Lithium-ion batteries are of great importance for today's society. The state-of-the-art batteries that are used today use a fluorinated electrolyte that contains the salt LiPF6 and acts as both a safety hazard and an environmental issue due to its ability to form the toxic gas hydrogen fluoride (HF). This project aims to find a fluorine-free electrolyte that can be used in silicon-based lithium-ion batteries to make them more environmentally friendly without detriment to the electrochemical performance. To do so, an additive that may form a solid electrolyte interphase (SEI) stable enough to allow a fluorine-free electrolyte to replace the ones used today is sought for. The salt of interest is lithium  bis(oxalato)borate (LiBOB). Based on previous research electrolytes using LiBOB in either the solvent γ-Butyrolactone (GBL) or a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are examined. The additives used are vinylene carbonate (VC) and 1,3,2-dioxathiolane 2,2-dioxide (DTD). Techniques used are cyclic voltammetry, linear sweep voltammetry, galvanostatic charge and discharge, X-ray photoelectron spectroscopy and scanning electron microscopy.  The cells using GBL as solvent have cycled very poorly during this project while LiBOB in EC:EMC + VC shows the most promising results, with highest capacity retention and less amount of degraded LiBOB during the first charge. It is also to be noted that both EC:EMC based electrolytes provide the formation of a passivating solid electrolyte interface (SEI) and are of interest for further investigation based on the results obtained during this project.

Stricter regulations concerning emissions from road traffic and increasing fuel prices has lead to an interest in hybrid electric vehicles (HEVs). Today even manufacturers of heavy duty vehicles are introducing hybrid alternatives. Batteries are expensive and a complex part in HEVs, and ways of determining a battery’s capacity is a current research topic. When a battery is used it ages, i.e. the capacity decreases and the impedance rises. Since battery cost is high, it is important to be able to determine battery ageing properly. The focus of this master thesis has been on impedance measurement methods for Li-ion batteries. The work has been carried out in cooperation with Scania CV AB. When a battery is aged, the impedance increases. Monitoring ageing mechanisms could enable increased lifetime of the batteries through optimized usage in for example heavy duty hybrid vehicles. In this work, Hybrid Pulse Power Characterization (HPPC) has been compared with Electrochemical Impedance Spectroscopy (EIS). A major difference between these methods is that HPPC uses pulses of high direct current, whereas a small alternating current perturbation is used in EIS. EIS give information about different mechanisms influencing the battery impedance, e.g. internal resistance and charge transfer resistance, but requires expensive and complex laboratory equipment. HPPC gives less detailed information about the impedance, but is more similar to field applications for a vehicle. A literature survey showed that much research is conducted on in-situ impedance measurements of batteries. One example is the long-term demonstration of an Impedance Measurement Box (IMB), which is currently carried out at Idaho National Laboratory. The method uses a sum-of-sines signal consisting of octave harmonics for a fast impedance measurement with good precision. The results showed a good correlation with laboratory EIS measurements. The experimental part of this project suggest that a linear correlation  exists between the discharge resistance from HPPC measurements and the sum of internal resistance and charge transfer resistance from EIS measurements. The linear fitting did not have very good R-squared value but a residual analysis showed that the residuals were randomly scattered around zero, indicating that a linear fitting is suitable. However, the precision of the results is too poor for the correlation to be useful in a real HEV application. Additional work to improve the linear fitting is recommended. Furthermore, it was showed that AC-components have to be used as a measurement signal in order to measure the complex impedance of a battery. A paired t-test was conducted in order to study if noise could be used as that signal for a battery under load. The impedance at 100 Hz was calculated, which corresponds to the second harmonic of the power grid. The difference between this impedance and the impedance measured at 100 Hz with EIS was statistically tested. For shorter times pans (in this case 20 milliseconds) after applying the DC pulse, using noise cannot be ruled out for measuring a battery’s impedance under load. But for longer time spans after applying the DC pulse (in this case 1.3 seconds), there was a significant difference between the two methods. Concentration gradients caused by mass transfer limitations could be causing this effect.

Lithium-ion batteries are a rapidly growing power source for mobile applications such as electric vehicles. A battery model algorithm that estimates and predicts important battery parameters like terminal voltage and state-of-charge is necessary to maintain safe operation during discharge. Hence, a semi-empirical electrochemical-based model was proposed and implemented in MATLAB for discharge simulation and parameter estimation. This thesis also investigated several essential factors like internal resistance and operational temperature, which impact a battery cell during discharge.  The proposed model was a modification of Shepherd’s model that included both kinetic and diffusive components representing the total battery overpotential and a temperature- dependent coefficient. These were used for the determination of the battery’s internal resistance and the temperature effect. The model accounts for all dynamic characteristics of a Li-ion battery, including non-linear open-circuit voltage, internal resistance, discharge current, and capacity.  Model validation was performed using test profiles, including data provided by the battery manufacturer and experimental data for a test profile provided by Saab Dynamics. The simulated profiles were found to match the measured profiles. Although, some deviations occurred, especially during rapid changes in C-rates. The proposed model in this work shows that the simulation results compared to the experimental data had deviations within ~2% for the constant current discharge test, and the dynamic model managed to cover the experimental discharge voltage during different temperatures with good consistency and minor errors. Therefore, the proposed model can compete with other battery modeling methods.

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)

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

No description available.

Silicon has emerged as a promising alternative to traditional graphite as an anode material in battery technology, primarily due to its high theoretical capacity and abundance. However, its application is hindered by significant challenges, including severe volume expansion in the active material (~275%) during cycling, which can lead to a series of electrode failure issues. Polymer binder plays an essential role in addressing these challenges as it accommodates silicon's volume expansion and the rearrangement of particles. This work conducted an analysis of how different binders influence mechanical and electrochemical properties of silicon electrodes. Our findings are supported by a series of experiments, aimed at addressing the challenge of silicon volume expansion and improving the durability and efficiency of silicon-based anodes. Water-soluble polyacrylic acid (PAA) has emerged as a promising binder material for silicon anodes, with lithium hydroxide (LiOH) frequently added to improve the rheological properties of the slurry. However, literature presents varying results regarding the electrochemical performance of batteries incorporating LiOH in PAA binders. In addressing these discrepancies, our research investigates the role of LiOH in PAA, defining its impact through two primary factors: lithium-ion concentration and pH level. Our analysis involved conducting cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests, which confirmed our hypothesis that the addition of Li+ ions improves ion transport. Regarding pH, an optimal middle-ground pH level is identified, balancing the advantages shown at both lower and higher pH ranges. Despite the observed benefits of water-soluble PAA binder, such binders frequently result in uneven carbon distribution in coating, attributed to the poor wettability of nano-carbon in water. Consequently, the next portion of this work revisits the use of a traditional NMP (N-Methyl-2-pyrrolidone) soluble binder, PVDF (polyvinylidene fluoride), known for its widespread application in battery technology. However, PVDF-based silicon anodes often exhibit poor cycling performance. To address this issue and enhance the binder's flexibility, we attempted to chemically modify PVDF by incorporating carboxylic acid (-COOH) groups and reducing the polymer chain length. Despite these efforts, the experimental results did not show an improvement in cycling performance. The findings suggest that the deteriorated performance may be due to a weakened adhesion to the current collector for short-chain polymers. We then explore additional binder systems in an attempt to improve Si electrode performance. Our previous research suggests a trade-off between flexibility and adhesion in shortened polymers. To further verify this, we investigate the effect of two commercially available short-chain polymer binders, namely Jeffamine D-2000 and PAA(2000). Next, in order to mitigate the adverse effects of short polymer chain lengths on mechanical performance, we adopt an adhesion layer between the bulk electrode layer and the current collector. Finally, we evaluate several binders known for their promising results in other battery systems, including polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and polyimide (PI). A series of mechanical and electrochemical characteristics of the as-mentioned binders are investigated. The findings confirm that shorter polymer chain length leads to a weaker adhesion between the electrode coating and the current collector. Additionally, we discovered that introducing an adhesion layer can enhance the cycling stability of silicon anodes.

Ce travail de thèse porte sur la réalisation d’une batterie redox-flow fonctionnant grâce à la circulation de suspensions de matériaux d’insertion du lithium afin d’accroitre leur densité d’énergie. Le recours à des cellules microfluidiques permet de s’affranchir des limitations causées par les membranes échangeuses d’ions. Il s’articule dans un premier temps sur la synthèse contrôlée par voie hydrothermale de nanoparticules de LiCoO2 et leur caractérisation en suspension aqueuses. Cette étape permet de déterminer à la fois les propriétés électrochimiques des suspensions, leur état d’agrégation ainsi que leur comportement rhéologique en vue d’une utilisation redox-flow. Le transfert électronique entre une particule en suspension et les électrodes de la cellule est un aspect fondamental de ce type de batteries. Ce transfert est étudié grâce la technique de collision électrochimique dans laquelle la réponse de chaque agrégat est détecté individuellement par une ultramicroélectrode ce qui permet d’établir de nombreuses propriétés physique-chimiques de ces suspensions. Ce travail propose ensuite de s’affranchir de l’utilisation des membranes et de leurs limitations par le recours aux techniques de la microfluidique. La formation d’un écoulement co-laminaire en microcanal permet d’obtenir une cellule redox-flow opérationnelle. La conception et le fonctionnement de ces cellules est étudié en vue de la mise en circulation de suspensions de nanoparticules dans ce type de systèmes. / The aim of this work is to make a redox-flow battery that runs on lithium insertion material suspensions in order to increase the energy density of such systems. The use of microfluidic technics allows to solve the issues and limitations of ion exchange membrane by removing them. In the first part controlled size LiCoO2 nanoparticles are synthesized by hydrothermal route and dispersed into suspensions. The aggregation state of these suspensions are investigated using diffusion light scattering and transmission electronic cryoscopy. Rheological properties were also characterized for redox-flow use. The electronic transfer between a particle in suspension and the flow cell electrodes is crucial for their performances. This transfer is studied in the second part using the single event collision technic which consist of isolating individual aggregate electrochemical response at the surface of an ultramicroelectrode. This approach allows an extensive investigation of suspensions aggregates size, mobility and insertion reaction kinetic. Finally this works propose to replace the conventional ion exchange membrane by the mean of microfluidic technics. In co-laminar condition the fluid interface acts as a separation membrane to create a membrane-less redox-flow battery. The last part focuses on the fabrication of microfluidic cells and the behavior of suspensions in micro-channels.