There is a growing interest for relying on cleaner and more sustainable energy sources due to the negative side-effects of the dominant fossil-fuel based energy storage and conversion systems. Cleaner, electrochemical energy storage through lithium-ion batteries has gained considerable interest and market value for applications such as electric vehicles and renewable energy storage. However, capacity and rate (power) limitations of current lithium-ion battery technology hinder its ability to meet the high energy demands in a competitive and reliable fashion. Silicon is an element with very high capacity to Li-ion storage although commercially impractical due to its poor stability and rate capabilities. Nevertheless, it has been heavily researched with more novel electrode nanostructures to improve its stability and rate capability. It was found that silicon nanomaterials such as silicon nanowires have inherently higher stability due to mitigation of cracking and higher rate capability due to the short Li-ion diffusion distance. However, electrode compositions based only on silicon nanowires without additional structural features and a high conductive support do not have enough stability and rate capability for successful commercialization. One structural and conductive support of silicon materials studied in literature is graphene. Graphene-based electrodes have been reported as material capable of rapid electron transport enabling new strides in rate capabilities for Li ion batteries. This thesis presents a novel electrode nanostructure with a simple, inexpensive, scalable method of silicon nanwire synthesis on graphene nanosheets via nickel catalyst. The research herein shows the different electrode compositions and variables studied to yield the highest achievable capacity, stability and rate capability performance. The carbon coating methodology in addition to enhancing the 3D conductivity of the electrode by replacing typical binders with pyrolyzed polyacrylonitrile provided the highest performance results.

This thesis covers synthesis and characterisation of TiO2 nanotubes and TiO2 / Li4Ti5O12 composite nanotubes. The aim was to build batteries with high areal capacity and good rate capability. TiO2 nanotubes were synthesized by two step anodization of titanium metal foil and the composite electrodes were synthesized through electrochemical lithiation of TiO2 nanotubes. To improve the battery performance the TiO2 nanotubes were annealed at 350 °C in air atmosphere, while the composite electrodes were annealed in argon at 550 °C. The longest TiO2 nanotubes were measured to 42.5 μm. The 40 μm long nanotubes displayed an areal capacity of 1.0 mAh/cm2 and a gravimetric capacity of 89 mAh/g. Nanotubes having a length of 10 μm had an areal capacity of 0.33 mAh/cm2 and a gravimetriccapacity of 130 mAh/g. When cycled at high rates, 10C, the capacity of the 40 μm nanotubes was 0.25 mAh/cm2, using a current density of 9.3 mA. The capacity of the 40 μm long nanotubes were higher than for the 10 μm long, but the increase was not proportional to the increase in length. A composite electrode was successfully synthesized and was found to have a capacity of 0.25 mAh/cm2 at a rate of C/5.

This thesis details electrical and physical measurements of pulsed laser deposition-applied thin film coatings of Alumina, Ceria, and Yttria-stabilized Zirconia (YSZ) on a LiNi0.5Mn0.3Co0.2O2 (NMC) cathode in a Lithium ion battery. Typical NMC cathodes exhibit problems such as decreased rate performance and an opportunity for increased capacity exists by raising operation voltage beyond the electrolyte stability window. Very thin (~10 nm) coatings of stable oxides provide a pathway to solve both problems. As well, the electrochemical impedance spectra of the uncoated and coated cells were measured after different numbers of cycles to reveal the property variation in the cathode. Further understanding of the mechanism of rate performance enhancement and chemical protection by thin oxide coatings will continue to improve battery capability and open up new applications. Ceria-coated Li-NMC cells show the best capacity and rate performance in battery testing. Through electrochemical impedance spectroscopy (EIS), the surface film resistance was found to remain stable or even drop slightly after repeated cycling at high voltage. CeO2 is proposed as a coating for Lithium ion battery cathodes owing to its high chemical stability and the demonstrated but not yet well understood electrical conductivity. Alumina-coated cathode shows comparable performance as that of the uncoated cell in the early stage of the test, but through the course of testing the rate capability and recoverable capacity is improved. This is possibly due to Al2O3?s well-known abilities as HF scavenger and chemically inert nature. YSZ-coated cathode performs worse than the uncoated ones in terms of capacity, rate capability, and EIS-related figures of merit. The reason for the poor performance is not yet known, and repeatability tests are under way to verify performance. High voltage cycling reveals no obvious difference in irreversible loss between the coated or uncoated cells. The reason for the lack of distinction could be the relatively small percentage of surface coating compared to the thick doctor-blade processed cathode layer.

>Magister Scientiae - MSc / Spinel lithium manganese oxide (LiMn2O4), for its low cost, easy preparation and nontoxicity, is regarded as a promising cathode material for lithium-ion batteries. However, a key problem prohibiting it from large scale commercialization is its severe capacity fading during cycling. The improvement of electrochemical cycling stability is greatly attributed to the suppression of Jahn-Teller distortion (Robertson et al., 1997) at the surface of the spinel LiMn2O4 particles. These side reactions result in Mn2+ dissolution mainly at the surface of the cathode during cycling, therefore surface modification of the cathode is deemed an effective way to reduce side reactions. The utilization of a nanocomposite which comprises of metallic Cu and Au were of interest because their oxidation gives rise to a variety of catalytically active configurations which advances the electrochemical property of Li-ion battery. In this research study, an experimental strategy based on doping the LiMn2O4 with small amounts of Cu-Au nanocomposite cations for substituting the Mn3+ ions, responsible for disproportionation, was employed in order to increase conductivity, improve structural stability and cycle life during successive charge and discharge cycles. The spinel cathode material was synthesized by coprecipitation method from a reaction of lithium hydroxide and manganese acetate using 1:2 ratio. The Cu-Au nanocomposite was synthesized via a chemical reduction method using copper acetate and gold acetate in a 1:3 ratio. Powder samples of LiMxMn2O4 (M = Cu-Au nanocomposite) was prepared from a mixture of stoichiometric amounts of Cu-Au nanocomposite and LiMn2O4 precursor. The novel LiMxMn2O4 material has a larger surface area which increases the Li+ diffusion coefficient and reduces the volumetric changes and lattice stresses caused by repeated Li+ insertion and expulsion. Structural and morphological sample analysis revealed that the modified cathode material have good crystallinity and well dispersed particles. These results corroborated the electrochemical behaviour of LiMxMn2O4 examined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The diffusion coefficients for LiMn2O4 and LiMxMn2-xO4 obtained are 1.90 x10-3 cm2 / s and 6.09 x10-3 cm2 / s respectively which proved that the Cu-Au nanocomposite with energy band gap of 2.28 eV, effectively improved the electrochemical property. The charge / discharge value obtained from integrating the area under the curve of the oxidation peak and reduction peak for LiMxMn2-xO4 was 263.16 and 153.61 mAh / g compared to 239.16 mAh / g and 120 mAh / g for LiMn2O4. It is demonstrated that the presence of Cu-Au nanocomposite reduced side reactions and effectively improved the electrochemical performance of LiMn2O4.

Structured electrodes with tailored nanoscale morphology and chemistry are highly desirable for a range of applications. In particular, emerging energy storage applications such as thick Lithium-ion battery (LIB) electrodes and photoanodes for watersplitting require new electrode structures that simultaneously optimise electron, ion, and thermal transport. In this PhD thesis, advanced structured electrodes are fabricated by creating 3D carbon-inorganic hybrid architectures. In this process, patterned vertically aligned carbon nanotubes (CNT) were used as the structural scaffolds to shape the electrodes while inheriting the excellent thermal and electrical properties of CNTs. First, UV and colloidal lithographic patterning processes were developed to create micro- and nanopores respectively within the CNT structures. Those structures provide high surface area and conductive backbone for the synthesis of hybrid CNT-inorganic structures. Specifically, the parameter space to create honeycomb shaped CNT structures with pores ranging from 300~nm to 30~$\mu$m has been established. Next, the micro-pore CNT structures have been chemically modified with iron oxide using microwave-assisted, hydrothermal synthesis for fabricating high areal loading LIB anodes. The areal loading was increased by 120\% compared to a standard battery film while at the same time retaining a high capacity (900 mAhg$^{-1}$ at 0.2 C). Then thick electrodes with optimised diffusion pathways were created by coating the nanopatterned CNTs with silicon using physical vapour deposition. These electrode structures are up to 50\% thicker than previously reported structures and still retain a stable capacity (650 mAhg$^{-1}$) and a good high-rate performance. Finally, the honeycomb shaped CNT structures have been coated with bismuth vanadate using a hotcasting process and the electrode architecture has been optimized for good conductivity by the addition of a Pd/Au layer between the CNTs and the BiVO$_{4}$. The photoelectrode performance was measured and shows a clear increase in current density when exposed to light. Each of these novel electrodes illustrate how patterning vertically aligned carbon nanotube structures combined with inorganic surface modification enables the creation of advanced electrodes with new formfactors and improved performance in comparison to literature and to classic drop-casted battery films of the same materials.

This thesis includes five main studies/ first, in order to enhance the conductivity of LiTi204, a new doping strategy is used and LiTi204−xCx ramsdellite is successfully fabricated. It is found that unit cell parameters a and b decline while c increases with more carbon inserted. The conductivity of LiTi204−xCx increases with more carbon insertion. Material with more carbon shows better reversibility and lower electrochemical polarization observed from potentiostatic curve. The material has better retention rate and rate ability with more carbon substitute doped. LiTi203.925C0.0375 has 151 mAh∙g−1 capacity under current density of 100 mAh∙g−1 and capacity decreased by 5.57% after 100 cycles. Second, in order to improve the capacity of LiTi204−xCx, Ti204−xCx is successfully fabricated through topotactic oxidation. It is found that the lattice parameters b and c decline while a keeps stable. With more carbon inserted, the retention ability increases. Ti01.9625C0.0375 has the capacity 320 mAh∙g−1 under 200 mAh∙g−1 and capacity retention loss by 9.1% per 100 cycles due to the balance of high conductivity and disordered channel resistance. Third, in order to study the process of lithium insertion, the structures and the atom sites of LiTi204−xCx ( R ) are obtained through refinement of the neutron diffraction patterns. The unit cell parameters a and b increase while c keeps stable for more lithium, atoms insertion. The channels for lithium insertion become wider and more round with lithium arranged in a line when x rises in the range of 0 < x < 0.5. When the x increases to 1, the channels turn into ordered parallelogram. Fourth, the lithium-contained spinelloid (a potential cathode material) is explored, but it is not found in this work. But spinels LI1−0.5xFe2.5xM1−xP1−xO4 (M=Fe, Co, Ni, Mn) are found and phosphorous insertion makes the structure stable during cycling. At last, to enhance the energy density, the 3D electrode is fabricated in in-situ growth by infiltration method. By powder infiltration, the load of activity material reaches over 60% of electrode mass. The morphology is porous and the particle size of the activity material is 20nm. The energy density based on LiCoO2 (250 WH∙g−1) is much higher than that of the traditional (200 WH∙g−1) 2D electrode reported.

Made available in DSpace on 2018-08-01T21:58:48Z (GMT). No. of bitstreams: 1 tese_10827_Dissertação Jenifer Rigo Almeida - FINAL.pdf: 2105933 bytes, checksum: 17fccc5751be81765e75282388ce4b0c (MD5) Previous issue date: 2017-03-27 / Baterias de íon-Lítio (LIBs) exauridas são consideradas resíduos sólidos perigosos devido à presença de metais e compostos orgânicos em sua composição, representando desperdício de recursos naturais não renováveis e de metais valiosos quando descartadas. Este trabalho tem por objetivo fornecer dados quantitativos sobre a composição química do material ativo do cátodo (MAC) de diferentes LIBs exauridas visando monitorar variações com o passar dos anos e auxiliar nos processos de reciclagem do material. Os elementos Al, Co, Cr, Cu, Ga, Li, Mg, Mn, Ni, Ti e Zn foram determinados por espectrometria de emissão óptica com plasma indutivamente acoplado (ICP OES) após lixiviação ácida empregando 2,0 mol.L-1 de ácido cítrico (HCit) e H2O2 (0,25 mol.L-1) como alternativa ambientalmente favorável. As condições otimizadas para adequação do meio às curvas analíticas foram: para Al, Cu: Curva de HCit diluído 10 vezes sem padrão interno (PI); para Co, Li, Mn, Ni: Curva de HCit diluído 500 vezes sem PI; para Ga, Zn: Curva de HCit diluído 10 vezes com Y. O procedimento analítico empregado alcançou limites de detecção de 0,01 mg.L-1 para Al; 0,20 mg.L-1 para Co; 0,006 mg.L-1 para Cr; 0,02 mg.L-1 para Cu; 0,004 mg.L-1 para Ga; 0,02 mg.L-1 para Li; 0,0005 mg.L-1 para Mg; 0,07 mg.L-1 para Mn; 0,70 mg.L-1 para Ni; 0,0005 mg.L-1 para Ti e 0,007 mg.L-1 para Zn. A exatidão do procedimento foi confirmada por testes de adição e recuperação dos analitos obtendo-se valores entre 92-113 %. Os elementos majoritários Co (43-67 % m/m), Li (5,3-6,8 % m/m), Mn (0,8-8,2 % m/m), Ni (0,1-11,7 % m/m) e Al (0,06-3,2 % m/m) e os elementos minoritários Cr (0,0005-0,002 % m/m), Cu (0,01-0,05 % m/m), Mg (0,005-0,02 % m/m), Ti (0,001-0,07 % m/m), Ga (0,0009-0,03 % m/m) e Zn (0,009-0,05 % m/m) demonstraram que a composição do MAC pode variar de acordo com a capacidade e ano de fabricação. As baterias mais antigas foram as que apresentaram maiores teores de Co e Li. As baterias de menor capacidade foram as que continham os maiores teores de Mn e Ni, indicando que o Co foi substituído. O pó do MAC e o resíduo após lixiviação foram caracterizados por difratometria de raios X (DRX) obtendo-se LiCoO2 como composto principal, podendo ser reutilizado.

This thesis is dedicated to developing three different types of ferrocene-containing polymers for organic lithium-ion battery and resistive memory applications. Chapter 1 gives an overview of organic cathode-active materials, polymeric resistive memories and ferrocene-containing polymers. Furthermore, the previously reported applications of ferrocene-containing polymeric systems in electrochemical energy storage and electronical memory devices were also comprehensively summarized. In chapter 2, conjugated ferrocene-containing side-chain metallopolymers PFcFE1, PFcFE2, PFcFE3 and PFcFE4 were designed and synthesized via Sonogashira cross-coupling polycondensation. The charging-discharging processes of triphenyamine-based PFcFE1 and thiophene-modified PFcFE4 have been successfully studied as cathode materials. PFcFE1 composite electrode showed a capacity of 90 mAh g-1 and the cathode composed of PFcFE4 retained over 90% of the initial capacity after 100 charging-discharging cycles at 10 C. These results demonstrate the great potentials of these ferrocene-containing side-chain polymers as active cathode materials for organic lithium-ion battery applicaitons. Besides, all prepared ferrocene-containing metallopolymers PFcFE1, PFcFE2, PFcFE3 and PFcFE4 also exhibited nonvolatile resistive switching behaviors with the flash memory effect of PFcFE1, PFcFE2 and PFcFE3 as well as the WORM memory feature of PFcFE4, indicating the easily tuned memory properties by changing the chemical structures of the active polymeric backbones. It is also worth noting that the ITO/PFcFE1/Al memory device showed a high ON/OFF current ratio of 103 to 104, a low switch-on voltage of -1.0 V, a long retention time of 1000 s and a large read cycle number up to 105, which is superior to other reported ferrocene-containing memory examples. Chapter 3 focuses on the development of non-conjugated ferrocene-containing copolymers PVFVM1, PVFVM1-1, PVFVM2, PVFVM3, PVFVM4, PVFVM5 and PVFVM6 based on different heteroaromatic moieties which were prepared by AIBN initiated chain addition polymerization. The as-prepared copolymers PVFVM1 and PVFVM1-1 exhibited electrochemical characteristics of both ferrocene and triphenylamine pendants with reversible multiple redox waves at the half potentials of E1/2 = --0.06, 0.30, and 0.42 V (vs. Fc/Fc+). Notably, the composite electrode based on PVFVM1 afforded a discharge capacity of 102 mAh g--1 at 10 C, corresponding to 98% of its theoretical capacity. The cycle endurances of the active polymer electrodes composed of PVFVM1 or PVFVM1-1 were both evaluated for over 50 numbers and no significant capacity reduction over cycles were observed. On the other hand, initial I-V results of memory devices based on PVFVM1, PVFVM1-1, PVFVM2, PVFVM3, PVFVM4 and PVFVM6 also revealed their huge potentials in electronic information storage. The stability and reproducibility of the corresponding memory devices based on these materials will be futher evaluated in the near future. We used 1,1'-ferrocenediboronic acid bis(pinacol) ester to develop conjugated ferrocene-containing main-chain metallopolymers in chapter 4. All these rational designed metallopolymers FcMMP1, FcMMP2, FcMMP3 and FcMMP4 with one or two ferrocene moieties were produced via Suzuki cross-coupling polycondensation. Their structural information, molecular masses, photophysical features and thermal properties have been well studied. Electrochemical performances of the formed polymers were also examined to clarify their potential as cathode-active materials. Other charge-storage characteristics and switching behaviors of these prepared ferrocene-containing main-chain metallopolymers for organic battery and memory applications are under further investigation.

Power supply in any electronic system is a crucial necessity. Especially so in fully compliant personalized advanced healthcare electronic self-powered systems where we envision seamless integration of sensors and actuators with data management components in a single freeform platform to augment the quality of our healthcare, smart living and sustainable future. However, the status-quo energy storage (battery) options require packaging to protect the indwelling toxic materials against harsh physiological environment and vice versa, compromising its mechanical flexibility, conformability and wearability at the highest electrochemical performance. Therefore, clean and safe energy storage solutions for wearable and implantable electronics are needed to replace the commercially used unsafe lithium-ion batteries. This dissertation discusses a highly manufacturable integration strategy for a free-form lithium-ion battery towards a genuine mechanically compliant wearable system. We sequentially start with the optimization process for the preparation of all solid-state material comprising a ‘’Lithium-free’’ lithium-ion microbattery with a focus on thin film texture optimization of the cathode material. State of the art complementary metal oxide semiconductor technology was used for the thin film based battery. Additionally, this thesis reports successful development of a transfer-less scheme for a flexible battery with small footprint and free form factor in a high yield production process. The reliable process for the flexible lithium-ion battery achieves an enhanced energy density by three orders of magnitude compared to the available rigid ones. Interconnection and bonding procedures of the developed batteries are discussed for a reliable back end of line process flexible, stretchable and stackable modules. Special attention is paid to the advanced bonding, handling and packaging strategies of flexible batteries towards system-level applications. Finally, this work shows seamless integration of the developed battery module in an effective strategy to incorporate them into a complex architecture such as orthodontic domain in the human body. The developed optoelectronic system embedded in a 3D printed smart dental braces for enhanced enamel healthcare protection and overall healthcare cost reduction. These findings complement and provide power solution options in which flexibility of electronics is an added beneficial dimensionality to wearable biomedical and implantable devices.

Advancements in Li-ion batteries are needed especially for the development of electric vehicles and stationary energy storage. Prior research has shown mesoscale variations in electrode electronic conductive properties, which can cause capacity loss and uneven electrochemical behavior of Li-ion batteries. A micro-four-line probe (μ4LP) was used to measure electronic conductivity and contact resistance over mm-length scales in that prior work. This work describes improvements to overcome the challenge of unreliable surface contact between theμ4LP and the sample. Ultimately a second generation flexible probe called the micro-radial-surface probe (μ4LP) was designed and produced. The test fixture was also optimized to obtain consistent contact with the new measurement probe and to perform measurements at a lower force. The μ4LP was then used to study the effect of heterogeneity on calendering, which is the compression of electrode films to obtain a uniform thickness and desired porosity. The thickness, electronic conductivity and contact resistance of two cathodes and one anode were measured before and after calendering. The the spatial standard deviation divided by the mean was used as a measure of heterogeneity. The results show variability in conductive properties increased for two of the three samples after calendering, despite the increased uniformity in thickness of the electrodes. This suggests that additional quality control metrics are needed besides thickness to be able to identify uneven degradation and produce longer lasting batteries.