Carbonatos fosfatos isoestruturados do tipo sidorenkitas sÃo materiais com alto potencial de aplicaÃÃo em cÃtodos dos mais modernos tipos de baterias de sÃdio. Sua estrutura lamelar permite a inserÃÃo e extraÃÃo dos Ãons de sÃdio, que sÃo a principal fonte de forÃa eletromotriz da bateria. Utilizando um elemento muito mais abundante na crosta terrestre, esses dispositivos sÃo a grande promessa para substituiÃÃo da, jà bastante difundida, bateria de Ãons de lÃtio. PorÃm, o cÃtodo que contÃm as caracterÃsticas ideais para produzir o melhor desempenho, propiciando alta densidade de energia e estabilidade quÃmica, ainda està em desenvolvimento. A espectroscopia Raman continua sendo o melhor mÃtodo para caracterizar as propriedades destes compostos, pois contÃm a grande vantagem de ser altamente sensÃvel ao ambiente molecular das ligaÃÃes do oxigÃnio com os metais de transiÃÃo, o fÃsforo e o carbono. Nesta linha, realizamos um estudo de espectroscopia Raman em um conjunto de carbonatos fosfatos do tipo Na3MCO3PO4 (M = Mn, Fe, Co e Ni), obtidos por sÃntese hidrotÃrmica em microondas a 210 ÂC por 30 minutos. O sucesso na inserÃÃo de variados metais no interior de octaedros MO6, com raios iÃnicos distintos, produz uma alteraÃÃo no volume da cÃlula unitÃria do arranjo cristalino, modificando a distÃncia de equilÃbrio das ligaÃÃes atÃmicas, provocando uma alteraÃÃo substancial no nÃmero de onda dos seus modos normais de vibraÃÃo. Por isso, visto que informaÃÃes essenciais das propriedades quÃmicas e estruturais dos mais variados tipos de carbonatos fosfatos sÃo reveladas pela tÃcnica da espectroscopia Raman de forma confiÃvel, sua utilizaÃÃo se torna indispensÃvel para o desenvolvimento de mÃtodos e o planejamento de um material eficiente e comercialmente viÃvel para as inovadoras baterias de Ãons de sÃdio.

Polyanionic compounds have been heavily investigated as possible electrode materials in lithium- and sodium-ion batteries. Chief among these is lithium iron phosphate (LiFePO4) which adopts the olivine structure and has a potential of 3.5 V vs. Li/Li+. Many aspects of ion transport, solid-solution behaviour and their relation to particle size in olivine systems are not entirely understood. Morphology, unit cell parameters, purity and electrochemical performance of prepared LiFePO4 powders were greatly affected by the synthetic conditions. Partially delithiated olivines were heated and studied by Mössbauer spectroscopy and solid-solution behaviour by electron delocalization was observed. The onset of this phenomenon was around 470-500 K in bulk material but in nanocrystalline powders, the onset of a solid solution was observed around 420 K. The isostructural manganese member of this family (LiMnPO4) was also prepared hydrothermally. Owing to the thermal instability of MnPO4, partially delithiated LiMnPO4 did not display any solid-solution behaviour. Phosphates based on the tavorite (LiFePO4OH) structure include LiVPO4F and LiFePO4(OH)1-xFx which may be prepared hydrothermally or by solid state routes. LiVPO4F is a high capacity (2 electrons/transition metal) electrode material and the structures of the fully reduced Li2VPO4F and fully oxidized VPO4F were ascertained. Owing to structural nuances, the potential of the iron tavorites are much lower than that of the olivines. The structure of Li2FePO4F was determined by a combined X-ray and neutron diffraction analysis. The electrochemical properties of very few phosphates based on sodium are known. A novel fluorophosphate, Na2FePO4F, was prepared by both solid state and hydrothermal methods. This material exhibited two two-phase plateau regions on cycling in a half cell versus sodium but displayed solid-solution behaviour when cycled versus lithium, where the average potential was 3.3 V. On successive cycling versus Li a decrease in the sodium content of the active material was observed, which implied an ion-exchange reaction occurred between the material and the lithium electrolyte. Studies of polyanionic materials as positive electrode materials in alkali metal-ion batteries show that some of these materials, namely those which contain iron, hold the most promise in replacing battery technologies currently available.

Polyanionic compounds have been heavily investigated as possible electrode materials in lithium- and sodium-ion batteries. Chief among these is lithium iron phosphate (LiFePO4) which adopts the olivine structure and has a potential of 3.5 V vs. Li/Li+. Many aspects of ion transport, solid-solution behaviour and their relation to particle size in olivine systems are not entirely understood. Morphology, unit cell parameters, purity and electrochemical performance of prepared LiFePO4 powders were greatly affected by the synthetic conditions. Partially delithiated olivines were heated and studied by Mössbauer spectroscopy and solid-solution behaviour by electron delocalization was observed. The onset of this phenomenon was around 470-500 K in bulk material but in nanocrystalline powders, the onset of a solid solution was observed around 420 K. The isostructural manganese member of this family (LiMnPO4) was also prepared hydrothermally. Owing to the thermal instability of MnPO4, partially delithiated LiMnPO4 did not display any solid-solution behaviour. Phosphates based on the tavorite (LiFePO4OH) structure include LiVPO4F and LiFePO4(OH)1-xFx which may be prepared hydrothermally or by solid state routes. LiVPO4F is a high capacity (2 electrons/transition metal) electrode material and the structures of the fully reduced Li2VPO4F and fully oxidized VPO4F were ascertained. Owing to structural nuances, the potential of the iron tavorites are much lower than that of the olivines. The structure of Li2FePO4F was determined by a combined X-ray and neutron diffraction analysis. The electrochemical properties of very few phosphates based on sodium are known. A novel fluorophosphate, Na2FePO4F, was prepared by both solid state and hydrothermal methods. This material exhibited two two-phase plateau regions on cycling in a half cell versus sodium but displayed solid-solution behaviour when cycled versus lithium, where the average potential was 3.3 V. On successive cycling versus Li a decrease in the sodium content of the active material was observed, which implied an ion-exchange reaction occurred between the material and the lithium electrolyte. Studies of polyanionic materials as positive electrode materials in alkali metal-ion batteries show that some of these materials, namely those which contain iron, hold the most promise in replacing battery technologies currently available.

Philosophiae Doctor - PhD (Chemistry) / Nanomaterials have been found to undeniably possess superior properties than bulk structures across many fields of study including natural science, medicine, materials science, electronics etc. The study of nano-sized structures has the ability to address the current world crisis in energy demand and climate change. The development of materials that have various applications will allow for quick and cost effective solutions. Nanomaterials of Sn and Bi are the core of the electronic industry for their use in micro packaging components. These nanomaterials are also used as electrocatalysts in fuel cells and carbon dioxide conversion, and as electrodes for rechargeable sodium ion batteries. There are various methods used to make these nanostructures including solid state methods, hydrothermal methods, sputtering, and vacuum deposition techniques. These methods lack the ability to control the structure of material at an atomic level to fine tune the properties of the final product. This study aims to use E-ALD technique to synthesis thin films of Sn and Bi for various energy applications, and reports the use of E-ALD in battery applications for the first time. Thin films were synthesised by developing a deposition sequence and optimising this deposition sequence by varying deposition parameters. These parameters include deposition potential, and concentration of precursor solution. The thin films were characterised using cyclic voltammetry, linear sweep voltammetry, chronoamperometry for electrochemical activity. These were also characterised using scanning electron microscope for morphology, x-ray diffraction for crystal phases, energy dispersive spectroscopy for elemental mapping, and focused ion beam scanning electron microscope for thickness. The elemental content was analysed using electron probe micro analysis and inductively coupled plasma mass spectrometry. The electrochemical impedance charge and discharge profile were used for electrochemical battery tests.

abstract: This work describes the investigation of novel cathode and anode materials. Specifically, several mixed polyanion compounds were evaluated as cathodes for Li and Na-ion batteries. Clathrate compounds composed of silicon or germanium arranged in cage-like structures were studied as anodes for Li-ion batteries. Nanostructured Cu4(OH)6SO4 (brochantite) platelets were synthesized using polymer-assisted titration and microwave-assisted hydrothermal methods. These nanostructures exhibited a capacity of 474 mAh/g corresponding to the full utilization of the copper redox in an conversion reaction. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies were preformed to understand the mechanism and structural changes. A microwave hydrothermal synthesis was developed to prepare a series compounds based on jarosite, AM3(SO4)2(OH)6 (A = K, Na; M = Fe, V). Both the morphology and electrochemical properties showed a compositional dependence. At potentials >1.5 V vs. Li/Li+, an insertion-type reaction was observed in Na,Fe-jarosite but not in K,Fe-jarosite. Reversible insertion-type reactions were observed in both vanadium jarosites between 1 – 4 V with capacities around 40 - 60 mAh/g. Below 1 V vs. Li/Li+, all four jarosite compounds underwent conversion reactions with capacities ~500 mAh/g for the Fe-jarosites. The electrochemical properties of hydrogen titanium phosphate sulfate, H0.4Ti2(PO4)2.4(SO4)0.6 (HTPS), a new mixed polyanion material with NASICON structure was reported. A capacity of 148 mAh/g corresponding to2 Li+ insertion per formula unit was observed. XRD and XPS were used to characterize the HTPS before and after cycling and to identify the lithium sites. Evaluation of the HTPS in Na-ion cell was also performed, and a discharge capacity of 93 mAh/g was observed. A systematic investigation of the role of the processing steps, such as ball-milling and acid/base etching, on the electrochemical properties of a silicon clathrate compound with nominal composition of Ba8Al16Si30 was performed. According to the transmission electron microscope (TEM), XPS, and electrochemical analysis, very few Li atoms can be electrochemically inserted, but the introduction of disorder through ball-milling resulted in higher capacity, while the oxidation layer made by the acid/base treatment prevented the reation. The electrochemical property of germanium clathrate was also investigated, unlike the silicon clathrate, the germanium one underwent a conversion reaction. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2017

Doctor of Philosophy / Department of Chemistry / Jun Li / Electrical energy storage (EES) is crucial in todays’ society owing to the advances in electric cars, microelectronics, portable electronics and grid storage backup for renewable energy utilization. Lithium ion batteries (LIBs) have dominated the EES market owing to their wide use in portable electronics. Despite the success, low specific capacity and low power rates still need to be addressed to meet the increasing demands. Particularly, the low specific capacity of cathode materials is currently limiting the energy storage capability of LIBs. Vanadium pentoxide (V₂O₅) has been an emerging cathode material owing to its low cost, high electrode potential in lithium-extracted state (up to 4.0 V), and high specific capacities of 294 mAh g⁻¹ (for a 2 Li⁺/V₂O₅ insertion process) and 441 mAh g⁻¹ (for a 3 Li⁺/V₂O₅ insertion process). However, the low electrical conductivities and slow Li⁺ ion diffusion still limit the power rate of V₂O₅. To enhance the power-rate capability we construct two core-shell structures that can achieve stable 2 and 3 Li⁺ insertion at high rates. In the first approach, uniform coaxial V₂O₅ shells are coated onto electrospun carbon nanofiber (CNF) cores via pulsed electrodeposition. The materials analyses confirm that the V₂O₅ shell after 4 hours of thermal annealing at 300 °C is a partially hydrated amorphous structure. SEM and TEM images indicate that the uniform 30 to 50 nm thick V₂O₅ shell forms an intimate interface with the CNF core. Lithium insertion capacities up to 291 and 429 mAh g⁻¹ are achieved in the voltage ranges of 4.0 – 2.0 V and 4.0 – 1.5 V, respectively, which are in good agreement with the theoretical values for 2 and 3 Li⁺/V₂O₅ insertion. Moreover, after 100 cycles, remarkable retention rates of 97% and 70% are obtained for 2 and 3 Li⁺/V₂O₅ insertion, respectively. In the second approach, we implement a three-dimensional (3D) core-shell structure consisting of coaxial V₂O₅ shells sputter-coated on vertically aligned carbon nanofiber (VACNF) cores. The hydrated amorphous microporous structure in the “as-deposited” V₂O₅ shells and the particulated nano-crystalline V₂O₅ structure formed by thermal annealing are compared. The former provides remarkably high capacity of 360 and 547 mAh g⁻¹ in the voltage range of 4.0 – 2.0 V and 4.0 – 1.5 V, respectively, far exceeding the theoretical values for 2 and 3 Li⁺/V₂O₅ insertion, respectively. After 100 cycles of 3 Li⁺/V₂O₅ insertion/extraction at 0.20 A g⁻¹ (~ C/3), ~ 84% of the initial capacity is retained. After thermal annealing, the core-shell structure presents a capacity of 294 and 390 mAh g⁻¹, matching well with the theoretical values for 2 and 3 Li⁺/V₂O₅ insertion. The annealed sample shows further improved stability, with remarkable capacity retention of ~100% and ~88% for 2 and 3 Li⁺/V₂O₅ insertion/extraction. However, due to the high cost of Li. alternative approaches are currently being pursued for large scale production. Sodium ion batteries (SIB) have been at the forefront of this endeavor. Here we investigate the sodium insertion in the hydrate amorphous V₂O₅ using the VACNF core-shell structure. Electrochemical characterization was carried out in the potential ranges of 3.5 – 1.0, 4.0 – 1.5, and 4.0 – 1.0 (vs Na/Na⁺). An insertion capacity of 196 mAh g-1 is achieved in the potential range of 3.5 – 1.0 V (vs Na/Na⁺) at a rate of 250 mA g⁻¹. When the potential window is shifted upwards to 4.0 – 1.5 V (vs Na/Na⁺) an insertion capacity of 145 mAh g⁻¹ is achieved. Moreover, a coulombic efficiency of ~98% is attained at a rate of 1500 mA g⁻¹. To enhance the energy density of the VACNF-V₂O₅ core-shell structures, the potential window is expanded to 4.0 – 1.0 V (vs Na/Na⁺) which achieved an initial insertion capacity of 277 mAh g⁻¹. The results demonstrate that amorphous V₂O₅ could serve as a cathode material in future SIBs.

<p>The single particle model was extended to include electrode and particle volume expansion effects observed in high capacity alloying electrodes. The model was used to predict voltage profiles in sodium ion batteries with tin and tin-phosphide negative electrodes. It was seen that the profiles predicted by the modified model were significantly better than the classical model. A parametric study was done to understand the impact of properties such as particle radius, diffusivity, reaction rate etc on the performance of the electrode. The model was also modified for incorporating particles having a cylindrical morphology. For the same material properties, it was seen that cylindrical particles outperform spherical particles for large L/R values in the cylinder due to the diffusion limitations at low L/R ratios. A lattice spring-based degradation model was used to observe crack formation and creep relaxation within the particle. It was observed that the fraction of broken bonds increases with an increase in strain rate. At low strain rates, it was seen that there was a significant expansion in particle volumes due to creep deformation. This expansion helped release particle stresses subsequently reducing the amount of fracture.</p>

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21783号 / 工博第4600号 / 新制||工||1717(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 安部 武志, 教授 作花 哲夫, 教授 阿部 竜 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

The increased deployment for renewable energy sources to mitigate the climate crisis has accelerated the need to develop efficient energy storage devices. Batteries are at the top of the list of the most in-demand devices in the current decade. Nowadays, research is in full swing to develop a battery that meets the needs of today’s renewable energy systems, which are intermittent by nature. Within the framework of improving the performance of batteries, there are parameters in the composition of the battery that play an important role in its performance: electrode materials, electrolytes, separators, and other factors. The key to battery development is the manufacture of electrode materials with optimal properties. Two-dimensional (2D) materials have led to advances in this field, firstly, using graphite as the anode in lithium-ion batteries (LIBs). However, when using the standard graphite as the anode for sodium-ion batteries (NIBs), the large ionic size and energetic instability of Na+ limit intercalation, resulting in a low storage capacity. Therefore, other 2D materials with large interlayer spacing need to be identified for use as electrodes. In this dissertation, our approach is focus on optimizing anode electrode materials by in situ conversion of 2D materials to obtain hybrid materials. These hybrids materials will synergistically improve the performance of LIBs and NIBs by combining the advantages of individual 2D materials. Starting with converted Ti0.87O2 nanosheets to the TiO2/TiS2 hybrid nanosheets. Then, taking advantage of the properties of MXene, we developed hybrid electrodes based on MXenes by converted V2CTx MXene into V2S3@C@V2S3 heterostructures. Finally, we boosted the redox kinetics and cycling stability of Mo2CTx MXene by using a laser scribing process to construct a multiple-scale Mo2CTx/Mo2C-carbon (LS-Mo2CTx) hybrid material.

This thesis focuses on the development of oxidatively stable cathode and electrolyte materials for sodium-based battery systems. This is primarily achieved through the use of solid-state nuclear magnetic resonance (ssNMR) and pulsed-field gradient (PFG) NMR spectroscopy. ssNMR is used to diagnose the primarily failure mode of the NaOB. It is found through a combined 23Na and 19F study that the main discharge product of the cell, NaO2, oxidizes both the carbon and polyvinylidene fluoride (PVDF) binder of the cathode to produce parasitic Na2CO3 and NaF. In a subsequent study, Ti4O7-coated carbon paper cathodes are implemented in an attempt to stabilize NaO2. The 23Na triple quantum magic angle spinning (3QMAS) and 1H to 23Na dipolar heteronuclear multiple quantum correlation (23Na{1H} D-HMQC) experiments are used to diagnose the failure modes of carbon-coated, and Ti4O7-coated cathodes. It is found that electrochemically formed NaO2 is significantly more stable in Ti4O7-coated cathodes, leading to longer lifetime NaOBs. Oxidatively stable electrolyte materials are also examined. Lithium and sodium bis(trifluoromethansulfonyl)imide (TFSI) in adiponitrile (ADN) electrolytes exhibit extreme oxidative resistance, but are unusable in modern cells due to Al corrosion by TFSI, and spontaneous ADN degradation by Li and Na metal. PFG NMR is used to investigate the transport properties of LiTFSI in ADN as a function of LiTFSI concentration. By measuring the diffusion coefficient of Li+ and TFSI as a function of diffusion time (Δ), diffusional behaviour is encoded as a function of length scale to study the short- and long-range solution structure of the electrolyte. It is found that at high concentrations, LiTFSI in ADN transports Li+ primarily through an ion-hopping mechanism, in contrast to the typical vehicular mechanism observed at low concentrations. This suggests significant structural changes in solution at high concentrations. The NaTFSI in ADN analogue is examined for its electrochemical properties in Na-ion and Na-O2 batteries. It is found that the oxidative resistance of ADN to Na metal is significantly increased at high concentrations, leading to reversible Na deposition and dissolution in cyclic voltammetry (CV) experiments. Linear sweep voltammetry (LSV) and chronoamperometry (CA) experiments on Al current collectors show that Al corrosion by TFSI is similarly suppressed at high concentration. This culminates in high concentration NaTFSI in ADN being able to reversibly intercalate Na3V2(PO4)2F3 (NVPF) cathodes in SIB half-cells for multiple cycles. The knowledge gained from exploring oxidatively stable cathode and electrolyte materials can be used in tandem for the development of a longer lifetime, more oxidatively stable, NaOB in the future. / Thesis / Doctor of Philosophy (PhD) / The continued development of rechargeable batteries is paramount in reducing the world’s reliance on fossil fuels, as they allow for the storage of electrical energy produced by renewable sources. This work primarily examines sodium-based batteries systems, such as the sodium-oxygen battery (NaOB) and sodium-ion battery (SIB), which are possible alternatives to the currently used lithium-ion battery (LIB) system. In order to produce energy, NaOBs produce sodium superoxide (NaO2) during the discharge process, which is formed on the carbon cathode. However, NaO2 is inherently unstable to carbon materials, causing degradation of the battery overtime. Ti4O7 is investigated as a stable coating material in NaOBs, used to coat the carbon cathode to make the system more stable to NaO2 degradation. The degradation processes in NaOBs are characterized by solid state nuclear magnetic resonance (ssNMR) spectroscopy, which uses strong superconducting magnets to probe the magnetic properties of, and consequently identify, the chemical species formed within the battery. It is found that the addition of the Ti4O7 coating inhibits NaO2 degradation, producing longer lifetime NaOBs. Subsequently, both Li-bis(trifluoromethansulfonyl)imide (LiTFSI), and NaTFSI, in adiponitrile (ADN) electrolytes are examined for their use in LIBs and SIBs, respectively. Electrolytes facilitate stable ion transport within the cell, and ADN electrolytes specifically allow for the use of higher voltage cathode materials, which can result in a higher energy density battery. The transport properties of LiTFSI in ADN electrolytes are studied by a pulsed-field gradient (PFG) NMR technique, that allows for the measurement of the rate of ion transport in the electrolyte. It is found that the mechanism of ion transport significantly depends on electrolyte concentration, which suggests significant changes to the electrolyte solution structure at high concentration. The electrochemical ramifications of this are studied for the NaTFSI in ADN electrolyte in SIBs. It is found that the electrolyte becomes substantially more stable at high concentrations, leading to more favourable charging and discharging behaviours when tested in SIBs. The work presented in this thesis illustrates the development of more stable, longer lifetime, batteries over a number of cell chemistries, using a variety of NMR and electrochemical characterization techniques.