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This study sought to improve the performance of Si-based anodes through the use of hierarchically structured electrodes to provide the nanoscale framework needed to accommodate large volume changes while controlling the interfacial area – which affects solid-electrolyte interphase (SEI) formation. To accomplish this, electrodes were fabricated from vertically aligned carbon nanotubes (VACNT) infiltrated with silicon. On the nanoscale, these electrodes allowed us to adjust the surface area, tube diameter, and silicon layer thickness. On the micro-scale, we have the ability to control the electrode thickness and the incorporation of micro-sized features. Treatment of the interfacial area between the electrolyte and the electrode by encapsulating the electrode controls the stabilization and reduction of unstable SEI. Si-VACNT composite electrodes were prepared by first synthesizing VACNTs on Si wafers using photolithography for catalyst patterning, followed by aligned CNT growth. Nano-layers of silicon were then deposited on the aligned carbon nanotubes via LPCVD at 200mTorr and 535°C. A thin copper film was used as the current collector. Electrochemical testing was performed on the electrodes assembled in a CR2025 coin cell with a metallic Li foil as the counter electrode. The impact of the electrode structure on the capacity at various current densities was investigated. Experimental results demonstrated the importance of control over the superficial area between the electrolyte and the electrode on the performance of silicon-based electrodes for next generation lithium ion batteries. In addition, the results show that Si-VACNT height does not limit Li transport for the range of the conditions tested.

In this project, solid sulphur based Li3PS4 electrolytes doped with Li4SiO4 were synthesised using two methods. In method A, a bought β-Li3PS4 electrolyte from Nei Corp was doped with 5 mole per cent Li4SiO4, resulting in a glass-ceramic electrolyte. In method B, the electrolyte was synthesised using 5Li4SiO4-95(75Li2S-25P2S5), resulting in a glassy material. In addition, a reference was synthesised using 75Li2S-25P2S5. Ball milling was the method of choice to dope the glass ceramic electrolyte and synthesise the glassy electrolyte. The dopant Li4SiO4 was synthesised using the chemicals SiO2 and Li2CO3. All samples were analysed using Raman, XPS, XRD, and EIS. In the end, it was found that doping the bought β-Li3PS4electrolyte with Li4SiO4 increased the ionic conductivity. While introducing Li4SiO4 to the glassy electrolyte lowered the ionic conductivity. The increase in ionic conductivity in the glass ceramic electrolyte was partly attributed to the increase in amorphous content, which happened when it was ball-milled and suppressed P-S-P bonds. The decrease in ionic conductivity that happened when doping the glassy material, is most likely caused by residual Li2S that seems unable to react due to the dopant.

Lithium ion batteries (LIBs) are widely used for storing and converting chemical energy into electrical energy. During battery operation, lithium ions move between electrode materials, enabling energy storage. However, aging mechanisms like lithium plating can negatively impact battery performance and lifetime. Lithium plating occurs when lithium ions are reduced to metallic lithium on the graphite electrode. The undesired Li plating in LIBs leads to dendrite formation that may puncture the separator, causing internal short-circuit and ultimately thermal runaway. This study aims to investigate the internal processes of LIBs during charge and discharge. Two analysis methods are employed: online electrochemical mass spectrometry (OEMS) and acoustic emission monitoring (AEM). OEMS is a gas analysis technique that combines electrochemical measurements with mass spectrometry to provide real-time testing of cells. OEMS allows identifying and quantifying gas evolution/consumption of chemical species. AE is a diagnostic tool, offering monitoring the health of LIBs through detection and characterisation of stress waves produced by parasitic mechano-electrochemical events. The results indicates that the formation of SEI thin film layer, generated gases like hydrogen and ethylene, while consuming carbon dioxide. During induced lithium plating, hydrogen and carbon dioxide were consumed, and ethylene gas was produced, due to new SEI film formation process. The acoustic emission analysis indicated that lithium plating was an active process, whereas SEI formation was less AE active. Further research is needed to understand the relationships and significance of these processes for battery performance and safety. Overall, this study highlighted the importance of investigating aging mechanisms in LIBs to enhance their performance and longevity. By combining OEMS and AE, it was possible to analyse the batteries behaviour during cycling. The evolution of gas and acoustic signals provided insights into the reactions and processes occurring inside the battery during cycling.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24108号 / 工博第5030号 / 新制||工||1785(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

An investigation of electrochemical storage device materials has been undertaken in four parts. The bulk and interfacial resistance of Na+ beta-alumina tubes were separated using a galvanostatic charge-discharge method. Sodium silicide was characterized to better understand its synthesis. BiMn2O5 was produced using a sol-gel method and tested for pseudocapacity. Different lithium ion anode and cathode materials were deposited using a new electrophoretic deposition method. A novel galvanostatic charge-discharge method was developed for the determination of bulk and interface resistance in Na+ beta-alumina solid electrolytes [BASE]. Dense and duplex BASE tubes were tested by varying the exposed surface area. The results of dense BASE tube pairs were used to determine the bulk and interfacial resistance components, while duplex BASE tubes were tested to determine the reduction in interfacial resistance. It was found that duplex tubes had reduced the interfacial resistance by 75%, when compared to a uniformly dense electrolyte. Sodium silicide was characterized using various methods to better understand the phase and the Na-Si phase diagram. EMF experiments using Na+ BASE tubes was used to determine the activity in the silicon rich region of the phase diagram, which showed a sodium activity of 0.5 at 550°C. TGA/DSC was used to determine phase transformation temperatures, as well as the heat of formation for NaSi, which was recorded to be below 1 kJ mol-1. A sol-gel precipitation method was used to produce fine BiMn2O5 powders used for supercapacitors. The powders resulting from a consistent method were tested for pseudocapacitance using bulk and thin film electrodes. Bulk electrodes had a gravimetric capacitance of 10 F g-1, while thin film electrodes only reached 2.6 F g-1. Lithium ion battery anode (Li4Ti5O12) and cathode (LiFePO4, LiMn2O4, LiMn1.5Ni0.5O4) materials were electrophoretically deposited with the assistance of PAZO-Na and CMC-Na. Cathodes were successfully deposited on aluminium substrates, and were tested in the potential window 2 – 4.3 V. The LiFePO4 cathodes showed capacity of 146.7 mAh g-1 at C/10, while showing capacity retention of 103% after 50 cycles. / Thesis / Doctor of Philosophy (PhD) / The goal of this work is to examine materials used in different types of electrochemical storage devices. The modification of resistive properties of β-alumina electrolytes are examined for use in high temperature sodium batteries. Electrophoretic deposition methods are used to rapidly make thin electrodes for lithium ion batteries and supercapacitors. The stoichiometric compound NaSi, a potentially safer and greener method of producing hydrogen gas, is characterized for a better understanding of its properties, and therefore production.

Silicon (Si) has been considered as a promising negative electrode material for lithium ion batteries (LIBs) because of its high theoretical capacity, low discharge voltage, and low cost. However, the utilization of Si electrode has been hampered by problems such as slow ionic transport, large stress/strain generation, and unstable solid electrolyte interphase (SEI). These problems severely influence the performance and cycle life of Si electrodes. In general, ionic conduction determines the rate performance of the electrode, while electron leakage through the SEI causes electrolyte decomposition and, thus, causes capacity loss. The goal of this thesis research is to design Si electrodes with high current efficiency and durability through a fundamental understanding of the ionic and electronic conduction in Si and its SEI. Multi-scale physical and chemical processes occur in the electrode during charging and discharging. This thesis, thus, focuses on multi-scale modeling, including developing new methods, to help understand these coupled physical and chemical processes. For example, we developed a new method based on ab initio molecular dynamics to study the effects of stress/strain on Li ion transport in amorphous lithiated Si electrodes. This method not only quantitatively shows the effect of stress on ionic transport in amorphous materials, but also uncovers the underlying atomistic mechanisms. However, the origin of ionic conduction in the inorganic components in SEI is different from that in the amorphous Si electrode. To tackle this problem, we developed a model by separating the problem into two scales: 1) atomistic scale: defect physics and transport in individual SEI components with consideration of the environment, e.g., LiF in equilibrium with Si electrode; 2) mesoscopic scale: defect distribution near the heterogeneous interface based on a space charge model. In addition, to help design better artificial SEI, we further demonstrated a theoretical design of multicomponent SEIs by utilizing the synergetic effect found in the natural SEI. We show that the electrical conduction can be optimized by varying the grain size and volume fraction of two phases in the artificial multicomponent SEI.

This dissertation is focus on the study of solid-electrolyte interphases (SEIs) on advanced lithium ion battery (LIB) anodes. The purposes of this dissertation are to a) develop a methodology to study the properties of SEIs; and b) provide guidelines for designing engineered SEIs. The general knowledge gained through this research will be beneficial for the entire battery research community.

Les microbatteries sont des microsources d’énergie adaptées à l’alimentation des microsystèmes tels que l’horloge à temps réel des téléphones portables, les étiquettes intelligentes RFID…. Pour pouvoir être considéré comme un composant classique de la microélectronique, la microbatterie doit être compatible avec le processus de soudure de type solder-reflow qui atteint une température de 260 °C pendant quelques secondes. Au cours de cette thèse, nous nous sommes focalisés sur l’étude de couches minces de LiPON (oxynitrure de phosphate de lithium) utilisé comme électrolyte solide qui est le matériau limitant pour une application à basse température en établissant des relations entre sa composition, sa structure et ses performances électriques. Ayant observé une baisse des performances après traitement thermique, nous avons proposé un matériau présentant une meilleure stabilité. Nous avons également étudié la compatibilité des autres couches ainsi que l’empilement complet de la microbatterie vis-à-vis du solder-reflow. / Microbatteries are energy sources well-adapted to power microsystems such as the real time clock of mobile phones, smart tags RFID. To be considered as a microelectronic component, the microbattery must be compatible with the solder-reflow process which reaches a temperature of 260 °C during few seconds. During this Ph-D, various thin films of LiPON (lithium phosphate oxynitride) used as amorphous solid electrolyte have been prepared by sputtering. As this material presents limited performances for an application of the microbattery at low temperature, we have investigated the influence of its composition and local structure on its electrical performances. In addition, a decrease of its performances has been noticed after solder-reflow. In this work, we have proposed a new material, much more thermally stable. Finally, we have studied the compatibility of other active layers as well as the all-solid-state microbattery towards the solder-reflow.