京都大学 / 新制・論文博士 / 博士(工学) / 乙第13408号 / 論工博第4194号 / 新制||工||1762(附属図書館) / (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2項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

<p>Paper-based flexible devices represent a new frontier in electronics technology. The research has focused on the fabrication of the lightweight, and flexible paper-based lithium ion batteries. A lithium ion battery relies on the interplay of multiple components. These components themselves, as well as the processes used to create them, need to be adjusted and modified in order to achieve a fully flexible lithium ion battery. These components include the electrode current collector, active material, and electrolyte. By modifying these components to be fully flexible and resistant to damages caused by deformation, a fully flexible battery can be achieved.</p> <p> </p> <p>Herein, the paper-based platform utilized is key to provide flexibility for the battery components. The goal of this work not only focused on the creation of a paper-based flexible battery to be used as an integrable energy storage system for flexible devices, but also on developing methodologies and processes that can advance the emerging area of paper-based electronics, where different functional units must be fabricated within a single paper substrate. The key to make effective paper-based batteries, is to achieve a highly conductive paper structure as the base. In this work, conductive nanomaterials including carbon nanotubes (CNT) and graphene were used to fabricate conductive paper, where wood microfibers were coated with layers of these nanomaterials via layer-by-layer nanoassembly. These fibers were then combined into paper sheets. The resulting paper offers a conductive and porous base for electronic devices that utilized only small quantities of CNT or reduced graphene oxide (rGO) to provide length resistances of 468 Ω/cm and 74.6 Ω/cm, respectively for each fabricated conductive paper. </p> <p> </p> <p>Flexible lithium ion batteries were then made by using CNT paper-based electrodes and a solid polymer gel electrolyte. The electrodes were made by deposition of lithium active materials over the conductive paper and where shown to be flexible, durable, and light weight. With respect to the electrolyte, a new type of gel electrolyte based on PVDF-HFP was fabricated to overcome problems related to the use of liquid electrolytes in flexible batteries. This gel, which provides a high electrolyte uptake (450% by weight), was made by infusing both liquid and ceramic electrolytes inside a polymer gel structure and demonstrated conductivity up to 10^-4 S/cm. The paper-based battery developed with these new materials has a comparable capacity to commercial batteries and represents a flexible and light weight alternative. The use of ultra-high capacity lithium compounds as cathode materials, such as vanadium pentoxide (with theoretical capacities of 440 mAh/g) in conjunction with rGO-paper as a stand-alone electrode (with a reversible capacity 546 mAh/g) were also explored and results will be discussed. </p> <p> </p> <p>This research has led to the development of a novel method of making a fully flexible lithium ion batteries, using paper-based current collectors, leak proof polymer gel electrolytes and ultra-high capacity lithium ion active materials. Thus, flexible high conductive paper-based current collectors, polymer-gel electrolytes, vanadium based ultra-high capacity cathode electrodes, and graphene-based stand-alone paper-based anodes have been developed and tested.</p> <p> </p>

The master's thesis is devoted to the comparison of different types of lithium-ion batteries. Primarily, an introduction to electrochemical power sources and their division is described. Furthermore, the thesis deals only with lithium-ion batteries. In the theoretical part, the chapters discuss the history, the principle of operation and a detailed description of the main battery parts, including used materials. A comparison of commercially available lithium-ion cells with each other as well as with other types of batteries is also included in the theoretical part. The practical part deals with the cyclinf of lithium-ion cells and subsequent evaluation of the effect of temperature on the capacitance and current characteristics of these lithium-ion batteries.

This thesis deals with the preparation and characterization of electrode materials for Li-ion batteries based on elemental sulfur. The theoretical part is focused on the characteristics of Li-ion batteries, electrochemical reactions, the process of electrochemical lithiation of sulfur and solubility properties of intermediate polysulfides. The practical part of the thesis deals with the preparation of cathode materials for Li-ion cells with an active substance in the form of elemental sulfur. The prepared electrodes were investigated using cyclic voltammetry and galvanostatic cycling. Physical characterization by SEM and XRD was provided.

In this thesis, the diffusion of lithium was studied on boron-doped diamond (BDD) as a potential anode material in lithium ion batteries (LIB). The initial interaction between deposited lithium and BDD thin films was studied using X-ray Photoelectron Spectroscopy (XPS). Diffusion is directly linked to reactions between lithium and carbon atoms in the BDD-lithium interface. By measuring binding energies of core-electrons of carbon and lithium before and after deposition, these reactions can be analyzed. Scanning Electron Microscopy (SEM) was used to study the BDD surface and the behaviour of deposited lithium. Experiments show that a chemical interaction occurs between lithium and carbon atoms in the surfacelayers of the BDD. The diffusion of lithium is discussed from spectroscopic data and suggests that surface diffusion is occurring and no proof of bulk diffusion was found. The results do not exclude bulk diffusion in later states but it was not found in the initial interaction at the interface after depositing lithium. SEM images show that lithium clusters in the nanometer range are formed on the BDD surface. The results of this study give insights in the initial diffusion behaviour of lithium at the BDD interface and possible following events are discussed.

<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>

The research is mainly motivated by the abundance of sodium and the larger amount of sodium compounds in comparison with lithium.

In the presentation, focus will be on some interesting effects related to lithium insertion and deinsertion, recently identified in industrially used metal oxide electrodes like NCA, Li(Ni,Co,Al)O2 and LFP, LiFePO4.

This work developed a novel experiment in order to determine the operational effects on a Lithium-ion battery (LIB) when a test resulting in non-catastrophic damage is performed. Accepted industry standards were used as a basis to develop a nail penetration test that would puncture a cell approximately halfway through during normal cycling at a rate of 1C, then allow the cell to continue cycling to determine how its operation was affected. The cells under test continued cycling after the punctures, showing that the experiment would be able to provide useful information on the topic. The experiment was found to be successful in simulating the operation of a cell in an abusive environment, such as those seen in electric vehicles and aerospace applications.<div><br></div><div>The results of these experiments showed that a sharp increase in temperature is observed immediately after the puncture, similar to cells that underwent tests with full penetrations. The temperatures then slowly decreased during the first few cycles after the puncture as the generated heat was dissipated through convection. The experiments also showed that it is possible for a LIB under test to continue operating for a short time after being punctured. However, the capacity and useful life of the cells were greatly reduced. The initial capacity of each cell decreased by approximately 11% after the initial impact, then continued decreasing at an accelerated rate during the ensuing cycling. The lifetime of the cells was also greatly reduced, with each cell reaching its end of life within approximately 15-75 cycles after the punctures. An analysis of the incremental capacity curves of the cells indicated that accelerated aging occurred due to both a loss of active material and a loss of lithium inventory. The information gained from the experiments gives insight into the operation of cells that experience abusive environments and will be useful in designing improved control systems, as well as promoting the development of more robust testing and safety standards for different types of cells.<br></div>

The purpose of this survey has been to test and analyse the behaviour of battery systems mixing parallel strings of lithium and lead acid. The underlying theory of why batteries of different chemistries behaves together was investigated in order to understand the resulting tests. Several tests were made with different products, loads and chargers in order to confirm this theory and to discover cases where the system works good and where it works bad. Based on this understanding a script was made in order to find a point of the least annual cost. Annual cost was then compared with systems of Lead acid only and Lithium only. The final goal for the script was so that a salesman can input known parameters for a backup site. Script is then adding a small Lithium battery in parallel with a fixed Lead acid battery and, increasing Lithium in size and estimating depth of discharge for Lithium and Lead acid at each step, until desired breakpoint. A point of minimum system cost together with Li size is then represented together with the recommended current limits. / Avsikten med detta exjobb har varit att testa och analysera beteendet av batteri-system där man blandar litium och bly parallellt. Den underliggande teorin om varför batterier av olika kemier beter sig på ett visst sätt tillsammans undersöktes för att få en förståelse för testresultaten. Ett flertal tester gjordes med olika batterier, laster och laddare för att verifiera teorin och för att upptäcka fall där systemet funkar bra och där det funkar dåligt. Baserat på denna förståelse gjordes ett script med avsikten att hitta en punkt med en lägsta årlig kostnad. Denna kostnad jämfördes sedan med system bestående av enbart bly samt enbart litium. Det slutgiltiga målet med scriptet var att en säljare ska kunna fylla i kända parametrar för en viss telekom-anläggning. Scriptet lägger sedan till ett litet Litium-batteri parallellt med ett konstant bly-batteri. För att sedan öka på Litium i storlek och uppskatta urladdningsdjupet för Litium och bly vid varje steg, tills dess att Li har samma storlek som bly. En punkt för minsta kostnaden presenteras sedan tillsammans med optimal storlek av Litium samt rekommenderade max-strömmar.