 2 exhibits better lithium storage performance than its counterpart with lower sulfide ion content i.e. Fe 1-xS and SnS when cycled in a voltage window of 0.001 – 3 V. For the pyrite FeS 2 electrode, which undergoes intercalation and conversion reaction during cycling, the superior lithium storage performance is attributed to its better conductivity and reversibility of the lithiation and delithiation of FeS y. On the other hand, the SnS 2 electrode, which undergoes conversion and alloying reaction during cycling, displayed a better lithium storage performance due to its ability to form a thicker Li 2S layer which provides better buffering for the large volume change in the Sn particles during their alloying reaction, thus maintaining structural integrity of the electrode and result in slower capacity fading. ii Acknowledgements Acknowledgements The author would like to express her sincerest gratitude to her PhD supervisor, Associate Professor Hng Huey Hoon for her patient guidance for the past years. Thank you for always being there to provide valuable advices, help and inspiration, prompting me to think deeper but never ever limiting me from trying out new ideas. Research would have been a lonely journey without all my endearing labmates like Dr Tan Hui Teng, Dr Xu Chen, Dr Rui Xianhong and many more, in particular, “The Three Musketeers” – Dr Tan Li Ping and Dr Fan Shufen. The completion of this thesis would not be possible without your constant assistance and encouragement. You are all deeply loved and appreciated! To all the technical staffs in MSE especially Patrick, Wilson, Yee Yan, Dr Zvaid, Poh Tin and Swee Kuan, thank you for all the help and assistance rendered to me in one way or another throughout the pursue of my PhD. A big thank you also goes to the little “farm” in IMRE which includes Dr Lim Siew Lay, Ms Ivy Wong, Mr Goh Wei Peng, Dr Tan Mein Jin, Dr Ho Jian Wei and Dr Kam Zhiming for their support, be it technically, physically or emotionally. A balance needs to be strike between work and life. Thank you to my dearest friends – Hami, ZL, Xiuhui, Amanda and Poon for taking good care of my social life, listening to all my ranting when things are not going smoothly for me and for sharing my joy when I have things to be happy about. Last, but definitely not the least, the author would also like to express her deepest gratitude to her family. I know that some of the decisions that I had made can be quite wilful, but all these were done with the faith that you will always be there for me to fall back on if anything goes wrong. Thank you, Mummy, Daddy, my “stupid” Bro, Grandma and my beloved late Grandaunt for all the love and support! I am who I am because I have you around me. Carpe Diem – Seize the day, live your day to the fullest and make your life extraordinary! iii Acknowledgements iv Table of Contents Table of Contents Abstract ............................................................................................................................... i Acknowledgements .......................................................................................................... iii Table of Contents .............................................................................................................. v Table Captions .................................................................................................................. ix Figure Captions ................................................................................................................ xi List of Publications ......................................................................................................... xv Chapter 1 ........................................................................................................................... 1 1.1 Problem Statement .................................................................................................. 2 1.2 Motivation ............................................................................................................... 5 1.3 Research Scope and Objectives .............................................................................. 6 1.4 Thesis Flow and Organization .............................................................................. 10 1.5 Findings and Outcomes/Originality ...................................................................... 11 References: ........................................................................................................................ 12 Chapter 2 ......................................................................................................................... 17 2.1 History of Batteries ............................................................................................... 18 2.2
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