Thesis (Ph.D.) -- University of Adelaide, Dept. of Physics, 1978.

Different types of alumina containing coatings were made on lithiumand copper in the purpose to mechanically hinder the growth ofdendrites. Lithium, coated with polymer-alumina composites wereplaced in symmetric cells for in situ studies by a light microscope.The coatings did not block the dendrites, but they did change thegrowth rate and morphology of them, probably throw both chemicalinteractions and changes in ion transportation. Also the stability ofcapacity were tested for the same coatings, the result showed abigger capacity drop for cells containing coated lithium versus cellswithout coatings.Attempted alumina coatings were also made by a solgel technique, bydirect reaction with the compound trimethylaluminium and with analumina containing acetonitrile solution.The theses also includes a study of the stability of lithium inadiponitrile. A higher amount of LiTFSI salt in adiponitrile could bythis study be reported to inhibit the dissolution of lithium that wasseen for lower salt concentrations. The dissolution appeared when thesolution was used as an electrolyte in a symmetric lithium cell. Somedifferences could be seen when the lithium surface were studied byXPS after interaction with high, low and zero concentration LiTFSI.Both the XPS studies and the absences of lithium dissolutionindicates that a more or less stable SEI had been formed.

Since their commercialization in 1990, the electrodes of the lithium-ion battery have remained fundamentally the same. While energy density improvements have come from reducing the cell packaging, higher capacity electrodes are needed to continue this trend. A lithium metal anode, where the negative electrode half reaction is the plating and stripping of metallic lithium, is explored as an alternative to current graphite anodes. The specific capacity of the lithium metal anode is over ten times that of the graphite anode, making it a serious candidate to further improve the energy density of lithium batteries. Electrodeposited lithium metal forms dendrites, sharp needles that can grow across the separator and short circuit the battery. Thus, a chief goal is to alter lithium’s plating morphology. This was achieved in two separate ionic liquid electrolytes by co-depositing lithium with sodium. The co-deposited sodium is thought to block dendritic sites, leading to a granular deposit. A nucleation study confirmed that metal deposits from the ionic liquid electrolyte containing sodium, prevented dendritic growth from nucleation on, and not after dendrites had already grown. A model based on the geometry of the nuclei was used to gain insight into the effect of the solid electrolyte interface (SEI) that forms on freshly deposited lithium metal. In addition to sodium, the effect of alkaline earth metals on the lithium deposit morphology was also explored. While these metals did not deposit from the ionic liquid electrolyte, their addition also resulted in granular, dendrite free, deposits. The alkaline earth additives generally increased the overpotential for nucleating on the substrate and lowered the current density achievable. Strontium and barium showed the least of these negative effects while still providing a dendrite free deposit. A second hurdle for lithium metal anodes is the instability between the electrolyte and lithium metal. A protective SEI layer that prevents undesired side reactions is difficult to form because of the large volume change associated with cycling. Formation of a better SEI on lithium metal was attempted through the addition vinylene carbonate, which greatly improved the coulombic efficiency of lithium metal plating and stripping. The effect of gases, such as oxygen, nitrogen and carbon dioxide, on the SEI layer was also investigated. It was found that the presence of nitrogen and oxygen improved the coulombic efficiency by facilitating a thinner SEI layer. This work presents attempts at improving the lithium metal anode both by increasing the coulombic efficiency of the redox process and by eliminating dendrite growth. The coulombic efficiency was improved through the bubbling of gases and addition of organic additives but work remains to increase this value further. Dendritic growth, which poses a safety hazard, was completely eliminated by two methods: 1) co-deposition and 2) adsorption of a foreign metal. Both methods could potentially be applied to different electrolytes, making them promising methods for preventing dendritic growth in future lithium metal anodes.

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全文ファイル差し替え（2021.07.28） / 京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第22132号 / エネ博第400号 / 新制||エネ||77(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 萩原 理加, 教授 佐川 尚, 教授 野平 俊之 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

The shortage of energy sources and the global climate change crisis have become critical issues. Solving these problems with clean and sustainable energy sources (solar, wind, tidal, and so on) is a promising solution. In this regard, energy storage techniques need to be implemented to tackle with the intermittent nature of the sustainable energies. Among the next-generation energy storage systems, lithium sulfur batteries has gained prominence due to the low cost, high theoretical specific-capacity of sulfur. Extensive research has been conducted on this battery system. Nevertheless, several issues including the “shuttle effect” and the growth of lithium dendrites still exist, which could cause rapid capacity loss and safety hazards. Several methods are proposed to tackle the challenges in this dissertation, including cathode engineering, interlayer design, and lithium metal anode protection. An asymmetric cathode structure is first developed by a non-solvent induced phase separation (NIPS) method. The asymmetric cathode comprises a nanoporous matrix and ultrathin and dense top layer. The top-layer is a desired barrier to block polysulfides transport, while the sublayer threaded with cationic networks facilitate Li-ions transport and sulfur conversions. In addition, a conformal and ultrathin microporous membrane is electrodeposited on the whole surface of the cathode by an electropolymerization method. This strategy creates a close system, which greatly blocks the LiPS leakage and improves the sulfur utilization. A polycarbazole-type interlayer is deposited on the polypropylene (PP) separator via an electropolymerization method. This interlayer is ultrathin, continuous, and microporous, which defines the critical properties of an ideal interlayer that is required for advanced Li–S batteries. Meanwhile, a self-assembled 2D MXene based interlayer was prepared to offer abundant porosity, dual absorption sites, and desirable electrical conductivity for Li-ions transport and polysulfides conversions. A new 2D COF-on-MXene heterostructures is prepared as the lithium anode host. The 2D heterostructures has hierarchical porosity, conductive frameworks, and lithiophilic sites. When utilized as a lithium host, the MXene@COF host can efficiently regulate the Li+ diffusion, and reduce the nucleation and deposition overpotential, which results in a dendrite-free and safer Li–S battery.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第17887号 / 工博第3796号 / 新制||工||1581(附属図書館) / 30707 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 田中 功, 教授 酒井 明, 教授 邑瀬 邦明 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

The pursuit of reliable and high-performance batteries has fueled extensive research into new battery chemistries and materials, aiming to enhance the current lithium-ion battery technologies in terms of energy density and safety. Among the potential advancements, solid-state batteries (SSBs) have captured significant attention as the next-generation energy storage technology. One key factor contributing to their appeal is the utilization of solid-state electrolytes (SSEs) with a wide electrochemical stability window (ESW), making SSBs compatible with high-voltage cathodes. The energy density of SSBs can be further improved by employing the “holy-grail” anode, Li-metal, which boasts the lowest working voltage (-3.04 V vs. Li+/Li) and an ultrahigh theoretical capacity (3860 mAh g−1). Consequently, these batteries are referred to as lithium metal batteries (LMBs). However, realizing the full potential of LMBs presents formidable challenge, including the low ionic conductivity of current SSEs, large interfacial resistance between SSE and electrodes, uncontrollable interfacial reactions, and the growth of Li dendrites.  Typically, SSEs can be categorized into three types. Among these, solid composite electrolytes (SCEs) are considered the most promising choice for solid-state LMBs due to their combination of high ionic conductivity and excellent mechanical strength from inorganic solid electrolytes (ISEs) and the flexibility and good interface compatibility provided by solid polymer electrolytes (SPEs). Polymeric ionic liquids (PolyILs), which contain both ionic liquid-like moieties and polymer frameworks, have emerged as highly attractive alternatives to traditional polymers in SCEs.  The overall objective of this thesis was to develop PolyIL-based SCEs with enhanced ionic conductivity, wide ESW, high Li+ transference number, and reduced electrodes/electrolyte interface resistance. The main progress achieved in this thesis is as follows: 1. We selected three F-based Li-salts to prepare SPEs using poly(ethylene oxide) and polyimide. The investigation focused on assessing the impact of molecular size, F content, and chemical structures (F-connecting bonds) of these Li-salts. Additionally, we aimed to uncover the formation process of LiF in the solid electrolyte interphase (SEI). The result revealed that the F-connecting bond plays a more significant role than the molecular size and F element content, resulting in slightly better cell performance using LiPFSI compared to LiTFSI and substantially better performance compared to LiFSI. The preferential breakage of bonds in LiPFSI was found to be related to its position to Li anode. Consequently, we proposed the LiPFSI reduction mechanism based on these findings. 2. Using the template method, we synthesized a monolayer SCE with enhanced Li+ transference number and high ionic conductivity. In this study, boron nitride (BN) nanosheets with a high specific surface area and richly porous structure were employed as inert inorganic filler. These BN nanosheets played a crucial role in homogenizing the Li+ flux and facilitating the Li+ transmission to suppress Li dendrite growth. When integrated into a LiFePO4//Li cell with the optimized SCE, the assembled battery demonstrated remarkable cycling performance.  3. A monolayer GSCE with multifunctionality was synthesized via a natural sedimentation and subsequent UV-curing polymerization technique. This innovative method capitalizes on intrinsic gravity, allowing for the integration of multiple functions within a single layer, thereby eliminating the additional interlayer resistance. The developed GSCE provides an optimum Li+ transportation path and enhanced Li+ transference number, leading to an enhanced ionic conductivity and a long cycle life of Li//Li cells and SSLMBs. Compared with the monolayer uniform SCEs, the gradient structure also alleviates the uncoordinated thermal expansion between fillers and PolyIL, avoiding increased stress during the cycle and battery capacity fade.

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