Dissertations / Theses on the topic 'High-performance lithium-ion battery (LIB)'

The performance and lifetime of lithium-ion batteries are strongly influenced by their composition. One category of critical components are electrolyte additives, which are included primarily to stabilize electrode/electrolyte interfaces in the battery cells by forming passivation layers. The presented study aimed to identify and study such an additive that could form a hydrogen-evolution-suppressing solid electrolyte interphase (SEI) in lithium-ion batteries based on aqueous electrolytes. A promising molecular additive, ethyl 2,2-difluoroacetate (EDFA), was found to hold the qualities required for an SEI former and was herein further analyzed electrochemically. Analysis of the battery cells were performed with linear sweep voltammetry and cyclic voltammetry with varying scan rate and EDFA concentrations. Results show that both 1 and 10 w-% EDFA in the electrolyte produced hydrogen-evolution-suppressing SEI:s, although the higher concentration provided no apparent benefit. Lithium-ion full-cells based on LiMn2O4 vs. Li4Ti5O12 active materials displayed poor, though partly reversible, dis-/charge cycling despite the operation of the electrode far outside the electrochemical stability window of the electrolyte. Inclusion of reference electrodes in the lithium-ion cells proved to be immensely challenging with unpredictable drifts in their electrode potentials during operation. To summarize, HER-suppressing electrolyte additives are demonstrated to be a promising approach to stabilize high-voltage operation of aqueous lithium-ion cells although further studies are necessary before any practical application thereof can be realized. Electrochemical evaluation of the reaction mechanism and efficiency of the electrolyte additives relies however heavily on the use of reference electrodes and further development thereof is necessary.

Doctor of Philosophy
Department of Chemical Engineering
Placidus B. Amama
Advances in synthesis and processing of nanocarbon materials, particularly graphene, have presented the opportunity to design novel Li-ion battery (LIB) anode materials that can meet the power requirements of next-generation power devices. This thesis presents three studies on electrochemical behavior of three-dimensional (3D) nanostructured anode materials formed by pure graphene sheets and graphene sheets coupled with conversion active materials (metal oxides). In the first project, a microgel-templated approach for fabrication of 3D macro/mesoporous reduced graphene oxide (RGO) anode is discussed. The mesoporous 3D structure provides a large specific surface area, while the macropores also shorten the transport length of Li ions. The second project involves the use of a novel magnetic field-induced method for fabrication of wrinkled Fe3O4@RGO anode materials. The applied magnetic field improves the interfacial contact between the anode and current collector and increases the stacking density of the active material. The magnetic field treatment facilitates the kinetics of Li ions and electrons and improves electrode durability and the surface area of the active material. In the third project, poly (methacrylic acid) (PMAA)-induced self-assembly process was used to design super-mesoporous Fe3O4@RGO anode materials and their electrochemical performance as anode materials is also investigated. To establish correlations between electrode properties (morphological and chemical) and LIB performance, a variety of techniques were used to characterize the samples. The significant improvement in LIB performance of the 3D anodes mentioned above is largely attributed to the unique properties of graphene and the resulting 3D architecture.

Kyoto University (京都大学)
0048
新制・課程博士
博士(人間・環境学)
甲第21877号
人博第906号
新制||人||216(附属図書館)
2018||人博||906(吉田南総合図書館)
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授 内本 喜晴, 教授 吉田 寿雄, 准教授 藤原 直樹
学位規則第4条第1項該当

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, May, 2020
Cataloged from the official PDF of thesis.
Includes bibliographical references (page 75).
This thesis explores the design of a water cooled lithium ion battery module for use in high power automotive applications such as an FSAE Electric racecar. The motivation for liquid cooling in this application is presented with an adiabatic battery heating simulation followed by a discussion of axial cooling based on the internal construction of an 18650 battery cell. A novel design is proposed, implementing soldering the negative terminal of electroplated 18650 battery cells directly to a metal core printed circuit board material as the critical cell-to-water interface that provides high thermal conductivity while maintaining electrical isolation. Cold plate design, sealing, and manufacturing is discussed and implemented concluding with pressure and leak testing of a scale test article. Cell soldering efficacy is explored through testing of various low temperature solder alloys, fluxes, and surface plating to make recommendations on full scale module builds. A single cell test article is constructed and tested to validate thermal performance expectations with preliminary results suggesting constant power discharge rates of up to 60 W per cell is possible without overheating, which greatly exceeds the power requirements of existing FSAE Electric vehicles built by MIT Motorsports. Further work is needed to quantify solder joint reliability and examine thermal gradients present at the full module and pack scales.
by Ethan Perrin.
S.B.
S.B. Massachusetts Institute of Technology, Department of Mechanical Engineering

A high performance battery management system (BMS) for large capacity cells was designed, built, and tested in a cycle of three revisions. The BMS was designed for use in applications where the battery pack configuration is unknown: parallel, series, or any combination. Each of the cells is equipped with its own battery management system to allow a peer-to-peer mesh network to monitor the safety of the cell. The BMS attached to each cell also is equipped with a 25A DC/DC converter to perform active balancing between cells in a string. This converter can transfer charge to (or from) a cell of higher potential and a cell of lower potential at the same time. The balancing circuit has a peak efficiency of 85.3%. The system draws only 53mA while balancing at 25A helping to increase low current performance. The system draws just under 5mA over all while active. Each BMS is equipped with one current sensor, which can measure ±800A with a second ±120A current range. Additionally, the board is equipped with coulomb counting to provide a better understanding of each cell. While this design has many great features, lack of full software support makes many of the subsystems dependent on user interaction to use. As a result, the design is not fully complete. Additionally, last minute design changes on the final revision resulted in detrimental effects to the accuracy of many of the analog circuits including the current sensing features.

"A ¡°mixed cathodes¡± LIB recycling process was first proposed and developed in the CR3 center at Worcester Polytechnic Institute. This process can efficiently and economically recover all the valuable metal elements in LIB waste. In the end of the recovery process, lithium, nickel, manganese, and cobalt ions will be recovered in the leaching solution. The objective of this work is to utilize the leaching solution to synthesis NixMnyCoz(OH)2 precursors and their corresponding LiNixMnyCozO2 cathode materials. The synthesized cathode materials can be used to build new LIBs, allowing the overall process to be a ¡°closed loop¡±. "

Thesis advisor: Udayan Mohanty
Rechargeable batteries, especially lithium ion batteries, have greatly transformed mobile electronic devices nowadays. Due to the ever-depletion of fossil fuel and the need to reduce CO2 emissions, the development of batteries needs to extend the success in small electronic devices to other fields such as electric vehicles and large-scale renewable energy storage. Li-ion batteries, however, even when fully developed, may not meet the requirements for future electric vehicles and grid-scale energy storage due to the inherent limitations related with intercalation chemistry. As such, alternative battery systems should be developed in order to meet these important future applications. This dissertation presents our successes in improving Li-O2 battery performance for electric vehicle application and integrating a redox flow battery into a photoelectrochemical cell for direct solar energy storage application. Li-O2 batteries have attracted much attention in recent years for electric vehicle application since it offers much higher gravimetric energy density than Li-ion ones. However, the development of this technology has been greatly hindered by the poor cycling performance. The key reason is the instability of carbon cathode under operation conditions. Our strategy is to protect the carbon cathode from reactive intermediates by a thin uniform layer grown by atomic layer depostion. The protected electrode significantly minimized parasitic reactions and enhanced cycling performance. Furthermore, the well-defined pore structures in our carbon electrode also enabled the fundamental studies of cathode reactions. Redox flow batteries (RFB), on the other hand, are well-suited for large-scale stationary energy storage in general, and for intermittent, renewable energy storage in particular. The efficient capture, storage and dispatch of renewable solar energy are major challenges to expand solar energy utilization. Solar rechargeable redox flow batteries (SRFBs) offer a highly promising solution by directly converting and storing solar energy in a RFB with the integration of a photoelectrochemical cell. One major challenge in this field is the low cell open-circuit potential, mainly due to the insufficient photovoltages of the photoelectrode systems. By combining two highly efficient photoelectrodes, Ta3N5 and Si (coated with GaN), we show that a high-voltage SRFB could be unassistedly photocharged and discharged with a high solar-to-chemical efficiency
Thesis (PhD) — Boston College, 2018
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry

Philosophiae Doctor - PhD
Lithium ion cathode systems based on composites of lithium iron phosphate (LiFePO₄), iron-cobalt-derivatised carbon nanotubes (FeCo-CNT) and polyaniline (PA) nanomaterials were developed. The FeCo-functionalised CNTs were obtained through in-situ reductive precipitation of iron (II) sulfate heptahydrate (FeSO₄.7H₂O) and cobalt (II) chloride hexahydrate (CoCl₂.6H₂O) within a CNT suspension via sodium borohydrate (NaBH₄) reduction protocol. Results from high Resolution Transmission Electron Microscopy (HRTEM) and Scanning Electron Microscopy (SEM) showed the successful attachment FeCo nanoclusters at the ends and walls of the CNTs. The nanoclusters provided viable routes for the facile transfer of electrons during lithium ion deinsertion/insertion in the 3-D nanonetwork formed between the CNTs and adjacent LiFePO₄ particles.

碩士
國立中央大學
化學研究所
98
The cathode of Li-ion battery after charge-discharged can produce a special structure named solid electrolyte interface (solid electrolyte interface, SEI), which helps lithium ion transmission during charge and discharge process, and improves the electrode stability. Charge capacity and safety can also be improved by improving SEI structure. The research presents two approaches to the improvement of SEI structure with the aim to produce high performance and safe lithium battery. This study is divided into two parts. The first part describes the modification of SEI through the addition of conducting polymer, which enhances both the C-rate capacity and cycle life. After screening several monomers, the thiophene monomer derivatives: 3,4-Ethylenedioxythiophene (EDOT) is found to be most effective for this purpose after electrochemical polymerization on the cathode surface. The conductive polymer is composed of electronic conducting main chain and ion conductive side-chain, enabling an efficient charge transfer on the interface of the LiFePO4 cathode particles. The addition, EDOT has effectively improved the C-Rate capability and life cycle. The improvement is found to increase with EDOT concentration but optimized at certain threshold. In presence of excess EDOT, longer activation cycle (during which polymerization is achieved) will be required to completely polymerize EDOT, and the interface may be too thick whcih blocks the litium insertion. In this system, 0.03M is the optimized concentration. The second part of the study is to improve lithium battery safety feature with the addition of functional molecules in the electrolytes. LiCoO2 is the most widely used cathode material in commercial lithium ion batteries, but the safety remains an issue which urgently needing improvement. In this research, barbituric acid (BTA) and its derivatives as well as conducting polymer were added to the electrolyte to improve lithium battery safety. The delay of exothermic temperature can be observed by differential scanning thermal calorimetry (DSC). Carefully balancing the component composition, it is found the battery performance and safety features can both be enhanced. Conventional safety technology uses flame retardants to reduce electrolyte flammability, temperature control is not satisfactory, and the charge capacity usually suffers greatly. In contrast, present approach achieved the thermal stability while still maintaining the charge capacity and long cycle life.

碩士
國立清華大學
化學工程學系
102
Germanium nanowires and copper nanowires were combined to manufacture germanium/copper nanowire fabrics with a layered inorganic nanowires structure. The fabrics are flexible and resilient. The lithium ion half cells made of the germanium/copper nanowire fabric with an electrolyte composed of FEC/DEC have excellent cycle performance and stability. After 500 cycles at a rate of 1C, the cell exhibited a reversible capacity of 830 mAh/g. The germanium/copper nanowire fabrics also exhibited high rate capacity, having a reversible capacity of 350 mAh/g at a rate of 20 C. In addition, it can allow ultrafast discharge at 50 C when charged at 1C. By calculating the total weight of the electrodes (active materials + conductive agents + binder + current collector) and comparing with the relevant literature, we found that the weight capacities of germanium/copper nanowire fabric electrode were 2~7 times higher than other types of germanium or silicon electrode. The germanium/copper nanowire fabric electrodes have potential for some applications which require rapid cycling rates and can significantly reduce battery weight. Furthermore, We prepared a large area Ge/Cu nanowire fabric anode (5 cm *8 cm) to assemble full cells with commercial Li(NiCoMn)O2 cathode. The full cells were able to power a lot of LEDs. This work demonstrated that our development of layered inorganic nanowires structure make progress toward practical Li-ion battery applications.

碩士
國立臺南大學
綠色能源科技學系碩士班
101
The issue of has been environmental protection earned lots of concern in recent years. Lithium-ion secondary battery is a green power components element for electric vehicle. Now, the demands for the battery performance are stringent, especially for the energy capacity and cycling stability. Comparing to other cathode materials, LiNi1/3Mn1/3Co1/3O2 composite has better cycling performance, higher working voltage. It has good potential for the application for on the cathode materials while the LiNi1/3Mn1/3Co1/3O2 deceases quickly after the reaction with the electrolyte at high voltage. The result showed that the electrolyte additive using in this working can help to form the solid electrolyte interphase (SEI) which can improve the cycling performance at high temperatures and working voltages. It also showed that the electrolyte additive 2wt% ADM can effectively improve the high temperature cycle performance after 100 cycles (keeps at 46.1%). The material analysis of LiNi1/3Mn1/3Co1/3O2 cathode after 100 cycles was investigated by scanning electron microscope and the inductively couple plasma optical emission spectrometry. These results confirmed that the SEI film can help to reduce the metal ion dissolution.

碩士
國立清華大學
材料科學工程學系
104
Owing to its high specific capacity (3579 mAh/g), silicon has become one of the most promising anode material candidates for use in lithium ion batteries. However, a 400% volume change during alloying is currently the biggest challenge toward their commercial application. The addition of graphene offers one potential method to overcome this problem. Due to its excellent mechanical properties, graphene is well suited to act as a buffer layer between silicon facilitating its large volume expansion. Hence, a facile route toward the optimization of graphene reduction is required. In this work, we demonstrate two different approaches leading to more efficient and low cost processes in order to exfoliate and reduce graphene oxide simultaneously within a few minutes. The difference between the two methods is the starting materials. First, the proposed method, so-called “dry exfoliation method” utilizes silicon carbide as an efficient microwave susceptor heat source. The second method, called “wet exfoliation method” uses graphene oxide solution with the addition of a reducing agent. In both cases, under microwave radiation, graphene oxide undergoes a rapid heating and reduction to graphene. To characterize our materials, we utilize Fourier transform infrared spectroscopy (FTIR) and X-Ray photoelectron spectroscopy (XPS), the loss of C=O peaks and OH peaks confirm the reduction of graphene oxide after treatment. Scanning Electron Spectroscopy (SEM) and Transmission Electron Microscopy (TEM) are used to morphologically characterize the material we synthesized. The cell performances of two different method of reducing graphene oxide are compared, showing capacity values of 1200mAh/g after 150 cycles for r-GO prepared from wet exfoliation method. Furthermore, by using the wet exfoliation method, additional precursors such as copper nanowires can be easily combined into the solution for further material enhancement. We believe this work presents a highly promising technique toward the low-cost production of reduced graphene oxide suitable for future Si based Li-ion battery applications.

Tin dioxide (SnO2) is considered one of the most promising anode materials for Lithium ion batteries (LIBs), due to its large theoretical capacity and natural abundance. However, its low electronic/ionic conductivities, large volume change during lithiation/delithiation and agglomeration prevent it from further commercial applications. In this thesis, we investigate modified SnO2 as a high energy density anode material for LIBs. Specifically two approaches are presented to improve battery performances. Firstly, SnO2 electrochemical performances were improved by surface modification using Atomic Layer Deposition (ALD). Ultrathin Al2O3 or HfO2 were coated on SnO2 electrodes. It was found that electrochemical performances had been enhanced after ALD deposition. In a second approach, we implemented a layer-by-layer (LBL) assembled graphene/carbon-coated hollow SnO2 spheres as anode material for LIBs. Our results indicated that the LBL assembled electrodes had high reversible lithium storage capacities even at high current densities. These superior electrochemical performances are attributed to the enhanced electronic conductivity and effective lithium diffusion, because of the interconnected graphene/carbon networks among nanoparticles of the hollow SnO2 spheres.

Research Doctorate - Doctor of Philosophy (PhD)
A high demand of energy in the field of potable electronics and electric vehicles has constantly stimulated the sustainable development of energy storage devices such as supercapacitors and electrochemical batteries toward higher energy density and power density. However, the performance of these clean energy devices depends mainly on the advanced materials that are used as electrodes for these devices. As these materials play a significant role in deciding the final efficiency and total cost of these devices, research focussed on the development of novel advanced electrode materials with unique electrochemical and textural properties including high conductivity and high specific surface area, tunable pore structures and chemical composition is needed. Among different electrode materials, nanostructured carbon based materials have been regarded as the most promising alternatives to replace the conventional graphite as the electrode material in electrochemical energy storage devices owing to their unique properties including controllable pore size on nanometer scales, high surface area and large pore volume. Especially, mesoporous carbon, carbon nanotube and graphene based materials have been extensively studied and reviewed. It is found out that the morphology or structure of these electrode materials highly influences on the enhanced electrochemical performances in energy storage devices. However, the achieved capacity is still remained low, and thus more intensive works are needed to make these devices commercially viable. In addition to the capacity, production cost of electrode materials should not be ignored for the large scale manufacturing in the industries. The cost of raw materials of electrodes must be low and synthesizing processes of the materials must be as simple and cheap as possible. Thus, research developments on the design of nanostructured carbon materials with controllable structures, simple fabrication processes, and high yield and enhanced electronic properties toward energy storage applications from cheap resources are needed. In this thesis, these challenges are being addressed by designing advanced nanoporous electrode materials with ordered porous structures, excellent textural parameters including tunable pore diameters and high specific surface areas and different chemical composition. This thesis begins with an overview of advancement and prospects for carbon nanomaterials for electrochemical energy storage technology including Li ion batteries, Na ion batteries and supercapacitors. The carbon nanomaterials include graphene, carbon nanotube, porous carbon, fullerene and their hybridized composites. The synthetic methods and properties of the nanomaterials are specifically explained and their electrochemical properties in the applications are investigated. Moreover, in order to advance the nano materials research, challenges and future perspectives are stressed at the end of the overview. Chapter 2 presents the design of highly ordered 3-dimensional mesoporous carbon for the supercapacitor application. The materials are synthesized via nanocasting approach using FDU-12 silica as a template. Pore size is varied with simply changing aging temperature of nanoporous silica templates. Highly sophisticated characterization techniques including powder X-ray diffraction, high resolution transmission electron microscopy (HR-TEM), high resolution scanning electron microscopy (HR-SEM), and N₂ adsorption‒ desorption techniques were employed to analyse the structure and textural properties of the synthesized mesoporous carbon materials. The characterization results prove that all the mesoporous carbons show 3-D mesostructure with highly ordered inter-connected mesopores. The prepared materials show excellent textural properties with tuneable pore diameters (5.7 to 9.4 nm) and a large specific surface area in the range from 451 to 1251 m² g^-1. The supercapacitive performance of the cubic structured mesoporous carbons is determined by cyclic voltammetry, electrochemical impedance and charge-discharge measurements. The materials show an excellent capacitive behaviour with a high specific capacitance of 315.3 F g^-1 at the current density of 1A g^-1, which is much higher than that of hexagonally ordered mesoporous carbon, activated carbon, and carbon nanotubes. The materials also show a superior cyclic stability and extremely low resistance. The high specific capacitance of these materials is attributed to the combination of excellent surface properties such as large specific surface area, large pore volume and uniform pore diameter, spherical morphology, and 3-D porous system with a cage type pores. Chapter 3 includes the design and development of highly ordered sulfur-doped mesoporous carbon nitrides (S-MCNs) for the sodium ion battery application. The materials are prepared through the hard template approach by employing a single precursor of dithiooxamide (DTO) as sources of carbon, nitrogen and sulfur. The interlayer space of the prepared materials is highly expanded upon S-doping on carbon nitride frameworks of S-MCNs. It is also confirmed that the chemical composition, crystallinity and textural properties of S-MCNs are simply tuned by varying the carbonization temperature from 500 to 700 °C. The crystallinity and textural properties of S-MCNs are optimized at carbonization temperature of 700 °C. In contrast to nonporous sulfur doped carbon nitrides (S-CNs) and nonporous graphitic carbon nitride (g-C₃N₄), the S-MCNs show much better Na⁺ intercalation property with a high discharge capacity of 304.2 mAh g^-1 in the 100^th cycle as well as an outstanding retention capability. Chapter 4 deals with the synthesis of highly ordered oxygen-doped mesoporous carbon nitrides (O-MCNs) with tailored pore size. These materials were successfully synthesized by using a single molecular precursor of carbohydrazide (CBZ) as a C, N, O containing precursor via a hard templating method using SBA-15 as a template. The sophisticated analysis such as near-edge X-ray absorption fine structure (NEXAFS), X-ray photoemission spectroscopy (XPS), UV-Vis spectroscopy and Fourier transform infrared spectroscopy (FT-IR) are used to find out the chemical bonding nature and existence of oxygen dopant in the materials. Highly ordered structure of O-MCNs is proved through Xray power diffraction (XRD) in low angle and transmission electron microscopy (TEM). The exceptional large surface area (~224.6 m² g^-1) and high pore volume (~0.58 cm³ g^-1) are proved by using N2 adsorption-desorption measurement. Moreover, the optimized O-MCN is used as an anode material for Li-ion battery and delivered 4 times higher reversible capacity than that of non-porous g-C₃N₄ with remarkable stability. Lastly, Chaper 5 addresses an overrole summary of each chapter and future perspectives of nano structured carbon based materials for the sustainable electrochemical applications such as Li ion batteries, Na ion batteries and supercapacitors.

碩士
大同大學
化學工程學系(所)
101
In this study, we used glucose–assisted hydrothermal synthesis to prepare SnO2/CNTs composites as anode material for lithium-ion batteries. The crystal structure and surface morphology were characterized by X-ray diffraction and scanning electrochemical microscopy, while the electrochemical performances including charge/discharge test, cyclic voltammetry, and electrode impedance spectroscopy were also investigated. The morphology of the composites after centrifugation showed that the SnO2 was well-coated on the carbon nanotubes. The discharge capacity of SnO2/CNTs composite with centrifugation at 0.1C, 1C, and 2C is maintained above 526 mAh/g, 470 mAh/g, and 412 mAh/g after 50 cycles, respectively. The results show that the discharge specific capacity of the sample with centrifugation is superior to that of the sample without centrifugation (450 mAh/g, 352 mAh/g, and 240 mAh/g) and pristine SnO2 (200 mAh/g, 150 mAh/g, 75 mAh/g). Hence, the composite of SnO2/CNTs after centrifugation revealed a higher electrochemical performance and much more stable cyclability than the composites without centrifugation. This indicates that CNTs indeed enhanced the characteristics of lithium ion diffusion and electronic conductivity in the electrode; as indicate by cyclic voltammetry and AC impedance spectra. As the result, SnO2 coated on CNTs does not change the electrochemical process, instead enhanced lithium diffusion, e;ectronic conductivity, and rate capability. On the other hand, the charge-transfer resistance and solution resistance also can be decreased.

碩士
國立臺灣科技大學
化學工程系
104
Lithium ion betteryhave been generally used in our live, i.e digital cameras, laptop and electric vehicles. Research and development has focused on improving the performance of existing battery systems, and safety. When lithium batteries charge/discharge , cathode is unstable .Recently, additives for cathode material in lithium ion battery.After an electrochemical process, these additives form the Solid Electolyte Interface (SEI) layer on the surface of cathode material, which can isolate cathode material to prevent contact of electroly and anode as well asenhance the safety in lithium ion batteries.In the study, bismaleimide (BMI), barbituric acid(BTA) and phenylsiloxane oligomer were used to synthesize BMI/BTA/APTES-PhSLX as an additive by Michael addition reaction and free radical reaction. The BMI/BTA/APTES-PhSLX as additive into Li1.2Ni0.2Mn0.6O2 material to investigate theeffect of performance and thermal stability on battery.According to charge/discharge and cycling tests,half-cell which added 130(phslx) increased the capacity and cycling performance. In the thermal exothermic,the 130(phslx) heat toapproximately 18.1% in room temperature.therefore, the cell would enhance the thermal stability when it operated after 40℃ all day.Finally, in cyclic voltammetry, the 130(phslx)’s cell has better diffusion of lithium ion.

The present thesis deals with the beneficial influence of nanostructuring on electrochemical performance of certain promising electrode and electrolyte materials for lithium-ion batteries (LIBs). Electrochemical performances of chosen electrodes and electrolytes have been presented in a systematic and detailed manner via studies related to both transport and lithium storage. Titanium dioxide (TiO2) or titania, a promising non-carbonaceous anode material for LIBs was chosen for the study. As part of the study, variety of nanostructured titania were synthesized. In general, all materials exhibited high lithium storage ( theoretical value for lithium storage in titania) and some of them showed exemplary rate capability, typically desired for modern lithium-ion batteries. Studies related to performance of these materials and mechanistics of lithium storage and kinetics are presented in Chapters 2-5. “Soggy sand” electrolyte, a promising soft matter electrolyte for LIBs was studied on the electrolyte side. Ion transport, mechanical strength and electrochemical properties of “soggy sand” electrolytes synthesized via dispersion of various surface chemically functionalized silica particles dispersed in model as well as LIB relevant electrolytes were studied in this thesis. Extensive physico-chemical and battery performance studies of “soggy sand” electrolytes are discussed in Chapters 6-8. A brief discussion of the contents and highlights of the individual chapters are described below: Chapter 1 briefly discusses the importance of electrochemical power sources as a viable green alternative to the combustion engine. Various facets of rechargeable LIBs, one of the most important electrochemical storage devices, are presented following the general discussion on electrochemical power devices. The importance of nanostructuring of electrodes with special emphasis on anodes for high lithium storage capacities and rate capabilities are also discussed in the opening chapter. The various advantages and disadvantages of the most commonly used electrolytes in LIB i.e. the liquid electrolytes are also discussed in Chapter 1. Suggestions for improvement of the physico-chemical properties of liquid electrolytes especially via nanostructuring (demonstrated via dispersions of fine oxide particles in liquid electrolytes in Chapters 6-8) using the concept of Heterogeneous doping are discussed in detail. A brief description on the importance of rheology for comprehension of soft matter microstructure is also provided in this chapter. Chapter 2 discusses composite of anatase titania (TiO2) nanospheres and carbon grown and self-assembled into micron-sized mesoporous spheres via a solvothermal synthesis route as prospective anode for rechargeable lithium-ion battery. The morphology and carbon content and hence the electrochemical performance are observed to be significantly influenced by the synthesis parameters. Synthesis conditions resulting in a mesoporous arrangement of an optimized amount of carbon and TiO2 exhibited the best lithium battery performance. The first discharge cycle capacity of carbon-titania mesoporous spheres (solvothermal reaction at 150 oC at 6 h, calcination at 500 oC under air, BET surface area 80 m2g-1) was 334 mAhg-1 (approximately 1 Li) at current rate of 66 mAg-1. High storage capacity and good cyclability is attributed to the nanostructuring (i.e. mesoporosity) of TiO2 as well as due to formation of a percolation network of carbon around the TiO2 nanoparticles. The micron-sized mesoporous spheres of carbon-titania composite nanoparticles also show good rate cyclability in the range (0.066-6.67) Ag-1. The electrochemical performance of the mesoporous carbon-TiO2 spheres has been compared with nonporous TiO2 spheres, normal mesoporous TiO2 and bulk TiO2. Implications of nanostructuring and conductive carbon interface on lithium insertion/removal capacity and insertion kinetics in nanoparticles of anatase polymorph of titania is discussed in Chapter 3. Sol-gel synthesized nanoparticles of titania (particle size ~ 6 nm) were hydrothermally coated ex situ with a thin layer of amorphous carbon (layer thickness: 2-5 nm) and calcined at a temperature much higher than the sol-gel synthesis temperature. The carbon-titania composite particles (resulting size  10 nm) displayed immensely superior cyclability and rate capability (higher current rates  4 Ag-1) compared to unmodified calcined anatase titania. The conductive carbon interface around titania nanocrystals enhances the electronic conductivity and inhibits crystallite growth during electrochemical insertion/removal thus preventing detrimental kinetic effects observed in case of un-modified anatase titania. The carbon coating of the nanoparticles also stabilized the titania crystallographic structure via reduction in the accessibility of lithium ions to the trapping sites. This resulted in decrease in the irreversible capacity observed in case of nanoparticles without any carbon coating. Chapter 4 discusses the morphology and electrochemical performance of mixed crystallographic phase titania nanotubes and nanosheets for prospective application as anode in rechargeable lithium-ion batteries. Hydrothermally grown nanotubes/nanosheets of titania (TiO2) and carbon/silver-titania (C/Ag-TiO2) comprise a mixture of both anatase and TiO2(B) crystallographic phases. The first cycle capacity (at current rate = 10 mAg-1) for bare TiO2 nanotubes was 355 mAhg-1 (approximately 1.06 Li), which is higher than both the theoretical capacity (335 mAhg-1) as well as reported values for pure anatase and TiO2(B) nanotubes. Higher capacity is attributed to a combination of presence of mixed crystallographic phases of titania as well as trivial size effects. The surface area of bare TiO2 nanotubes was very high being equal to 340 m2g-1. Surface modification of the TiO2 nanotubes via amorphous carbon and Ag nanoparticles resulted in significant improvement in battery performance. The first cycle irreversible capacity loss can be minimized via effective coating of the surface. Carbon coated TiO2 nanotubes showed superior performance than Ag nanoparticle coated TiO2 nanotubes in terms of long term cyclability. Unlike Ag nanoparticles which are randomly distributed over the TiO2 nanotubes, the effective homogeneous carbon coating forms an efficient percolation network for the conducting species thus exhibiting better battery performance. The C-TiO2 and Ag-TiO2 nanotubes showed a better rate capability i.e. higher capacities compared to bare TiO2 nanotubes in the current range 0.055-2 Ag-1. Although titania nanosheets retains mixed crystallographic phases, the lithium battery performance (first cycle capacity = 225 mAhg-1) is poor compared to TiO2 nanotubes. It is attributed to lower surface area (22 m2g-1) which resulted in lesser electrode/electrolyte contact area and inefficient transport pathways for Li+ and e-. Implications of iron on electrochemical lithium insertion/removal capacity of iron (Fe3+) doped anatase TiO2 is discussed in Chapter 5. Iron doped anatase TiO2 nanoparticles with different doping concentrations were synthesized by simple sol-gel method. The electrochemistry of anatase TiO2 is observed to be a strong function of concentration of iron (Fe3+). A high 1st cycle discharge capacity of 704 mAhg−1 (2.1 mol of Li) and 272 mAhg−1 (0.81 mol of Li) at the 30th discharge cycle with Coulombic efficiency greater than 96% has been observed for 5% iron (Fe3+) doped TiO2 at a current density of 75 mAg−1. Additional increase in the iron (Fe3+) concentrations deteriorates the lithium storage of TiO2. An improvement in lithium storage of more than 50% is noticed for 5% iron (Fe3+) doped TiO2 compared to pure anatase TiO2 which shows an initial discharge capacity of 279 mAhg−1. The anomalous lithium storage behavior in all the iron (Fe3+) doped TiO2 has been accounted, in addition to homogeneous Li insertion in the octahedral sites, on the basis of formation of metallic Fe and Li2O during initial lithiation process and subsequent heterogeneous interfacial storage between Fe and Li2O interface. Chapter 6 discusses in a systematic manner the crucial role of oxide surface chemical composition on ion transport in “soggy sand” electrolytes. A “soggy sand” electrolytic system comprising of aerosil silica functionalized with various hydrophilic and hydrophobic moeities dispersed in lithium perchlorate ethylene glycol solution ( = 37.7) was used for the study. Detailed rheology studies show that the attractive particle network in case of the composite with unmodified aerosil silica (with surface silanol groups) is most favorable for percolation in ionic conductivity as well as rendering the composite with beneficial elastic mechanical properties. Though weaker in strength compared to the composite with unmodified aerosil particles, attractive particle networks are also observed in composites of aerosil particles with surfaces partially substituted with hydrophobic groups. However, ionic conductivity is observed to be dependent on the size of the hydrophobic moiety. No spanning attractive particle network was formed for aerosil particles with surfaces modified with stronger hydrophilic groups (than silanol) and as a result no percolation in ionic conductivity was observed. The composite with hydrophilic particles was a sol contrary to gels obtained in case of unmodified aerosil and partially substituted with hydrophobic groups. Chapter 7 also discusses the influence of oxide surface chemical composition but additionally the role of solvent on ion solvation and ion transport of “soggy sand” electrolytes. Compared to the liquid electrolyte in Chapter 6, a lower dielectric constant liquid electrolyte was employed for the study in this chapter. A “soggy sand” electrolyte system comprising of dispersions of hydrophilic/hydrophobic functionalized aerosil silica in lithium perchlorate-methoxy polyethylene glycol solution ( = 10.9) was employed for the study. Static and dynamic rheology measurements again showed formation of an attractive particle network in case of the composite with unmodified aerosil silica (i.e. with surface silanol groups) as well as composites with hydrophobic alkane groups. While particle network in the composite with hydrophilic aerosil silica (unmodified) were due to hydrogen bonding, hydrophobic aerosil silica particles were held together via van der Waals forces. The network strength in the latter case (i.e. for hydrophobic composites) were weaker compared with the composite with unmodified aerosil silica. Both unmodified silica as well as hydrophobic silica composites displayed solid-like mechanical strength. However, this time around no enhancement in ionic conductivity compared to the liquid electrolyte was observed in case of the unmodified silica. This is attributed to the existence of a very strong particle network which leads to the “expulsion” of all conducting entities from the interfacial region between adjacent particles. The ionic conductivity for composites with hydrophobic aerosil particles displayed ionic conductivity as a function of the size of the hydrophobic chemical moiety. No spanning attractive particle network was observed for aerosil particles with surfaces modified with stronger hydrophilic groups (than silanol). The composite resembled a sol and no percolation in ionic conductivity was observed. Chapter 8 describes the influence of dispersion of uniformly sized mono-functional or bi-functional (“Janus”) particles on ionic conductivity in lithium battery solutions and it’s implications on battery performance. Mono-functionalized (hydrophilic or hydrophobic) and bi-functionalized Janus (hydrophilic and hydrophobic) particles form physical gels of varying strength over a wide range of concentration (0.1    0.4; , oxide volume fraction). While the composites with mono-functionalized particles display shear thinning typical of gels (due to gradual breaking up spanning particle network held together by hydrogen/van der Walls force), the bi-functionalized “Janus” particles exhibit both complementary properties of gel and sol. The latter observation is interpreted in terms of existence of both hydrogen and van der Waals force arising out of the particle arrangement which get perturbed under the influence of external shear. Composites with homogeneous hydrophilic surface group show the highest ionic conductivity whereas the homogeneous hydrophobic surfaces exhibit superior electrode/electrolyte interface stability and battery cyclability. The Janus particles did not show any enhancement in ionic conductivity however, battery performance is highly satisfactory taking intermediate values between the homogeneously functionalized hydrophilic and hydrophobic particle composites.

碩士
國立清華大學
材料科學工程學系
104
The increasing demand for advanced electronic devices and energy storage have stimulated significant interests in lithium ion battery development. Li based batteries are one of the most promising energy storage systems which as they are light-weight and energy-delivery efficient. Compared to the common graphite-anode system, Si is known to have highest theoretical specific capacitance making Si the most promising candidate for the next-generation anode materials for lithium batteries. However, large volume expansion and serious material pulverization after cycling lead to poor life times, and is the main stumbling block toward their commercialization. In this research, glancing angle deposition (GLAD) technique is utilized to deposit uniform and aligned helix Si nanostructures. By varying the rotation angle during GLAD, various helix Si nanostructures with differing porosities were deposited. With increasing numbers of rotation (3 to 48) the double layer capacitance, related to the surface area, increased to from 0.112 to 0.208 F/cm3. Additionally, the areal spacing also increases and results in occupation of Si nanostructure decreased from 77.5% to 73.77%. As a result, 48 cycle helix Si anode shows the best electrochemical performance with a volumetric specific capacity 846.55 mAh/cm3. Following a 100 cycle test, the anode is able to maintain 70% of its original volumetric specific capacity. However, the low conductivity of intrinsic silicon makes charge transfer of the electrons slow and also gives rise to incomplete alloying reactions with Li ions. To overcome this we annealed our anode with the aim of forming copper silicide, utilising the underlying copper substrate as a source. In doing so, the volumetric specific capacity was increased to 1706.68 mAh/cm3, using a 100 cycle test at charge/discharge rates as high as 0.25 C. Throughout this work detailed analysis was carried out, including X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), I-V characteristics (I-V) Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV), providing an understanding of our results and possibilities for future work. Furthermore, we believe that the adequate porosity and lower conductivity helps to minimize the enormous stress within the film structure by proving enough space for volume expansion, leading to a longer life time and better charge transfer and electrochemical performance.

Indiana University-Purdue University Indianapolis (IUPUI)
Since 1990s, rechargeable Li-ion batteries have been widely used in consumer electronics such as cell phones, global positioning systems (GPS), personnel digital assistants (PDA), digital cameras, and laptop computers. Recently Li-ion batteries received considerable attention as a major power source for electric vehicles. However, significant technical challenges still exist for widely deploying Li-ion batteries in electric vehicles. For instance, the energy density of Li-ion batteries is not high enough to support a long-distance commute. The Li-ion batteries used for the Nissan Leaf and Chevy Volt only can support 50 – 100 miles per charge. The cost of Li-ion battery packs in electric vehicles is still high. The battery pack for the Chevy Volt costs about $8,000, and the larger one in the Nissan Leaf costs about $12,000. To address these problems, new Li-ion battery electrode materials with high energy density and low cost should be developed. Among Li-ion battery cathode materials, vanadium pentoxide, V2O5, is one of the earliest oxides studied as a cathode for Li-ion batteries because of its low cost, abundance, easy synthesis, and high energy density. However, its practical reversible capacity has been limited due to its irreversible structural change when Li insertion is more than x = 1. Tremendous efforts have been made over the last twenty years to improve the phase reversibility of LixV2O5 (e.g., 0 ≤ x ≤ 2) because of vanadium pentoxides’ potential use as high capacity cathodes in Li-ion batteries. In this thesis, a new strategy was studied to develop vanadium pentoxide cathode materials with improved phase reversibility. The first study is to synthesize vanadium oxide cathodes via a new chemical route – creating a phase transformation from the vanadium sulfide to oxide. The β-Na0.33V2O5 was prepared via a new method of chemical synthesis, involving the chemical transformation of NaVS2 via heat-treatment at 600 °C in atmospheric air. The β-Na0.33V2O5 particles were well crystalized and rod-shaped, measuring 7–15 μm long and 1–3 μm wide with the formation of the crystal defects on the surface of the particles. In contrast to previous reports contained in the literature, Na ions were extracted, without any structural collapse, from the β -Na0.33V2O5 structure and replaced with Li ions during cycling of the cell in the voltage range, 1.5 V to 4.5 V. This eventually resulted in a fully reversible Li intercalation into the LixV2O5 structure when 0.0 ≤ x ≤ 2.0. The second study is to apply the synthesis method to LiVS2 for the synthesis of β׳-LixV2O5 for use as a high performance cathode. The synthesis method is based on the heat treatment of the pure LiVS2 in atmospheric air. By employing this method of synthesis, well-crystalized, rod-shaped β׳-LixV2O5 particles 20 – 30 μm in length and 3 – 6 μm in width were obtained. Moreover, the surface of β׳-LixV2O5 particles was found to be coated by an amorphous vanadium oxysulfide film (~20 nm in thickness). In contrast to a low temperature vanadium pentoxide phase (LixV2O5), the electrochemical intercalation of lithium into the β׳-LixV2O5 was fully reversible where 0.0 < x < 2.0, and it delivered a capacity of 310 mAh/g at a current rate of 0.07 C between 1.5 V and 4 V. Good capacity retention of more than 88% was also observed after 50 cycles even at a higher current rate of 2 C. The third study is the investigation of NaVS2 as a cathode intercalation material for sodium ion batteries. We have shown that reversible electrochemical deintercalation of x ~ 1.0 Na per formula unit of NaxVS2, corresponding to a capacity of ~200 mAh/g, is possible. And a stable capacity of ~120 mAh/g after 30 cycles was observed. These studies show that the new chemical synthesis route for creating a phase transformation from the vanadium sulfide to oxide by heat treatment in air is a promising method for preparing vanadium oxide cathode material with high reversibility. Although this sample shows a relatively low voltage range compared with other cathodes such as LiCoO2 (3.8 V) and LiFePO4 (3.4 V), the large capacity of this sample is quite attractive in terms of increasing energy density in Li-ion batteries. Also, NaVS2 could be a promising cathode material for sodium ion batteries.