京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第17916号 / エネ博第288号 / 新制||エネ||60(附属図書館) / 30736 / 京都大学大学院エネルギー科学研究科エネルギー変換科学専攻 / (主査)教授 小西 哲之, 教授 星出 敏彦, 教授 木村 晃彦 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

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In this study we develop a computational approach to the solution of an inverse modelling problem concerning the material properties of electrolytes used in Lithium-ion batteries. The dependence of the diffusion coefficient and the transference number on the concentration of Lithium ions is reconstructed based on the concentration data obtained from an in-situ NMR imaging experiment. This experiment is modelled by a 1D time-dependent PDE describing the evolution of the concentration of Lithium ions with prescribed initial concentration and fluxes at the boundary. The material properties that appear in this model are reconstructed by solving a variational optimization problem in which the least-square error between the experimental and simulated concentration values is minimized. This optimization problem is solved using an innovative gradient-based method in which the gradients are obtained with adjoint analysis. In the thesis we develop and validate a computational framework for this reconstruction problem. Reconstructed material properties are presented for a lab-manufactured and a commercial battery electrolyte providing insights which complement available experimental results. / Thesis / Master of Science (MSc)

Electrode microstructure influences ionic transport and electronic transport and is a key factor that affects lithium-ion battery performance. Non-uniform microstructure or heterogeneity in battery electrodes has long been observed and leads to non-uniform transport properties. This work provides a better understanding of in-plane heterogeneity at millimeter length scale and through-plane heterogeneity at micrometer length scale, through a combination of experiment and modeling. The first part of this work develops the aperture probe technique, which is an experimental method and associated model to locally estimate ionic transport, represented by MacMullin number, in the electrode. By generating contour maps of MacMullin number, the in-plane variation of ionic transport is visualized in the electrodes. The local ionic transport measurement technique is validated by comparing with another measurement technique and showing an agreement between the results obtained from the two techniques. The second part of this work focuses on characterizing dual-layer anodes that consist of two layers of coating with distinctly different microstructures. The aperture probe technique was adapted to determine the MacMullin numbers in the two layers separately. The method was validated by a series of virtual experiments and by comparing in one case to an electrode film that was delaminated from the current collector and experimentally sampled from both sides. Because both the electronic transport and the ionic transport are found to be related with the electrode microstructure, it is of interest to understand how these two transport properties relate to each other. The local electronic conductivity and MacMullin number of several commercial-grade electrodes were mapped. The correlation between the two transport properties is distinct for each electrode and significant at length scales larger than about 6 mm. The last part of this work investigates how heterogeneity of ionic transport affects the cycling performance of a lithium-ion cell. A localized MacMullin number measurement is made to characterize the ionic transport heterogeneity of electrodes prior to cycling. Then synchrotron-based X-ray diffraction is applied to analyze the heterogeneity in state of lithiation after high-rate cycling. When comparing the ionic transport map and the state-of-charge map, no strong correlation is observed. While this experiment was inconclusive, it suggests that other factors are more responsible for spatial variations in state of lithiation.

Rechargeable lithium ion batteries are common materials in everyday applications. The most frequently used cathode material, LiCoO2, provides high energy density and stable charge/discharge performance. However, LiCoO2 is toxic and relatively expensive, therefore, other alternatives are being sought after in the development of battery materials, such as LiMn0.33Ni0.33Co0.33O2 (identified commonly as 333 compound). The 333 compound is now popular due to its comparable performance with LiCoO2, lower price, enhanced stability, and more environmentally friendly characteristics. In addition, Li1.2Mn0.54Ni0.13Co0.13O2 (HENMC) is still on the stage of testing and it attracts wide attention due to its higher rechargeable capacity and thermal stability. However, there are still challenges confronted: cycle stability and low rate capability. In order to verify all the roles played by different elements shown in NMC materials and explore the corresponding performance with different formula units, compositional analysis is needed. ICP-MS (inductively coupled plasma mass spectrometry) can provide bulk compositional information and has been used in recent work, giving a general idea of the composition of NMC materials. However, compositional inhomogeneity analysis has usually been neglected in these studies. Therefore, the objective of this work was to explore this variation in composition locally with higher spatial resolution, at the NMC particle level. This work was carried out through the use of scanning electron microscopy – energy dispersive spectroscopy (SEM-EDS) and Auger electron spectroscopy (AES). Furthermore, nano-scale quantitative analysis was done with transmission electron microscopy – energy dispersive spectroscopy (TEM-EDS). Moreover, an optimal approach and procedure of compositional analysis by using EDS and AES was explored with proper standards and operation conditions to provide consistent and stable results. The optimal quantification method was applied to investigate the compositions of 333 compound before and after ball milling and HENMC specimen before and after cycling. The results support the structural changes and in turn the electrochemical performance of the battery material. In the 333 compound, the electrochemical performance of the battery was deteriorated due to ball milling, during which Zr was introduced and particles were more compact. In HENMC, during cycling, the Mn distribution was homogeneous at the beginning, then inhomogeneous and homogeneous again, supporting the hypothesis of the transformation of phases: formation of spinel phase and potential SEI layer. In-depth structural analysis of different NMC materials has been reported previously by other groups. However, the structural effects due to cycling, within particles still needs investigation. Therefore, X-ray diffraction (XRD) was used to investigate the bulk material crystalline structure. Local nano-scale level structural variations amongst different isolated primary particles were investigated by the electron diffraction pattern based on TEM. The 333 compound and HENMC cycling was examined before and after cycling. After cycling, in the 333 compound, the O1 phase domains with P-3m1 space group appear inside the O3 phase with R-3m lattice. With more cycling, more domains appear. For HENMC, the original pristine samples exhibit the rhombohedral and monoclinic phases. After cycling, more and more spinel phase appear. Finally, after 100 cycles, we observe evidence of the potential solid electrolyte interphase (SEI) formation. In all, all the results above support the phase changes of 333 compound and HENMC. More investigations are needed to understand the degradation process of both compounds. / Thesis / Master of Materials Science and Engineering (MMatSE)

<p> This thesis deals with the changes, in the response of a Ge(Li) gamma ray detector, arising from damage caused by its exposure to high energy neutrons. The phenomenon of charge trapping is considered and included in a model explaining the collection of electron-hole pairs in a Ge(Li) detector. From this model a response function for the output of the detector is obtained and then applied to a description of the changes in FWHM of pulse height spectra peaks with energy and neutron irradiation.</p> <p> Described are experiments in which three detectors were exposed to fast neutrons and their changing response was related to the response function. Finally the number of damage centres produced by the neutrons is discussed.</p> / Thesis / Master of Science (MSc)

<p> This thesis deals with the theory and application of semi-conductor detectors to timing measurements. The theory section discusses the charge collection times in the coaxial detector. The third chapter describes the experimental procedure for the γ-γ coincidence work, and the fourth part reports the results of studies of the timing characteristics of the coaxial detector.</p> / Thesis / Master of Science (MSc)

Lithium ion batteries (LIBs) are crucial for modern electronics and electric vehicles (EV). However,their electrochemical performance is facing challenges at low temperatures (e.g ≤ 0 °C) due to reducedLi+ kinetics and increased charge-transfer resistance. Given the growing dependence on LIBs for bothelectronics and EVs, especially in cold environments, it is imperative to address the low-temperaturelimitations. Thus, improving the low-temperature performance of LIBs is essential for the broaderadoption and further advancement of LIBs. To address these challenges, this thesis demonstrates thatsignificant improvement of electrochemical performance at low temperatures can be achieved by in-corporating Lithium difluoro(oxalato)borate (LiDFOB) as an additive into the baseline electrolyte forthe Li(Ni0.8Mn0.1Co0.1)O2(NMC811)∥Li cell.At a low temperature of -20 °C, the NMC811∥Li cell with the electrolyte containing 4 wt% LiDFOBexhibited an impressive discharge capacity of 125 mAh/g at 0.1C (1C = 2.0 mAh cm−2), representingabout 61.6% of the capacity delivered at 20 °C. In contrast, the cell with the baseline electrolyte de-livered negligible discharge capacity under the same conditions. This result emphasizes the functionsof LiDFOB as an electrolyte additive in enhancing the low-temperature performance of NMC811∥Licells. This work reveals the kinetics bottleneck of Li+ transport during charge/discharge processes atlow temperatures can be mitigated by tuning cathode-electrolyte interphase (CEI) through introducingadditive into the baseline electrolyte.To substantiate these findings, Electrochemical Impedance Spectroscopy (EIS) was employed to re-veal the significant decrease of interface resistance resulting from the addition of LiDFOB into thebase electrolyte. X-ray Photoelectron Spectroscopy (XPS) further confirmed the benefits of LiDFOB,indicating that a B-rich, more conductive and thinner CEI formed on the NMC811 cathode induced byLiDFOB. The results indicate that the inclusion of LiDFOB in the baseline electrolyte is advantageousin tuning CEI at the cathode for reducing charge-transfer resistance and enhancing electrochemicalperformance.In conclusion, the tuned CEI induced by LiDFOB additive plays an important role in improving thelow-temperature performance of the NMC811∥Li cells. This improvement in the capacity delivery at-20 °C can be attributed to the formation of a highly conductive and uniform and thinner CEI layer,which in turn facilitates reduced charge-transfer resistance at low temperatures. This work sheds newlight on the electrolyte design with additives to develop high-performance LIBs operating at extremeconditions.2

If you buy a new electric car today it will take on average about ten years for you to start saving money compared to just continue driving your old gasoline car. It will also take about 4 years until you start saving carbon dioxide emissions, both of this is because of new production costs and emissions. As the EU has banned producing new fossil fuel cars from 2035, it’s just a question of time before the power train in our cars will be electric. This rapid transition will lead to the older generation gasoline cars left by the road, with still usable chassis. This calls for a solution that uses this chassis but swaps out its power train for an electric one, reducing the initial cost and emission to drive electric. But is it that easy? In this mission, we take that technical question into our hands and convert a Swedish classic Volvo 340 from 1979 and give it an electric power train from 2022. We provide a detailed theory about the technology, a guide in choosing the right components, and the legal build requirements to pass the inspection. The conversion is done in an ordinary garage with standard tools and a welder. Using a small power-train with a maximum power of 30kW (40hp) and a battery size of 20kWh gave us a car with a maximum speed of 110km/h and a range of 150km. The project costed a total of 60 000 kronor, including the registration process. The technical legality and registration process went smoothly thanks to the Organisation SFRO (Sveriges fordonsbyggares riksorganisation) which takes care of the technical inspection and handles the paperwork. After one year and 10 000 km of driving and collecting data, we estimate that transitioning from gasoline to electric via a conversion compared to a new electric car reduces the economical investment return time from 10 to 2 years. And saves 8 tons of CO2. The battery used is secondhand. The second-hand market of electric car batteries, mostly from crashed or defective cars is growing and is estimated to be enough to convert the majority of old gasoline cars that are in good condition. The life length of second hand batteries in conversion is estimated to be equal to the rest of the chassis, due to the lower power requirements in conversion builds. We see that this idea has potential on a larger scale due to satisfying the criteria: Enough low complexity to do a conversion (if using common car models), lower cost and CO2 emissions then other options, supply for batteries exists, donor cars exist with chassis in good condition, market size is big enough and it’s legal to modify your car in Sweden and a few other countries. / Det är bara en tidsfråga innan drivlinan i våra bilar kommer att vara elektrisk, eftersom EU har lagt ett förbud mot att producera nya fossilbränslebilar från 2035. Men det är inte det enda trycket på förändring eftersom även bensinpriserna fortsätter att öka. En mycket hög efterfrågan förväntas på elbilar. Men för de flesta är det inte ett ekonomiskt alternativ att köpa en ny elbil, även om användandet är billigare tar det cirka 10 år innan du börjar se besparingar. Även produktionen av nya elbilar släpper ut koldioxid, motsvarande cirka 4 års körning av en bensinbil. Den snabba övergången kommer också att leda till att den äldre generationens bensinbilar skrotas, med fortfarande användbara chassi. Detta kallar på en lösning som använder dessa chassin men byter ut sin drivlinan till en elektrisk, vilket minskar den initiala kostnaden för att köra elbil samtidigt som man sparar in utsläppen från en ny produktion. Men är det verkligen så lätt? Vi tar vi frågan i våra händer och konverterar en svensk klassiker, en Volvo 340 från 1979 och ger den en drivlina från 2022. Vi ger en detaljerad teori om tekniken, en guide för att välja rätt komponenter och lagliga byggkrav för att klara besiktningen. Konverteringen görs i ett vanligt garage med standardverktyg och en svets. Ett år och tusen mil senare av körning och insamling av data uppskattar vi att en övergång från bensin till el via en konvertering jämfört med en ny elbil minskar den ekonomiska avkastningstiden för investeringen från 10 till 2 år. Och sparar 8 ton koldioxid. Batteriet som används är begagnat. Andrahandsmarknaden för elbilsbatterier, främst från kraschade eller defekta bilar, växer och beräknas räcka för att konvertera majoriteten av gamla bensinbilar som är i gott skick. Livslängden för begagnade batterier vid konvertering uppskattas vara lika med resten av chassit, på grund av de lägre effektkraven i konverteringsbyggen. Vi ser att denna lösning har potential i det större perspektivet, främst igenom utbudet och livslängd av batterier och chassin för konverteringar. Men också att kostnaden och kompexiteten är tillräkligt låg om de vanligaste modellerna används. Denna lösning är just nu bara tillgänglig i sverige och ett fåtal andra länder där det är lagigt att modifiera sina bilar.

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