The synthesis and application of energy storage materials derived from small molecules

.. .THE SYNTHESIS AND APPLICATION OF ENERGY STORAGE MATERIALS DERIVED FROM SMALL MOLECULES ZOU SHIQIANG (M.Sc, Peking University) A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF SCIENCE... this thesis, lab-scale synthesis and preparations are conducted to obtain organic and inorganic materials, which are polycarbazole and Sb-carbon composite, both derived from small molecules for energy- related... attention to energy and environmental issues Scientists from all over the world try their best to enhance the electrochemical performance of current energy storage techniques and explore new energy

THE SYNTHESIS AND APPLICATION OF ENERGY STORAGE MATERIALS DERIVED FROM SMALL MOLECULES ZOU SHIQIANG NATIONAL UNIVERSITY OF SINGAPORE 2014 THE SYNTHESIS AND APPLICATION OF ENERGY STORAGE MATERIALS DERIVED FROM SMALL MOLECULES ZOU SHIQIANG (M.Sc, Peking University) A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF SCIENCE DEPARTMENT OF CHEMISTRY NATIONAL UNIVERSITY OF SINGAPORE 2014 Declaration I hereby declare that this thesis is my original work and entirety, under the supervision it of Prof. Loh Kian Ping has been written by me in its (Graphene Research Center), Department of Chemistry National University of Singapore, between August, 2013 and July, 20t4. I have duly acknowledged all the sources of information which have been used in the thesis. This thesis has also not been submitted for any degree in any university previously. Zou Shiqian Name s Ztu Cryry Signature An.>t * , Date ?atV Acknowledgements I would like to dedicate this dissertation to my supervisor Prof. Loh Kian Ping, who has offered me lots of guidance and support during my study and research period in NUS. Besides, I’m also deeply inspired by Prof. Loh’s enthusiasm in exploring cutting-edge scientific issues. That is the most important virtue that a true and ingenious scientist should be equipped with. Secondly, I owe a large part of my progress to Dr. Su Chenliang and Dr. Peng Chengxin. My horizon is broadened by working together with these two brilliant brains. Their guidance and support are highly appreciated as well. They should be regarded as my role model if I want to devote myself to scientific research. Besides, I want to give my special thanks to Su Jie, who has given me tremendous help in this lab as a classmate and partner. All those time we spent at the GRC and fighting for success will surely be precious memory to me. This young man’s devoted heart and logical mind influence me a lot during our experiment time. Sincere thanks to all the staff and all the members of our research group, especially Ms. Rika, the warm-hearted research assistant, and Ms. Meng Xing. Not only do they offer important assistance, but make my life in NUS more colorful and fruitful. II Finally, I should tribute to all the professors and staff of the SPORE committee. With your unselfish and industrious effort, I can have this valuable chance to study in NUS and explore Singapore. Indeed, I benefit hugely from this SPORE dual master program. III Table of Contents PAGE DECLARATION ................................................................................................................... I ACKNOWLEDGEMENTS ................................................................................................II TABLE OF CONTENTS .................................................................................................. IV SUMMARY ........................................................................................................................ VII LIST OF TABLES.............................................................................................................. IX LIST OF FIGURES ............................................................................................................ X PAGE CHAPTER 1: LITERATURE REVIEW ........................................................................ 1 1.1 Fundamentals of Li-ion battery system ........................................................................... 1 1.2 Developments of anode materials in battery system ...................................................... 4 1.3 Inorganic anode materials ................................................................................................ 5 1.4 Organic anode materials ................................................................................................... 7 1.5 Objectives and scope of the dissertation .......................................................................... 9 IV CHAPTER 2: ORGANIC ANODE MATERIAL DERIVED FROM SMALL ORGANIC MOLECULAR FOR LI-ION BATTERY .............................................. 11 2.1 Background ...................................................................................................................... 11 2.2 Experiment scheme and approaches ............................................................................. 12 2.3 Results and discussion ..................................................................................................... 14 2.3.1 Synthetic approaches of PTCB...................................................................................14 2.3.2 Characterization of TCB and PTCB...........................................................................14 2.3.3 Electrochemical performance of TCB and PTCB .......................................................18 2.4 Extended application of PTCB in photocatalysis area ................................................. 25 2.4.1 Fundamentals of photocatalysis .................................................................................25 2.4.2 Principles of PTCB as a photocatalyst .......................................................................26 2.4.3 Experiment procedure of photocatalysis ....................................................................27 2.4.4 Photocatalysis performance of PTCB ........................................................................28 2.5 Conclusion and future work ........................................................................................... 30 2.5.1 Main conclusion ........................................................................................................30 2.5.2 Future work ..............................................................................................................32 CHAPTER 3: INORGANIC ANODE MATERIAL DERIVED FROM SMALL ORGANIC MOLECULES FOR NA-ION BATTERY.............................................. 33 3.1 Background ...................................................................................................................... 33 3.2 Experiment scheme and approaches ............................................................................. 34 3.3 Results and Discussion .................................................................................................... 35 V 3.3.1 Preparation of nano Sb-carbon composite .................................................................35 3.3.2 Characterization of nano Sb-carbon composite ..........................................................36 3.3.3 Electrochemical performance of Sb-carbon composite ...............................................40 3.4 Conclusion and future work ........................................................................................... 43 3.4.1 Main conclusion ........................................................................................................43 3.4.2 Future work ..............................................................................................................44 CHAPTER 4: SUPPORTING INFORMATION ........................................................ 45 4.1 Reagents information ...................................................................................................... 45 4.2 Equipment information................................................................................................... 47 CHAPTER 5: REFERENCES ......................................................................................... 48 VI Summary Nowadays, people are paying increasing attention to energy and environmental issues. Developing materials, which can be used in energy-related fields, are commonly recognized as one of the most important human endeavors for sustaining growth. In order to shine some light on potential approaches to energy-related issues, several kinds of organic and inorganic materials, primarily derived from small molecules, were successfully synthesized in this study and systematically investigated in energy-related application: Li-ion battery, Na-ion battery and photocatalysis. The results obtained indicates that the small organic molecule, 1,3,5-tri(9H-carbazol-9yl)benzene (TCB), is highly promising as a candidate material to be deployed as anode in the lithium battery system. With high initial specific capacity (800-900 mAh/g), relatively stable rate and cycling performance and nearly 100 % coulomb efficiency, the novel small organic molecule, TCB, is a suitable anode material in Li-ion battery system. The organic polymer, micro-wire polycarbazole (PTCB), which is primarily derived from TCB, also presents some electrochemical features with relatively low specific capacity and cycling stability. However, PTCB’s performance as a photocatalyst is outstanding. By using acetonitrile as the solvent and providing adequate oxygen, the conversion rate and selectivity achieve 100 % and 98 %, respectively, after 2 hours’ visible-light exposing. Obviously, PTCB shows a bright future as an effective photocatalyst in photochemical synthesis. Thus, both the VII TCB and PTCB, as novel organic materials, would contribute much to energy-related applications. The novel inorganic Sb-carbon composite, which is derived from small organic molecule (triphenylstibane), presents excellent electrochemical performance as the anode material in the sodium-ion battery system. Containing carbon (52 %) and antimony (35 %), this material exhibits large specific capacities (800 mAh/g @ 1C, 630 mAh/g @ 2C and 580 mAh/g @ 4C). Besides, it displays rather stable performance and high (>99%) coulombic efficiency under different rates. Thus, this material is highly promising for application in sodium-ion battery. VIII List of Tables PAGE TABLES Table 1.1 Theoretical gravimetric and volumetric specific capacities of 6 Li-alloying elements Table 3.1 Elemental analysis of Sb-carbon composite at different 40 temperatures Table 4.1 All the reagents used in this study 45 Table 4.2 All the equipment used in this study 47 IX List of Figures FIGURES Fig. 1.1 PAGE Illustration of the charge/discharge processes in rechargeable 2 Li-ion battery Fig. 1.2 The redox mechanisms of three types of organic materials 8 Fig. 1.3 Typical inorganic/organic electrode materials and their 8 corresponding redox voltage and specific capacity for rechargeable lithium batteries Fig. 2.1 Novel organic polymers containing conjugated amine 11 structure and their theoretical specific capacity Fig. 2.2 The schematic of the main chemical reaction in PTCB 12 synthesis Fig. 2.3 The experiment scheme of chapter 2 13 Fig. 2.4 TGA result of TCB 15 Fig. 2.5 TGA result of PTCB 15 Fig. 2.6 FTIR spectrum of TCB and PTCB 16 Fig. 2.7 SEM image of PTCB 17 Fig. 2.8 UV absorbance spectrum of TCB and PTCB 17 Fig. 2.9 Cyclic voltammogram (CV) curve of TCB 20 Fig. 2.10 Cycling performance of TCB 20 Fig. 2.11 Charge-discharge curve of TCB 21 Fig. 2.12 Rate performance of TCB at different rates 22 Fig. 2.13 Cyclic voltammogram (CV) curve of PTCB 23 Fig. 2.14 Cycling performance of PTCB 24 Fig. 2.15 Charge-discharge curve of PTCB 25 Fig. 2.16 The schematic diagram of PTCB-based photocatalysis 27 X Fig. 2.17 The schematic diagram of photocatalysis when PTCB worked 28 as the catalyst and benzylamine worked as electron donor Fig. 2.18 Photocatalysis reaction when benzylamine served as electron 28 donor Fig. 2.19 The conversion rate and selectivity of PTCB, graphene-C3N4 30 and TiO2 for photocatalysis experiment Fig. 3.1 The experiment scheme of chapter 3 35 Fig. 3.2 The macro-surface structure of the Sb-carbon composite 36 Fig. 3.3 Transmission electron microscopy (TEM) picture of the Sb- 37 carbon composite (side view) Fig. 3.4 TEM picture of the Sb-carbon composite (top view) 37 Fig. 3.5 The spherical structure of Sb-carbon composite (low 38 magnification) Fig. 3.6 The spherical structure of Sb-carbon composite (high 38 magnification) Fig. 3.7 X-ray diffraction (XRD) of Sb-carbon composite 39 Fig. 3.8 Raman spectrum of Sb-carbon composite 39 Fig. 3.9 CV curve of Sb-carbon composite 42 Fig. 3.10 The specific capacity and coulombic efficiency of Sb-carbon 42 composite in Na-ion battery Fig. 4.1 The 1H NMR spectrum of TCB (CDCl3, 300 Hz) 46 Fig. 4.2 The 13C NMR spectrum of TCB (CDCl3, 300 Hz) 46 XI Chapter 1: Literature Review Nowadays, people are paying increasing attention to energy and environmental issues. Scientists from all over the world try their best to enhance the electrochemical performance of current energy storage techniques and explore new energy sources as well as energy-related materials with outstanding performance [1, 2]. Efficient and portable energy storage equipment and devices hold the key to the future development of human society. The electrode is an essential part of the battery system and is absolutely vital in the improving current energy conversion efficiency of batteries. Due to the deterioration of current environment and increasing awareness of protecting earth, attentions are now focused on not only the electrochemical performance of certain electrode material, but also the safety issues, cost-effectiveness and environmental friendliness [3]. 1.1 Fundamentals of Li-ion battery system The first Li-ion graphite electrode was manufactured in Bell Labs. The Li-ion battery was later commercialized by Sony Company in 1991. In this battery, exchanging of Li+ is realized between graphite (LixC6) anode and a layered-oxide (Li1-xTMO2). TM stands for transitional metal, such as cobalt, nickel, manganese, etc [4]. Li-ion battery, like all the other batteries, consists of two electrodes: cathode and anode. These two electrodes are connected by electrolyte. Different chemical reactions happen on 1 these two electrodes. Once connected by external devices, electrons will flow from the negative-potential electrode to positive-potential electrode. In order to balance the charge, the ions inside the electrolyte will move accordingly. On the other hand, a larger voltage is required in the opposite direction to force the battery into the recharge phase [2]. Typically, following reactions (Fig. 1.1) occur in the Li-ion battery (LiCoO2 as cathode and LixC6 as anode): Charge   Li1-x CoO2 +Li + +xeCathode: LiCoO2   (1-1) Charge   Li x C6 Anode: 6C+xLi + +xe-   (1-2) Charge   Li1-x CoO2  Li x C6 Overall reaction: LiCoO2   (1-3) Discharge Discharge Discharge Fig. 1.1 Illustration of the charge/discharge processes in rechargeable Li-ion battery Currently, inorganic and organic electrode materials are both used in battery systems. Inorganic electrode materials have been thoroughly studied for decades and are widely 2 implemented in practical devices and commonly used in our daily lives. For example, LiCoO2, LiNiO2, LiMn2O4, LiNi1/3Co1/3Mn1/3O2 and LiFePO4 are usually used as the inorganic cathode materials in lithium system. All inorganic materials mentioned above exhibit a theoretical specific capacity less than 300 mAh/g and a practical specific capacity below 170 mAh/g. One drawback is that inorganic transition metal-containing electrode consumes elements that are not earth abundant and leads to corresponding environmental concerns with its use and disposal [5]. As for organic electrode material, more investigations are needed in the laboratory scale to design novel electro-active organic molecules and stabilize their performances. Actually, lithium organic battery can be traced back to 1969 [6], which is close to the time when lithium battery was invented [7]. In order to compete with inorganic electrode, scientists have tried endeavored to design different organic structures and redox mechanisms to achieve a higher performance for a prolonged time. For cathode materials, during the 1980-2000, conducting polymers and organodisulfides were popular organic electrode for Li-ion battery, even though their electrochemical performances are barely satisfactory [8]. After entering the 21st century, the focus was shifted to nitroxyl radical polymers and conjugated carbonyl compounds [9]. As for the anode materials, a few recent reports were focused on carbonyl-based organics [10, 11], dilithium rhodizonate and oxocarbons [5]. Recently, two organic salts, Li2C8H4O4 and Li2C6H4O4 were reported as the organic anode materials with redox potential at 0.8-1.4 V [12] 3 with a reversible capacities of 300 and 150 mAh/g, respectively. Although the energy density, cycling performance, stability and rate performance of certain organic electrode may be superior to those of previous inorganic ones, a huge gap still exists between laboratory scale investigation and massive industrial production. 1.2 Developments of anode materials in battery system Typically, anode materials in the battery system can be divided into three groups regarding their energy storage mechanisms: insertion type, conversion type and alloying-based type. Most commercially applicable anodes are insertion type. They are usually made up of transition metal oxides and graphite, which present excellent mechanical and electrochemical stability. However, the relatively lower theoretical specific capacity of transition metal oxides and the limited electrolyte choices partially hinder their further development. In the conversion-reaction type materials, the transitional metals in the compound can be replaced by Li [13-15]. For example, MnO will be reduced to Mn when lithiation happens, which oxides the Li to LixO. However, the theoretical specific capacity and the Li-ion mobility are relatively low. Moreover, larger polarization and voltage window for lithiation/delithiation will eventually reduce the energy density [16]. As for the alloying-based type anodes, they usually alloy with Li under electrochemical reactions. This type of anodes possesses higher charge capacity. The drawbacks are relatively low Li-mobility inside the alloy, low rate capability and limited cycle life [16]. 4 1.3 Inorganic anode materials The inorganic anode materials mainly discussed here are from the alloying-based type. All the Li-alloying elements’ theoretical and gravimetric specific capacities are shown in Table 1.1 [16]. As can be seen from this table, there are a wide selection of metal elements can be used as the anode material with different specific capacities and price. In order to choose the most suitable anode material, a series of factors need to be considered: high theoretical capacity, easy availability, high conductivity, relatively low environmental impact and most importantly low cost. Si has been thoroughly studied as anode for years due to its large theoretical capacity [17-19], with a maximum theoretical specific capacity of 3579 mAh/g [20, 21]. Si anode has also been studied extensively regarding its strengths and drawbacks. Recent studies on Si anode focused on fabricating nanostructure, such as Si nanoparticles [22-26] and porous nanowires [27]. Some of these anodes even achieve stable performance over 1000 cycles [28-30]. In addition, carbon-silicon composites, such as graphite-Si layers [31], C-coated Si nanoparticles [32], porous Si-C spheres [33], all achieve excellent performances. 5 Table 1.1 Theoretical gravimetric and volumetric specific capacities of Li-alloying elements Atomic Number 6 C Gravimetric Specific Capacity a 372 Volumetric Specific Capacity b 756 Price in the past 5 years c - 13 Al 993 1383 0.5-1.5 14 Si 3579 2190 0.7-1.2 15 P 2596 2266 - 30 Zn 410 1511 0.5-1 31 Ga 769 1911 100 32 Ge 1384 2180 500 33 As 1073 2057 1 47 Ag 248 1368 200-500 48 Cd 238 1159 1 49 In 1012 1980 150-350 50 Sn 960 1991 5-15 51 Sb 660 1889 3-7 79 Au 510 2105 10k-30k 82 Pb 550 1906 0.5-1 83 Bi 385 1746 8-12 Element a The unit of gravimetric specific capacity is mAh/g. b The unit of volumetric specific capacity is mAh/cm3. c The unit of price is USD/lb. Though it is much more expensive (according to Table 1.1), Ge has become increasingly popular because of its excellent conductivity and lithium diffusivity as compared to Si. Recently, the 500 nm Ge particles [34], 200 nm Ge sheets @ graphene [35] and 3-100 nm nano-Ge [36-41] were all tested in the lab-scale systems with stable cycling and rate capability. Instead of its elemental form, SnO has drawn more attention from scientists. Although its gravimetric specific capacity is lower than Si, the volumetric capacity of Sn is claose to the 6 latter one, Si. Nonetheless, the elemental form of Sn cannot achieve a stable cycling performance [42], whereas Sn oxides can present a high capacity of 1000-1400 mAh/g [43]. However, Sn can also be used as anode in the form of Sn/Co/C, which is commercialized by Sony Company and presents excellent cycle performance. Lastly, Sb has always been considered as a potential anode candidate because of its high theoretical capacity (660 mAh/g) and relatively low cost. Therefore, scientists are investigating various kinds of Sb anodes, such as Sb nanocomposites [44-47], bulk microcrystalline powders [48], Sb films [49]. Similar to carbon, Sb can display impressive electrochemical performances as well, such as Sb/C fibers [50], Sb/C nanocomposites [51], Sb/C nanotubes [52] and Sb/C thin films [49]. As a promising anode, Sb definitely can make great progress as a novel alloying-type (fully lithiation form as Li3Sb) material. 1.4 Organic anode materials Organic electrode materials are less popular in practical application largely due to their apparently poor electrochemical performance and specific capacity. However, owing to deeper understanding of the mechanism and continual improvement in the design of novel organic molecules, some lab-scale organic materials seem promising and may have bright future in industrial applications. 7 All organic electrodes can be divided into three groups, namely: p-type organics, n-type organics and bipolar organics. The redox mechanisms of all three groups of organics are shown in Fig. 1.2. Fig. 1.2 The redox mechanisms of three types of organic materials: (a) n-type; (b) p-type; (c) bipolar (derived from reference [53]) Fig. 1.3 shows some typical inorganic/organic electrode materials and redox voltage and specific capacity for rechargeable lithium batteries. Because most of the redox potentials for organics ranged from 2.0 to 4.0 V, they are more likely to be applied as cathode than anode. Fig. 1.3 Typical inorganic/organic electrode materials and their corresponding redox voltage and specific capacity for rechargeable lithium batteries (derived from reference [53]) 8 Few organic anode materials are reported, including bipolar types [54, 55] and conjugated dicarboxylates [12, 56-59]. For small organic molecules, many can achieve satisfying discharge capacity and energy density. However, all small molecules substances are confronted with the dissolution problem and poor cycling performance. Compared to monomers, organic polymers are insoluble in most of the electrolyte. Thus, some scientists try to solve the dissolution problem by polymerization. The polymers, unfortunately, have other drawbacks, such as reduced theoretical specific capacity, enlarged electrochemical polarization and lower ion mobility. However, there is no denial that organic anodes, regardless of small molecules or polymers, possess a myriad of advantages over conventional inorganic ones: higher energy and power density, structure diversity (by design), flexibility (more methods to fabricate with different morphology at the molecular level), sustainability (more accessible and no use of transitional metals), cheap and better dissolution condition (especially for organic polymers). 1.5 Objectives and scope of the dissertation High-performance and environmental friendly materials in the energy-related applications are critically needed to fulfill the increasing energy demand in our modern society. However, few studies are targeted on organic Li-ion anode material and inorganic Na-ion anode material derived from small molecules. In this thesis, lab-scale synthesis and preparations are conducted to obtain organic and inorganic materials, which are polycarbazole and Sb-carbon 9 composite, both derived from small molecules for energy-related applications. Thorough characterizations together with investigations regarding electrochemical performance are studied in lithium-ion and sodium-ion battery systems. In addtion, extended application of PTCB as potential photocatalyst is explored to determine whether it can be utilized as a multifunctional material. The specific goals of this thesis are: 1. Upon obtaining the organic monomer, 1,3,5-tri(9H-carbazol-9-yl)benzene (TCB), novel polycarbazole material (PTCB) containing amine moieties is successfully synthesized and thoroughly characterized. Both the electrochemical performances of organic monomer and polymer are tested in the lithium-ion battery systems as the anode. 2. PTCB’s photocatalytic potential is investigated and systematically optimized. The possibility of polycarbazole serving as multifunctional material is scrutinized as well. 3. Inorganic Sb-carbon composite derived from small organic molecules is investigated for its electrochemical performance in sodium-ion battery system. The cycling behavior, rate capability, specific capacity and charge-discharge performance of this inorganic material are thoroughly studied. 10 Chapter 2: Organic anode material derived from small organic molecular for Li-ion battery This chapter was targeted at synthesizing a novel organic polymer, which is derived from a small organic monomer, 1,3,5-tri(9H-carbazol-9-yl)benzene (TCB). Further investigation regarding the small molecule (TCB) and its polymer’s electrochemical performance was conducted to explore their potentials in practical lithium-ion battery systems. The PTCB’s performance as a photocatalyst was further evaluated. 2.1 Background The conjugated amine structure has already been investigated extensively as cathode material in the previous studies [60-63]. Recently, two new types of conjugated amine were reported, which are shown in Fig. 2.1. Fig. 2.1 Novel organic polymers containing conjugated amine structure and their theoretical specfic capacity: polytriphenylamine (PTPAn) and poly(N-vinylcarbazole) (PVK). 11 Both of them are categorized as n-type organic materials and thus are applied as the cathode material in battery systems. Although the PTPAn presents low theoretical specific capacity, its rate capability and cycling performance are excellent [64]. As for PVK, the specific capacity is a little bit higher than PTPAn when applied as the cathode material [65]. Though no previous studies have ever been done, we hypothesized that conjugated amine together with benzene ring might possess the possibility to receive electron and served as the anode. 2.2 Experiment scheme and approaches The small organic molecule, 1,3,5-tri(9H-carbazol-9-yl)benzene (TCB), was commercially available from Sigma Aldrich (Singapore). The polymer, poly-TCB (PTCB) was further synthesized through a modified method of the one used by Chen [66] (Fig. 2.2). N N N N N N FeCl3, CH3Cl N N N R. T. N N N Fig. 2.2 The schematic of the main chemical reaction in PTCB synthesis Upon the acquirement of both TCB and PTCB, a series of characterizations were applied to determine the substance, investigate the microstructure and other features. The scheme is shown in Fig. 2.3. The Ultra-shield 300 Hz nuclear magnetic resonance (NMR) spectrometer 12 (Brucker, Germany) was first used to determine TCB. Both 1H NMR and 13 C NMR were conducted by using the CDCl3 as the solvent. All the data was processed by the software to get a clear identification of the compound. Thermal gravity analysis (TGA) was then conducted to compare the difference of thermostability of both TCB and PTCB under N2 protection. The initial temperature was the room temperature (about 28 ℃). The heating speed was 10 ℃ per minute until it reached 1000 ℃. UV-VIS absorption spectrometry and Fourier Transform Infrared Spectroscopy (FTIR) were applied for further characterization. Finally, the small molecule, TCB, and its polymer, PTCB, were both tested for their electrochemical performances. Since the polymer exhibits interesting photophysical properties, its use as a photocatalyst was thoroughly explored. SEM Characterization of TCB and PTCB TGA UV-VIS FTIR Synthesis of poly- Electrochemical TCB from TCB performance as TCB’s feature anode materials PTCB’s feature Photocatalysis Conversion rate experiment for PTCB Fig. 2.3 The experiment scheme of chapter 2 13 Selectivity 2.3 Results and discussion 2.3.1 Synthetic approaches of PTCB The synthesis of PTCB was carried out using a modified method as reported in literature[66]. TCB (200 mg, 0.37 mmol) was dissolved in 30 mL anhydrous chloroform. The dissolved solution was injected into 250 mL flask through a 20 mL syringe, which was charged with ferric chloride (0.5 g, 3.08 mmol). Another 30 mL anhydrous chloroform was added into the system through the same approach. The solution was stirred at room temperature for 1 day under nitrogen protection. 100 mL methanol was then added to the above reaction mixture. The resulting mixture was stirred for another hour. The precipitate was collected by filtration. All the solids obtained were washed with 250 mL methanol and then stirred vigorously in 250 mL two-neck flask with 150 mL HCl (37%). After 2 hours, the suspension was filtered and thoroughly washed with DI water and methanol. All the obtained solids were further purified through Soxhlet extraction with methanol at 93 ℃ (24 hours) and with THF at 90 ℃ (24 hours). The desired polymer was collected and dried in vacuum oven at 80 ℃ overnight. In the end, 190 mg PTCB was collected. The final yield is 95 %. 2.3.2 Characterization of TCB and PTCB In order to compare the difference in thermostability between TCB and PTCB, both materials were tested for TGA. The TGA result of TCB is shown in Fig. 2.4. As for PTCB, 7.331 mg PTCB was used to determine its thermostability. The result is shown in Fig. 2.5. 14 Fig. 2.4 TGA result of TCB (the initial mass was 10.012 mg) Fig. 2.5 TGA result of PTCB (the initial mass was 7.331 mg) As can be seen in Fig. 2.4 and 2.5, the thermostability of TCB dramatically decreases from 350 ℃ to 470 ℃. However, PTCB remains at a stable mass when the temperature is below 15 500 ℃. These changes may result from the molecular structure difference after the polymerization, chemical bonds for instance. From the difference in the thermostability, it can be clearly seen that TCB should be chemically converted to PTCB, providing evidence for the successful polymerization reaction. Transmittance TCB 4000 PTCB 3500 3000 2500 2000 1500 1000 500 -1 Wavenumbers (cm ) Fig. 2.6 FTIR spectrum of TCB and PTCB Further FTIR experiment was conducted to investigate the infrared transmittance of the product. As can be seen in Fig 2.6, the main absorptions of infrared light for TCB and PTCB occur between the wavenumber of 1000-1700 cm-1. According to the spectra, the characteristic peaks of PTCB matches to that of TCB’s, although the peak intensities between 1200 and 1300 cm-1 have some changes. These similarities in the FTIR provide evidence towards the existence of similar functional groups in poly-TCB. 16 Fig. 2.7 SEM image of PTCB Fig. 2.8 UV absorbance spectrum of TCB and PTCB Considering a complete exploration of PTCB’s surface structure, SEM was applied in the following experiment. The SEM image is shown in Fig. 2.7. As can be seen, the micro-wire structure of PTCB is clearly observed. This microstructure certainly improves the mobility of Li-ion inside and thus will boost its electrochemical performance. 17 The UV absorbance of TCB and PTCB is displayed in Fig. 2.8. As can be seen, obvious differences can be observed from wavelength of 200 to 400 nm. The notable absorbance of PTCB in this region indicates that it may have some visible-range photochemical applications. 2.3.3 Electrochemical performance of TCB and PTCB A series of lithium battery experiments are conducted by using TCB and PTCB as the anode materials. The TCB and PTCB were first completely dried in the oven and then ground into fine particles together with super-P. Afterwards, all the materials were placed inside a small glass bottle. After adding a few drops of polyvinylidene fluoride (PVDF) solution (11%), the bottle was placed on magnetic stirrer. During the binding process, N-methyl-2-pyrrolodone (NMP, HPLC grade) was gradually added until particles and binder were mixed thoroughly. The rotate speed was 500-700 rpm. This process lasted c.a. 18 hours. All the materials inside the bottle would achieve a black semi-liquid state. Then, the mixture was placed on the copper sheet and coated on it by using a spreader (75 micrometer width). The coated copper sheet was put inside the vacuum oven at 80 ℃ overnight to remove the remaining NMP. Afterwards, the coated copper sheet was compressed with a roller and cut into small disks. These disks together with shells of button battery and spacers were once again placed inside the vacuum oven overnight. After heating for at least 8 hours inside the vacuum oven, the disks, shells of button battery and spacers were taken out and transferred into the glove box. All the assembly procedures 18 were conducted inside the glove box, where the concentrations of both oxygen and water were lower than 0.5 ppm. After the assembly process, the lithium batteries were taken out from the glove box and stabilized for at least 18 hours. All the well-functioning lithium batteries were tested for the cyclic voltammogram, chargedischarge performance and rating capabilities at different rates. In this experiment, LAND battery test system (Wuhan, China) was used to document the electrochemical performance of both TCB and PTCB as the anode material in the Li-ion battery. All the data were collected and further processed by using the Origin 8.0 software. 2.3.2.1 TCB’s electrochemical performance as anode material in Li-ion battery Six cycles of cyclic voltammogram (CV) are shown in Fig. 2.9. The scan voltage ranges from 0.01 V to 3.0 V. The oxidation-reduction potential of amine, according to the CV curve, appears at 0.8-1.0 V. From the second to the sixth cycle, the oxidation peak and reduction peak coincide with each other. The positions of oxidation and reduction peaks stay the same. Thus, the TCB material inside the lithium battery gives a stable and reversible electrochemical reaction. 19 Fig 2.9 Cyclic voltammogram (CV) curve of TCB at a scan rate of 100 mV/s Fig 2.10 Cycling performance of TCB (from 1 to 100 cycle) 20 The cycling performance of TCB as anode in the lithium battery is shown in Fig. 2.10. And the charge-discharge performance of TCB is shown in Fig. 2.11. The initial specific charge and discharge capacity are 765.9 mAh/g and 895.0 mAh/g, respectively. After 100 cycles, the specific charge and discharge capacity gradually drop to 397.0 mAh/g and 404.1 mAh/g, resulting in a decline of 48.2 % and 54.8 %. The reason why specific capacity gradually decreases in this experiment is that the active material, i.e. TCB, slowly dissolved in the electrolyte. Besides, Li-ions could be trapped inside the TCB material, leading to an irreversible electrochemical reaction. However, the coulombic efficiency is c.a. 100 % at all times. Judging from the results, the TCB material clearly possesses relatively stable performance in the cycling aspect. Fig 2.11 Charge-discharge curve of TCB 21 Rate capability experiments are usually regarded as the essential part in testing a material’s electrochemical performances. In this experiment, the TCB battery was set at different current discharge rates: 1 C, 2 C, 4 C, 8 C, 10 C, 20 C, 30 C, 20 C, 10 C and 1 C, which are shown in the Fig. 2.12 below. The number for each running cycles of different rate is 10. According to the results, the specific charge and discharge capacity are stable at different rates. Once recovers from a high discharge rate (30 C), the performance of TCB material remains stable at relatively low discharge rate (10 C and 20 C). However, when decrease to a rate of 1 C, the specific capacity gradually drops from over 650 mAh/g to 600 mAh/g in 20 cycles. In terms of the coulombic efficiency, the lithium battery using TCB material presents excellent performance. The efficiency remains at 100 % in either inter-rate cycles or intra-rate cycles. However, it should be noted that the coulombic efficiency for transition points of different rates is not 100 %. Fig 2.12 Rate performance of TCB at different rates 22 2.3.2.2 PTCB’s electrochemical performance as anode material in Li-ion battery Aiming at comparing the electrochemical performance of PTCB and TCB and exploring the reversibility of PTCB in the lithium battery system, button batteries containing PTCB are first tested for the CV performance. As can be seen in Fig. 2.13, PTCB presents similar curves when compared with TCB. The range of scanning voltage is still from 0.1 V to 3.0 V with a scan rate of 100 mV/s. Besides their similar chemical structure, the amine moieties inside the PTCB are the ones that determine the oxidation-reduction potential, which is from 0.8 V to 1.0 V as well. However, the reduction peak shifts a little bit from the second to the sixth cycle, indicating that the stability and reversibility are worse than that of TCB. Fig 2.13 Cyclic voltammogram (CV) curve of PTCB at a scan rate of 100 mV/s 23 The cycling performance of PTCB as cathode in the lithium battery is shown in Fig. 2.14. The charge-discharge performance of TCB is shown in Fig. 2.15. The initial specific charge and discharge capacity are 473.7 mAh/g and 619.2 mAh/g, respectively. These two values are definitely less than that of TCB, indicating that TCB should be more suitable as the lithiumion anode. After 100 cycles, the specific charge and discharge capacity drop to 167.9 mAh/g and 169.2 mAh/g, respectively, resulting in a decrease of the capacity to 64.6 % and 72.3 %. Normally, the solubility and stability of a material should be enhanced after polymerization. However, results between TCB and PTCB regarding the specific capacity certainly do not follow this rule. Judging from the results, the PTCB material seems to be less applicable for potential energy-related systems. Further researches should be conducted to explore the factors which lead to the deterioration of PTCB’s electrochemical performances. Fig 2.14 Cycling performance of PTCB (from 1 to 100 cycle) 24 Fig 2.15 Charge-discharge curve of PTCB 2.4 Extended application of PTCB in photocatalysis area 2.4.1 Fundamentals of photocatalysis Over the past few years, increasing attention is paid on photochemical synthesis to solve energy shortage issues because sunlight is the ultimate energy source [67]. Generally, there are two modes of photochemical activation. The first one is done by electrontransfer process, which is called photoinduced electron-transfer sensitization or photoredox catalysis. The second one is through indirect generation of electronically excited organic substrates, which is named photosensitization or energy-transfer photocatalysis [67]. Thus, “photocatalysis” is used to describe both types of photochemical activations, since some similarities do exist in these two types [68]. 25 Much of the recent studies regarding the visible light photocatalysis are focused on photogenerated organic radicals. Since photocatalysts do have the ability in generating organic radicals, substantial attention has been placed on the radical chemistry. Aside from photogeneration effect, photocatalytic activation of amines is a popular research field. For example, amines, as the common additives in the visible light photocatalysis, are widely investigated as the reductants in recent studies [68, 69]. Thus, if properly used, some polymers containing amines moieties can be synthesized and tested for their photocatalysis properties, except their original functions. Amine-containing organics may work as multifunctional materials. 2.4.2 Principles of PTCB as a photocatalyst Besides serving as the anode material in the Li-ion battery system, the PTCB can also be applied as a photocatalyst. The schematic diagram of PTCB-based photocatalysis experiment is shown in Fig. 2.16. As can be seen, O2 can be reduced to O2- in the presence of PTCB and light. The electron donor is oxidized after donating the electron to PTCB. In the end, O2- and electron donor will react with each other to form the product. 26 Fig 2.16 The schematic diagram of PTCB-based photocatalysis In this experiment, benzylamine was first chosen as the electron donor to investigate the whole mechanism. Then, optimizations on parameters and experiment conditions were conducted, including different catalyst used, different solvents effect, the importance of light, the presence of oxygen, etc. At each different circumstance, the products conversion rate and catalyst’s selectivity were chosen as the evaluation standard. 2.4.3 Experiment procedure of photocatalysis Into a quartz reaction flask, 20mg of PTCB, 1 mmol of organic substrates and 2 mL of acetonitrile were added. The reactor was connected to a water chiller to maintain the temperature throughout the reaction. The reactor was covered with a septum, which was connected with an oxygen balloon through a needle. While stirring, the reaction mixture was exposed to a UV-VIS lamp, equipped with UV filter, for 2 hours or until the reaction was completed. GC-MS was used to check the progress of the reaction and to identify the product. 27 Once the reaction was finished, the catalyst was filtered and washed with ethyl acetate. Then, the filtrate was concentrated by rotatory evaporator and subjected to further characterizations. 2.4.4 Photocatalysis performance of PTCB Although PTCB presents lower specific capacity in lithium battery system, its performance as the photocatalyst is absolutely outstanding. In this experiment, benzylamine was chosen as the electron donor. And the whole process is shown in Fig. 2.17 and Fig. 2.18. Fig. 2.17 The schematic diagram of photocatalysis when PTCB worked as the catalyst and benzylamine worked as electron donor Fig. 2.18 The further reaction of photocatalysis when benzylamine worked as electron donor 28 From the schematic diagram, it is clear that PTCB can act as a photocatalyst, which means its quality and quantity will not be changed. O2 is consumed and changed to H2O in the end. As for the benzylamine, it will be transformed to benzyl-benzylidene-amine. Further experiments were targeted at optimizing the conditions to obtain a higher conversion rate with less reaction or light-exposed time. In these experiments, different experiment conditions were investigated when PTCB was applied as the photocatalyst, which is shown in Fig. 2.19. As can be seen in Fig. 2.19, when acetonitrile is used as the solvent and PTCB as the photocatalyst, the conversion rate and selectivity can reach up to 100 % and 98 % in the condition that oxygen is continuously bubbled in and the system was exposed to light for 2 hours. Lacking either oxygen or light will result in tiny conversion rate, which suggests that oxygen and visible light played vital roles in photocatalysis. If the solution is changed to methanol, the performance is poor (33 %). Besides, TCB presents extremely low conversion rate when operates at the optimal experiment condition (2 h light-exposed time, oxygen provided). Different photocatalysts were also tested for their photocatalytic performance, which is shown in Fig. 2.19. Comparing to a commercialized photocatalyst, TiO2, PTCB outcompetes its performance regarding the conversion rate, indicating huge potential in practical application. Moreover, PTCB’s performance as photocatalyst also exceeds the graphene-C3N4 catalyst system, which is the best metal free photocatalyst up to now. 29 Fig. 2.19 The conversion rate and selectivity of PTCB, graphene-C3N4 and TiO2 for photocatalysis experiment. For PTCB, different experiment conditions were investigated, including no oxygen, changing of solution and no light conditions. 2.5 Conclusion and future work 2.5.1 Main conclusion PTCB were successfully synthesized at lab-scale from TCB. A series of characterization were applied, including SEM, FTIR, TGA and UV-VIS spectrum. Through polymerization, the PTCB’s chemical structure is certainly changed with the conservation of amine moieties. Its micro-wire microstructure is observed and determined through SEM as well. Through the electrochemical experiments, it can be concluded that TCB shows a relative stable and better performance than PTCB in the lithium-ion battery system. According to the CV curves, TCB’s oxidation-reduction potential is 0.8-1.0 V. The initial specific charge and discharge capacity is 765.9 mAh/g and 895.0 mAh/g, respectively. After 100 cycles, the 30 specific charge and discharge capacity drop to 397.0 mAh/g and 404.1 mAh/g. Besides, the rate capability performances at different rates are rather stable when TCB is applied in the lithium-ion battery system. For PTCB, its oxidation-reduction potential is similar to that of TCB, suggesting that same reversible electrochemical reactions take place inside the cell. However, the cycling and charge-discharge performance are worse than those of TCB. The initial specific charge and discharge capacity are 473.7 mAh/g and 619.2 mAh/g. After 100 cycles, the specific charge and discharge capacity drop to 167.9 mAh/g and 169.2 mAh/g, respectively. Nevertheless, the PTCB’s performance as a photocatalyst is outstanding when compared to commercial viable catalyst TiO2 and graphene-C3N4 system. By applying PTCB in the system, the O2 and the electron donor can form useful products with the presence of visible light. It is found that by using acetonitrile as the solvent and in the presence of oxygen, the conversion rate and selectivity can achieve 100 % and 98 %, respectively, after 2 hours’ exposure under visible light. In conclusion, TCB seems to have larger potential as the anode material in the lithium-ion battery system considering its stability and relatively high specific capacity. The organic polymer PTCB, which is derived from the small organic molecule, possesses a bright future as an effective and highly selective photocatalyst. Thus, both the monomer and the polymer, as the novel organic materials, would contribute much to future energy-related applications. 31 2.5.2 Future work Lots of investigations have been done to test the performance of PTCB as the anode material of Li-ion battery. However, the PTCB’s electrochemical performance was not satisfying. Since it possesses same function group (amine moieties) with TCB, possible optimization can be conducted in the future to enhance its cycling stability and maximum specific capacity. Since polymer is usually more insoluble than organic monomer, in-situ XRD and other advanced techniques can be applied to investigate the reason which leads to poor stability. Besides, since PTCB is an effective photocatalyst, other electron donors aside from benzylamine can be tested to synthesize a series of organic chemicals. PTCB may also be applied in other energy-related systems, such as a water-splitting catalyst. If this target can be achieved, PTCB can eventually be regarded as a multifunctional material. 32 Chapter 3: Inorganic anode material derived from small organic molecules for Na-ion battery This chapter was at first targeted at preparing a novel inorganic material, Sb-carbon composite, which was derived from small organic molecules. The material was further thoroughly characterized to get a clear picture of its surface structures and main elemental compositions. Its electrochemical performance was further investigated to explore their potentials and possible applications in practical sodium battery systems. 3.1 Background Recent studies on comparison between similar materials applied in Li-ion and Na-ion systems indicate that Na has larger ionic radius and larger mass, which requires larger channels and interstitial sites on the hosts to accept Na+ [70]. Besides, since sodium-ion battery is a relatively new area, novel materials for electrode, electrolyte and spacer are required to enhance battery system and improve the performance. Among all the factors, it is believed that the biggest obstacle is to obtain high-performance electrode with simple synthetic method, non-toxic, environmental friendly, cost-effective and long-lasting features [71]. As for anode materials, recent studies have explored several potential types. The first one is the carbon-based anode material, such as petroleum cokes [72-74], carbon black [75] and carbon fibers [76]. Since carbon materials are rich in nanocavities and nanopores, it will be 33 much easier for Na+ insertion. The second type is the metal oxide anode material, such as Na2Ti3O7 (intercalation) [77], NiCo2O4 (conversion) [78] and Sb2O4 (alloying) [79]. The last type is the intermetallic anode material. Recently, Sn/Sb/C nanocomposites are applied in the sodium-ion battery system with a specific capacity of 544 mAh/g and coulombic efficiency of over 98 % [80]. Obviously, sodium-ion battery is a complementary energy storage system to current, widely used Li-ion system. If proper electrode materials could be found, we could harvest its potential in the future. 3.2 Experiment scheme and approaches All the reagents and solutions used in this chapter were purchased from Sigma Aldrich (Singapore). Tube sealing-tube experiment also applied in this section due to the product’s sensitivity to oxygen. In order to carbonize the small organic antimonial salt into Sb-carbon composite, the tube furnace was chosen as the ideal equipment for this reaction. The heating temperature and time were 600-800 ℃ and 2 hours, respectively. In order to investigate the elemental composition and the degree of carbonization, the black product was first sent for elemental analysis (EA) and inductively coupled plasma optical emission spectrometry (ICP-OES) to determine the mass fraction of carbon and antimony. 34 X-ray diffraction (XRD) together with Raman spectroscopy were applied to qualitative determine the presence and ratio of carbon and antimony inside the product. Transmission electron microscopy (TEM) was further applied to study the surface and micro-structure of the product both in the film status and fine particle status. TEM Characterization XRD of inorganic material Synthesis of Sb- Raman spectroscopy Elemental analysis carbon composite Electrochemical performance as CV Cycling feature anode materials Rate feature Fig. 3.1 The experiment scheme of chapter 3 3.3 Results and Discussion 3.3.1 Preparation of nano Sb-carbon composite Organic antimonial salt (100 mg) was carefully placed at the bottom of a quartz tube. The tube was then sealed under the vacuum condition. After the tube was sealed, it was placed inside the tube furnace for carbonization. It was heated at 600-800 ℃ for 2 hours. The white powder was gradually turned to black liquid after gasification. The gas was well distributed inside the sealing tube that when the temperature started to fall it coated on the surface of the 35 tube uniformly in the end. The sealing tube containing black film products was carefully drawn out from the furnace after proper cooling. Afterwards, the sealing tube was opened to obtain the product inside. Ethanol was injected into the tube through the opening. The tube was then placed in the ultrasonic machine for separation. The temperature was maintained below 50 ℃ and the product was sonicated for 30 mins. After 3 days, ethanol was completely removed from the beaker. The black film inside the beaker was carefully collected and further grounded with the mortar. The final product appears as black fine particles and is stored inside a dry box. 3.3.2 Characterization of nano Sb-carbon composite After opening the sealing tube, parts of the film inside the tube was taken out to observe the macro-structure (Fig. 3.2). From Fig. 3.2, the internal surface of the black film seems to be rather smooth and glossy. However, it is also very brittle and can be easily turned into small pieces. Fig 3.2 The macro-surface structure of the Sb-carbon composite The micro-structure of the film’s surface is further explored with the TEM. The side view and top view of the film are shown in Fig. 3.3 and 3.4, respectively. 36 As can be seen from both pictures, besides the regular cut, the film seems to be rather smooth and uniform, which is in accordance with the macro-structure. Fig. 3.3 Transmission electron microscopy (TEM) picture of the Sb-carbon composite (side view) Fig. 3.4 TEM picture of the Sb-carbon composite (top view) 37 After grinding the film into fine particles, the micro-structure is shown in Fig. 3.5 and 3.6. 5 nm Fig. 3.5 The spherical structure of Sb-carbon composite (low magnification) 1 nm Fig. 3.6 The spherical structure of Sb-carbon composite (high magnification) It is obvious that the Sb-carbon composite has the spherical structure according to above figures. Further XRD and Raman spectrum is applied to determine the composition inside the 38 material. As can be seen in Fig. 3.7, the peaks regarding the relatively intensity is in coincidence with the antimony standard spectrum (PDF #85-1322). Besides, according to Fig. 3.8, the D and G peaks, which are all characteristic peaks of carbon, are well observed in the (214) (300) (018) (122) (116) (107) (024) (202) (015) (006) (104) (110) (003) (012) Relatively intensity (a.u.) Raman spectroscopy. PDF#85-1322 20 40 60 2 Theta (degree) Fig. 3.7 X-ray diffraction (XRD) of Sb-carbon composite (Sb) Fig. 3.8 The Raman spectrum of Sb-carbon composite (carbon) 39 80 The effect of temperature during the reaction process is extensively studied, as shown in Table 3.1. As can be seen, the higher temperature is provided during the reaction, less antimony will remain in the final product. Because the melting point of antimony is around 630 ℃, the temperature is set at 700 ℃ to guarantee thorough mixing in this section. Higher temperature resulted in greater loss of antimony. Table 3.1 Elemental analysis of Sb-carbon composite at different temperatures Temperature (℃) Sb C 600 40.87% 41.10% 700 35.10% 52.47% 800 31.27% 54.14% 3.3.3 Electrochemical performance of Sb-carbon composite 3.3.3.1 Assembly of Na-ion battery A series of sodium battery experiments were conducted by using the inorganic Sb-carbon composite as the anode material. The carbon material was first completely dried in the oven and then ground into fine particles together with graphene and carbon nanotubes (CNT). After proper binding, the mixture was placed and coated on the copper sheet by using a spreader (50 micrometer width). The coated copper sheet was dried under the room temperature overnight to remove the remaining water. Afterwards, the coated copper sheet was compressed with the roller and cut into small disks. These disks together with shells of button battery and spacers were once again placed inside the vacuum oven overnight. 40 All the assembly procedures were conducted inside the glove box. After the assembly process, the sodium batteries were taken out from the glove box and stabilized for at least 18 hours. All the well-functioning sodium batteries were tested for the cyclic voltammogram, chargedischarge performance and rating capabilities at different rates. In this experiment, LAND battery test system (Wuhan, China) was used to document the electrochemical performance of both TCB and PTCB as the anode material in the sodium battery. All the data were collected and further processed by using the Origin 8.0 software. 3.3.3.2 Electrochemical performance as anode material in Na-ion battery The CV curve of Sb-carbon composite at a scan rate of 100 mV/s is shown in Fig. 3.9. Following reactions will happen on Sb-carbon composite anode: Charge   Na 3Sb Sb+3Na + +3e-  (3-1) Discharge As can be seen, the oxidation peaks of all six cycles, which occurs at 0.87 V, are exactly the same with each other, indicates that one-step deinsertion of Na is happened [81]. As for the reduction part, the peaks shifted from the first (single peak) to the third cycle (multiple peaks). The most plausible explanation is that only one step of insertion of Na is happened at the first cycle. However, for the third cycle, multiple steps of insertion of Na happened as follows: amorphous Sb → amorphous Na3Sb → Na3Sb (hexagonal/cubic phase) → Na3Sb(hexagonal phase) [48, 81]. After the third cycle, the reduction peaks in the last three 41 cycles are the same (0.37 V to 0.66V), indicating that the insertion pattern and mechanism of Na have stabilized. Current / A 1st cycle 2nd cycle 3rd cycle 4th cycle 5th cycle 0.0 0.5 1.0 1.5 2.0 + Voltage / V v.s. Na /Na Fig. 3.9 The CV curve of Sb-carbon composite at a scan rate of 100 mV/s 1400 100 1200 80 1000 60 800 600 40 4C 2C 1C 400 200 0 0 10 20 30 20 40 Coulombic efficiency (%) Specific capacity (mAh g-1) In order to further confirm its stability, performances at different rates are shown in Fig. 3.10. 0 50 Cycle number / N Fig. 3.10 The specific capacity and coulombic efficiency of Sb-carbon composite in Na-ion battery 42 For each rate, 50 cycles are applied to investigate the material’s stability and specific capacity. As can be seen in Fig. 3.10, the specific capacity is c.a. 800 mAh/g when the battery is tested in the 1 C condition. Under 2 C rate, the specific capacity drops to 630 mAh/g. The performance is so stable that the curve is actually a straight line throughout the 50 cycles. If the rate is further increased to 4 C, the specific capacity drops to c.a. 580 mAh/g. However, the coulombic efficiencies under 1, 2 and 4 C rate are always above 99 %. Due to this material’s stable performance and rather huge specific capacity, the Sb-carbon composite definitely has a great potential for energy-related applications. 3.4 Conclusion and future work 3.4.1 Main conclusion Sb-carbon composite was successfully synthesized in this study. Afterwards, the powder was determined largely consisted of carbon (52 %) and antimony (35 %) through a series of characterization methods. Electrochemical tests prove that this inorganic anode material possessed large specific capacities (800 mAh/g @ 1C, 630 mAh/g @ 2C and 580 mAh/g @ 4C). Its oxidation potential is 0.87 V and reduction potentials are 0.37 V to 0.66 V. Besides, it displays rather stable performance and high coulombic efficiency (>99%) under different rate conditions. Thus, Sb-carbon composite shows promising application as anode material in sodium-ion battery. 43 3.4.2 Future work For the inorganic Sb-carbon composite, a series of optimization on preparation process can be further investigated in future study, such as temperature of tube furnace, argon/hydrogen ratio and grinding method. According to the CV, the insertion mechanism of Na to the Sb-carbon composite is not fully investigated. Thus, in-situ XRD together with other characterization approaches can be applied to determine the specific changes and insertion mechanism. Finally, by using it as the anode material in the sodium-ion system, whole-cell experiments can be conducted considering its excellent cycling stability and specific capacity. 44 Chapter 4: Supporting Information 4.1 Reagents information All the reagents used in this study are shown in Table 4.1. Table 4.1 All the reagents used in this study No. Regents Company Comments Sigma Aldrich Purity ≥ 97 % 2 1,3,5-tri(9H-carbazol-9yl)benzene CDCl3 3 Chloroform Sigma Aldrich HPLC grade, ≥ 99.5 % 4 HCl (37 %) Sigma Aldrich AR grade, 35~37 % 5 Methanol Sigma Aldrich Anhydrous, ≥ 99.8 % 6 Tetrahydrofuran (THF) Sigma Aldrich HPLC grade, ≥ 99.9 % 7 Polyvinylidene fluoride Sigma Aldrich Mw~534000, powder 8 N-methyl-2-pyrrolodone Sigma Aldrich 1M LiPF6 in EC/DMC MTI company electrolyte 1M LiTFSI in DOL/DME Solvionic electrolyte 1 9 10 For NMR Purity ≥ 99 % Used as electrolyte Used as electrolyte Although TCB is commercially available from Sigma Aldrich (Singapore), it can also be synthesized, which will greatly minimize the cost with the same product purity. The NMR spectrum of synthesized TCB is shown in Fig. 4.1 and 4.2. The 1H NMR of TCB is shown in Fig. 4.1: 1H NMR (CDCl3, 300 MHz) δ 8.19-8.17 (d, J=6.0 Hz, 6H), 7.97 (s, J=2.94Hz, 3H), 7.69-7.67 (d, J=6.10 Hz, 6H), 7.51-7.46 (t, J=6.13 Hz, 6H), 7.37-7.32 (t, J=6.15 Hz, 6H). The 13 C NMR of TCB is shown in Fig. 4.2: C NMR (CDCl3, 300 Hz) δ 140.37, 140.27, 13 126.36, 123.81, 123.47, 120.72, 120.59, 109.65. 45 Fig. 4.1 The 1H NMR spectrum of TCB (CDCl3, 300 Hz) Fig. 4.2 The 13C NMR spectrum of TCB (CDCl3, 300 Hz) According to the results of 1H NMR and 13C NMR, the product is determined as TCB with high purity. No interfering materials are found inside the product. 46 4.2 Equipment information All major equipment used in this study is shown in Table 4.2. Table 4.2 All the equipments used in this study No. 1 2 3 4 5 Equipments Nuclear magnetic resonance (NMR) Elemental analysis (EA) Inductively coupled plasma optical emission spectrum (ICPOES) Thermogravimetric analysis (TGA) Scanning Electron Microscopy (SEM) Company Type Bruker, Germany Ultra-shield 300 Hz Elementar, Germany Vario micro cube PekinElmer, USA Dual-view optima 5300 DV ICP-OES TA Instruments, USA DTA-TGA 2960 JOEL, USA JSM-6701F 6 X-ray Diffaction (XRD) Bruker, Germany 7 UV-VIS spectrum Transmission electron microscopy (TEM) Shimadzu, Japan D8 advance powder XRD UV-3600 JOEL, USA JEM-1400 Plus 8 9 Glove box 10 Battery tester Vacuum atmospheres, Omni-lab USA Land, China CT2001A 11 Electronic balance Mettler-Toledo, USA 12 Tube furnace 13 Compact hydraulic crimping machine XS105 Single-zone tube MTI corporation, USA furnace MTI corporation, USA MSK-110 47 Chapter 5: References 1. Tarascon, J.M. and M. Armand, Issues and challenges facing rechargeable lithium batteries. Nature, 2001. 414(6861): p. 359-367. 2. Armand, M. and J.M. Tarascon, Building better batteries. Nature, 2008. 451(7179): p. 652-657. 3. Poizot, P. and F. Dolhem, Clean energy new deal for a sustainable world: from nonCO2 generating energy sources to greener electrochemical storage devices. Energy & Environmental Science, 2011. 4(6): p. 2003-2019. 4. Nagaura, T. and K. Tozawa, Prog. Batteries Solar Cells, 1990. 9: p. 209. 5. Chen, H., et al., From biomass to a renewable LixC6O6 organic electrode for sustainable Li-ion batteries. Chemsuschem, 2008. 1(4): p. 348-355. 6. Williams, D.L., J.J. Byrne, and J.S. Driscoll, A High Energy Density Lithium/Dichloroisocyanuric Acid Battery System. Journal of the Electrochemical Society, 1969. 116(1): p. 2-&. 7. Yoshino, A., The Birth of the Lithium-Ion Battery. Angewandte Chemie-International Edition, 2012. 51(24): p. 5798-5800. 8. Novak, P., et al., Electrochemically active polymers for rechargeable batteries. Chemical Reviews, 1997. 97(1): p. 207-281. 9. Liang, Y., Z. Tao, and J. Chen, Organic Electrode Materials for Rechargeable Lithium Batteries. Advanced Energy Materials, 2012. 2(7): p. 742-769. 10. Han, X., et al., Aromatic carbonyl derivative polymers as high-performance Li-ion storage materials. Advanced Materials, 2007. 19(12): p. 1616-+. 11. Le Gall, T., et al., Poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene): a new organic polymer as positive electrode material for rechargeable lithium batteries. Journal of Power Sources, 2003. 119: p. 316-320. 12. Armand, M., et al., Conjugated dicarboxylate anodes for Li-ion batteries. Nature Materials, 2009. 8(2): p. 120-125. 13. Malini, R., et al., Conversion reactions: a new pathway to realise energy in lithiumion battery-review. Ionics, 2009. 15(3): p. 301-307. 14. Cabana, J., et al., Beyond Intercalation-Based Li-Ion Batteries: The State of the Art and Challenges of Electrode Materials Reacting Through Conversion Reactions. Advanced Materials, 2010. 22(35): p. E170-E192. 15. Jiang, J., et al., Recent Advances in Metal Oxide-based Electrode Architecture Design for Electrochemical Energy Storage. Advanced Materials, 2012. 24(38): p. 5166-5180. 48 16. Nitta, N. and G. Yushin, High-Capacity Anode Materials for Lithium- Ion Batteries: Choice of Elements and Structures for Active Particles. Particle & Particle Systems Characterization, 2014. 31(3): p. 317-336. 17. Cho, J., Porous Si anode materials for lithium rechargeable batteries. Journal of Materials Chemistry, 2010. 20(20): p. 4009-4014. 18. Jeannine, R.S. and J. Song, Energy & Environmental Science, 2011. 4. 19. Wu, H. and Y. Cui, Designing nanostructured Si anodes for high energy lithium ion batteries. Nano Today, 2012. 7(5): p. 414-429. 20. Obrovac, M.N. and L. Christensen, Structural changes in silicon anodes during lithium insertion/extraction. Electrochemical and Solid State Letters, 2004. 7(5): p. A93-A96. 21. Obrovac, M.N. and L.J. Krause, Reversible cycling of crystalline silicon powder. Journal of the Electrochemical Society, 2007. 154(2): p. A103-A108. 22. Li, H., et al., A high capacity nano-Si composite anode material for lithium rechargeable batteries. Electrochemical and Solid State Letters, 1999. 2(11): p. 547549. 23. Guo, J. and C. Wang, A polymer scaffold binder structure for high capacity silicon anode of lithium-ion battery. Chemical Communications, 2010. 46(9): p. 1428-1430. 24. Mazouzi, D., et al., Silicon Composite Electrode with High Capacity and Long Cycle Life. Electrochemical and Solid State Letters, 2009. 12(11): p. A215-A218. 25. Bridel, J.S., et al., Key Parameters Governing the Reversibility of Si/Carbon/CMC Electrodes for Li-Ion Batteries. Chemistry of Materials, 2010. 22(3): p. 1229-1241. 26. Magasinski, A., et al., Toward Efficient Binders for Li-Ion Battery Si-Based Anodes: Polyacrylic Acid. Acs Applied Materials & Interfaces, 2010. 2(11): p. 3004-3010. 27. Ge, M., et al., Porous Doped Silicon Nanowires for Lithium Ion Battery Anode with Long Cycle Life. Nano Letters, 2012. 12(5): p. 2318-2323. 28. Kovalenko, I., et al., A Major Constituent of Brown Algae for Use in High-Capacity Li-Ion Batteries. Science, 2011. 334(6052): p. 75-79. 29. Etacheri, V., et al., Exceptional Electrochemical Performance of Si-Nanowires in 1,3Dioxolane Solutions: A Surface Chemical Investigation. Langmuir, 2012. 28(14): p. 6175-6184. 30. Ohara, S., et al., A thin film silicon anode for Li-ion batteries having a very large specific capacity and long cycle life. Journal of Power Sources, 2004. 136(2): p. 303306. 31. Fuchsbichler, B., et al., High capacity graphite-silicon composite anode material for lithium-ion batteries. Journal of Power Sources, 2011. 196(5): p. 2889-2892. 49 32. Jung, D.S., et al., Spray Drying Method for Large-Scale and High-Performance Silicon Negative Electrodes in Li-Ion Batteries. Nano Letters, 2013. 13(5): p. 20922097. 33. Magasinski, A., et al., High-performance lithium-ion anodes using a hierarchical bottom-up approach. Nature Materials, 2010. 9(4): p. 353-358. 34. Zhang, C., et al., An elastic germanium-carbon nanotubes-copper foam monolith as an anode for rechargeable lithium batteries. Rsc Advances, 2013. 3(5): p. 1336-1340. 35. Ren, J.-G., et al., Germanium-graphene composite anode for high-energy lithium batteries with long cycle life. Journal of Materials Chemistry A, 2013. 1(5): p. 18211826. 36. Lee, H., et al., Surface-stabilized amorphous germanium nanoparticles for lithiumstorage material. Journal of Physical Chemistry B, 2005. 109(44): p. 20719-20723. 37. Chockla, A.M., et al., Solution-Grown Germanium Nanowire Anodes for Lithium-Ion Batteries. Acs Applied Materials & Interfaces, 2012. 4(9): p. 4658-4664. 38. Hwang, I.-S., et al., A binder-free Ge-nanoparticle anode assembled on multiwalled carbon nanotube networks for Li-ion batteries. Chemical Communications, 2012. 48(56): p. 7061-7063. 39. Xue, D.-J., et al., Improving the Electrode Performance of Ge through Ge@C CoreShell Nanoparticles and Graphene Networks. Journal of the American Chemical Society, 2012. 134(5): p. 2512-2515. 40. Yuan, F.-W., H.-J. Yang, and H.-Y. Tuan, Alkanethiol-Passivated Ge Nanowires as High-Performance Anode Materials for Lithium-Ion Batteries: The Role of Chemical Surface Functionalization. Acs Nano, 2012. 6(11): p. 9932-9942. 41. Yan, C., et al., Highly Conductive and Strain-Released Hybrid Multilayer Ge/Ti Nanomembranes with Enhanced Lithium-Ion-Storage Capability. Advanced Materials, 2013. 25(4): p. 539-544. 42. Wolfenstine, J., et al., Experimental confirmation of the model for microcracking during lithium charging in single-phase alloys. Journal of Power Sources, 2000. 87(12): p. 1-3. 43. Zhou, X., L.-J. Wan, and G.Y. -G., Advanced Materials, 2013. 44. Park, C.-M., et al., High-rate capability and enhanced cyclability of antimony-based composites for lithium rechargeable batteries. Journal of the Electrochemical Society, 2007. 154(10): p. A917-A920. 45. Caballero, A., J. Morales, and L. Sanchez, A simple route to high performance nanometric metallic materials for Li-ion batteries involving the use of cellulose: The case of Sb. Journal of Power Sources, 2008. 175(1): p. 553-557. 50 46. Park, C.-M. and H.-J. Sohn, Novel antimony/aluminum/carbon nanocomposite for high-performance rechargeable lithium batteries. Chemistry of Materials, 2008. 20(9): p. 3169-3173. 47. Sung, J.H. and C.-M. Park, Amorphized Sb-based composite for high-performance Liion battery anodes. Journal of Electroanalytical Chemistry, 2013. 700: p. 12-16. 48. Darwiche, A., et al., Better Cycling Performances of Bulk Sb in Na-Ion Batteries Compared to Li-Ion Systems: An Unexpected Electrochemical Mechanism. Journal of the American Chemical Society, 2012. 134(51): p. 20805-20811. 49. Baggetto, L., et al., Intrinsic thermodynamic and kinetic properties of Sb electrodes for Li-ion and Na-ion batteries: experiment and theory. Journal of Materials Chemistry A, 2013. 1(27): p. 7985-7994. 50. Zhu, Y., et al., Electrospun Sb/C Fibers for a Stable and Fast Sodium-Ion Battery Anode. Acs Nano, 2013. 7(7): p. 6378-6386. 51. Qian, J., et al., High capacity Na-storage and superior cyclability of nanocomposite Sb/C anode for Na-ion batteries. Chemical Communications, 2012. 48(56): p. 70707072. 52. Galland, C., et al., Lifetime blinking in nonblinking nanocrystal quantum dots. Nature Communications, 2012. 3. 53. Song, Z. and H. Zhou, Towards sustainable and versatile energy storage devices: an overview of organic electrode materials. Energy & Environmental Science, 2013. 6(8): p. 2280-2301. 54. Shacklette, L.W., et al., POLYACETYLENE AND POLYPHENYLENE AS ANODE MATERIALS FOR NONAQUEOUS SECONDARY BATTERIES. Journal of the Electrochemical Society, 1985. 132(7): p. 1529-1535. 55. Zhu, L.M., et al., An all-organic rechargeable battery using bipolar polyparaphenylene as a redox-active cathode and anode. Chemical Communications, 2013. 49(6): p. 567-569. 56. Walker, W., et al., Electrochemical characterization of lithium 4,4 '-tolanedicarboxylate for use as a negative electrode in Li-ion batteries. Journal of Materials Chemistry, 2011. 21(5): p. 1615-1620. 57. Abouimrane, A., et al., Sodium insertion in carboxylate based materials and their application in 3.6 V full sodium cells. Energy & Environmental Science, 2012. 5(11): p. 9632-9638. 58. Park, Y., et al., Sodium Terephthalate as an Organic Anode Material for Sodium Ion Batteries. Advanced Materials, 2012. 24(26): p. 3562-3567. 59. Zhao, L., et al., Disodium Terephthalate (Na2C8H4O4) as High Performance Anode Material for Low-Cost Room-Temperature Sodium-Ion Battery. Advanced Energy Materials, 2012. 2(8): p. 962-965. 51 60. Mermilliod, N., J. Tanguy, and F. Petiot, A STUDY OF CHEMICALLY SYNTHESIZED POLYPYRROLE AS ELECTRODE MATERIAL FOR BATTERY APPLICATIONS. Journal of the Electrochemical Society, 1986. 133(6): p. 1073-1079. 61. Macdiarmid, A.G., et al., POLYANILINE - ELECTROCHEMISTRY AND APPLICATION TO RECHARGEABLE BATTERIES. Synthetic Metals, 1987. 18(1-3): p. 393-398. 62. Gospodinova, N. and L. Terlemezyan, Conducting polymers prepared by oxidative polymerization: Polyaniline. Progress in Polymer Science, 1998. 23(8): p. 1443-1484. 63. Zhou, M., et al., Redox-Active Fe(CN)(6)(4-)-Doped Conducting Polymers with Greatly Enhanced Capacity as Cathode Materials for Li-Ion Batteries. Advanced Materials, 2011. 23(42): p. 4913-4917. 64. Feng, J.K., et al., Polytriphenylamine: A high power and high capacity cathode material for rechargeable lithium batteries. Journal of Power Sources, 2008. 177(1): p. 199-204. 65. Yao, M., et al., Redox active poly(N-vinylcarbazole) for use in rechargeable lithium batteries. Journal of Power Sources, 2012. 202: p. 364-368. 66. Chen, Q., et al., Microporous Polycarbazole with High Specific Surface Area for Gas Storage and Separation. Journal of the American Chemical Society, 2012. 134(14): p. 6084-6087. 67. Schultz, D.M. and T.P. Yoon, Solar Synthesis: Prospects in Visible Light Photocatalysis. Science, 2014. 343(6174): p. 985-+. 68. Fagnoni, M., et al., Photocatalysis for the formation of the C-C bond. Chemical Reviews, 2007. 107(6): p. 2725-2756. 69. Tucker, J.W. and C.R.J. Stephenson, Shining Light on Photoredox Catalysis: Theory and Synthetic Applications. Journal of Organic Chemistry, 2012. 77(4): p. 1617-1622. 70. Ong, S.P., et al., Voltage, stability and diffusion barrier differences between sodiumion and lithium-ion intercalation materials. Energy & Environmental Science, 2011. 4(9): p. 3680-3688. 71. Slater, M.D., et al., Sodium-Ion Batteries. Advanced Functional Materials, 2013. 23(8): p. 947-958. 72. Doeff, M.M., et al., ELECTROCHEMICAL INSERTION OF SODIUM INTO CARBON. Journal of the Electrochemical Society, 1993. 140(12): p. L169-L170. 73. Alcantara, R., J.M.J. Mateos, and J.L. Tirado, Negative electrodes for lithium- and sodium-ion batteries obtained by heat-treatment of petroleum cokes below 1000 degrees C. Journal of the Electrochemical Society, 2002. 149(2): p. A201-A205. 74. Zhecheva, E., et al., EPR study on petroleum cokes annealed at different temperatures and used in lithium and sodium batteries. Carbon, 2002. 40(13): p. 2301-2306. 52 75. Alcantara, R., et al., Carbon black: a promising electrode material for sodium-ion batteries. Electrochemistry Communications, 2001. 3(11): p. 639-642. 76. Thomas, P., J. Ghanbaja, and D. Billaud, Electrochemical insertion of sodium in pitch-based carbon fibres in comparison with graphite in NaClO4-ethylene carbonate electrolyte. Electrochimica Acta, 1999. 45(3): p. 423-430. 77. Senguttuvan, P., et al., Na2Ti3O7: Lowest Voltage Ever Reported Oxide Insertion Electrode for Sodium Ion Batteries. Chemistry of Materials, 2011. 23(18): p. 41094111. 78. Alcantara, R., et al., NiCo2O4 spinel: First report on a transition metal oxide for the negative electrode of sodium-ion batteries. Chemistry of Materials, 2002. 14(7): p. 2847-+. 79. Sun, Q., et al., High capacity Sb2O4 thin film electrodes for rechargeable sodium battery. Electrochemistry Communications, 2011. 13(12): p. 1462-1464. 80. Xiao, L., Y. Cao, and J. Xiao, High capacity, reversible alloying reactions in SnSb/C nanocomposites for Na-ion battery applications. Chemical Communications, 2012. 48(27): p. 3321-3323. 81. He, M., et al., Monodisperse Antimony Nanocrystals for High-Rate Li-ion and Na-ion Battery Anodes: Nano versus Bulk. Nano Letters, 2014. 14(3): p. 1255-1262. 53 [...]... energy storage equipment and devices hold the key to the future development of human society The electrode is an essential part of the battery system and is absolutely vital in the improving current energy conversion efficiency of batteries Due to the deterioration of current environment and increasing awareness of protecting earth, attentions are now focused on not only the electrochemical performance of. .. spectrum of TCB (CDCl3, 300 Hz) 46 XI Chapter 1: Literature Review Nowadays, people are paying increasing attention to energy and environmental issues Scientists from all over the world try their best to enhance the electrochemical performance of current energy storage techniques and explore new energy sources as well as energy- related materials with outstanding performance [1, 2] Efficient and portable energy. .. energy- related applications are critically needed to fulfill the increasing energy demand in our modern society However, few studies are targeted on organic Li-ion anode material and inorganic Na-ion anode material derived from small molecules In this thesis, lab-scale synthesis and preparations are conducted to obtain organic and inorganic materials, which are polycarbazole and Sb-carbon 9 composite, both derived. .. 1H NMR and 13 C NMR were conducted by using the CDCl3 as the solvent All the data was processed by the software to get a clear identification of the compound Thermal gravity analysis (TGA) was then conducted to compare the difference of thermostability of both TCB and PTCB under N2 protection The initial temperature was the room temperature (about 28 ℃) The heating speed was 10 ℃ per minute until it... 2.6 FTIR spectrum of TCB and PTCB Further FTIR experiment was conducted to investigate the infrared transmittance of the product As can be seen in Fig 2.6, the main absorptions of infrared light for TCB and PTCB occur between the wavenumber of 1000-1700 cm-1 According to the spectra, the characteristic peaks of PTCB matches to that of TCB’s, although the peak intensities between 1200 and 1300 cm-1 have... roller and cut into small disks These disks together with shells of button battery and spacers were once again placed inside the vacuum oven overnight After heating for at least 8 hours inside the vacuum oven, the disks, shells of button battery and spacers were taken out and transferred into the glove box All the assembly procedures 18 were conducted inside the glove box, where the concentrations of both... at 0.8-1.0 V From the second to the sixth cycle, the oxidation peak and reduction peak coincide with each other The positions of oxidation and reduction peaks stay the same Thus, the TCB material inside the lithium battery gives a stable and reversible electrochemical reaction 19 Fig 2.9 Cyclic voltammogram (CV) curve of TCB at a scan rate of 100 mV/s Fig 2.10 Cycling performance of TCB (from 1 to 100... series of lithium battery experiments are conducted by using TCB and PTCB as the anode materials The TCB and PTCB were first completely dried in the oven and then ground into fine particles together with super-P Afterwards, all the materials were placed inside a small glass bottle After adding a few drops of polyvinylidene fluoride (PVDF) solution (11%), the bottle was placed on magnetic stirrer During the. .. Fig 1.2 The redox mechanisms of three types of organic materials 8 Fig 1.3 Typical inorganic/organic electrode materials and their 8 corresponding redox voltage and specific capacity for rechargeable lithium batteries Fig 2.1 Novel organic polymers containing conjugated amine 11 structure and their theoretical specific capacity Fig 2.2 The schematic of the main chemical reaction in PTCB 12 synthesis. .. 2.2 The schematic of the main chemical reaction in PTCB synthesis Upon the acquirement of both TCB and PTCB, a series of characterizations were applied to determine the substance, investigate the microstructure and other features The scheme is shown in Fig 2.3 The Ultra-shield 300 Hz nuclear magnetic resonance (NMR) spectrometer 12 (Brucker, Germany) was first used to determine TCB Both 1H NMR and