Graphite has important applications in several key industries, which has been listed as a “criticalraw material” considered to be supply-risk by European since 2020. Purification of engineered graphite is one of the essential processes for the manufacturing of high-quality graphite. In this work, the production process and the existing methods to purify the three major types of graphite are evaluated and compared. Then purification method focusing on acid washing to remove iron from bio-graphite is investigated. The results showed that the impurity removalefficiency of acid washing increases with the increase of temperature, but efficiency decreased because of HCl volatilization when the temperature reaches 100 ℃. High concentrations of hydrochloric acid and other strong acids can improve the ability of acid washing. The smaller the graphite particle size, the more iron impurities are removed. Finally, through multi-steps acid washing with hydrochloric acid and aqua regia at 80 °C, bio-graphite with a purity of 99.67 % was obtained. This meets the requirements of metallurgical electrodes and other applications. The acquisition of ultra-high-purity graphite still needs more further work. / Grafit har viktiga tillämpningar i flera nyckelindustrier, som har listats som en "kritisk råvara" som anses vara en försörjningsrisk av Europa sedan 2020. Rening av teknisk grafit är en av de väsentliga processerna för tillverkning av högkvalitativ grafit. I detta arbete utvärderas och jämförs produktionsprocessen och de befintliga metoderna för att rena de tre huvudtyperna av grafit. Därefter undersöks reningsmetod med fokus på syratvätt för att avlägsna järn från biografit. Resultaten visade att effektiviteten för avlägsnande av föroreningar vid syratvätt ökar med ökningen av temperaturen, men effektiviteten minskade på grund av HCl-förångning när temperaturen når 100 ℃. Höga koncentrationer av saltsyra och andra starka syror kan förbättra förmågan till syratvätt. Ju mindre grafitpartikelstorlek, desto mer järnföroreningar avlägsnas. Slutligen erhölls biografit med en renhet på 99,67 % genom syratvätt i flera steg med saltsyra och aqua regia vid 80 °C. Detta uppfyller kraven för metallurgiska elektroder och andra applikationer. Förvärvet av grafit med ultrahög renhet kräver fortfarande mer arbete.

Demand for high-quality graphite is expected to experience an extraordinary growth rate, in large part due to its wide range of industrial applications such as adsorbents, lubricants, electrodes, etc. This thesis developed a novel sustainable approach to produce green-graphite materials by applying biochar, acarbon-rich valuable by-product obtained from biomass, as a carbon precursor. Meanwhile, iron-based catalysts are applied to enable the graphitization at a relatively lower temperature. This study focuses on the different parameters which could affect the evolution of carbon structure. The samples were mixed with catalyst in two ways, dry mixing and wet impregnation. Aside from the addition method, several parameters including temperature, heating duration, and iron loading amount were varied from 800 to 1300 ℃, 1 to 6 hours, and 0 to 33.6% respectively, to figure out an optimum graphitization process. The samples were characterized by X-ray diffraction, Raman scattering, SEM and particle size distribution analysis. Based on the characterization results, it was confirmed that with the increase of the graphitization temperature, duration and amount of iron loading, synthetic graphite performs a better graphitization and a higher conversion rate. Meanwhile, a detailed dissolution-precipitation mechanism was introduced and discussed in the context of iron-carbon equilibrium phase diagram to explain this catalytic process. / Efterfrågan på högkvalitativ grafit förväntas uppleva en extraordinär tillväxttakt, till stor del på grund av dess breda utbud av industriella applikationer som adsorbenter, smörjmedel, elektroder etc.  Denna avhandling utvecklar ett nytt hållbart tillvägagångssätt för att producera grön-grafit genom att använda biokol, en kolrik värdefull biprodukt erhållen från biomassa, som en kolprekursor. Även järnbaserade katalysatorer används för att möjliggöra grafitisering vid relativt lägre temperaturer. Denna  studie fokuserar på  de olika  parametrar  som  kan  påverka  bildandet  av kolstrukturen. Proverna blandades med katalysatormaterialet på två sätt, torrblandning och våtimpregnering. Förutom tillsatsmetoden justeras flera andra parametrar, inklusive temperatur, uppvärmningstid och mängd järnbelastning för  att  få  en optimal  grafitiseringsprocess.  Proverna karakteriserades därefter genom röntgendiffraktion, Ramanspridning, SEM och  partikelstorleksfördelningsanalys. Baserat på karakteriseringsresultaten bekräftades det att med en ökande grafitiseringstemperatur, varaktighet och mängd av järnbelastning, får syntetisk grafit en bättre grafitisering och en högre omvandlingsgrad. Även en detaljerad upplösnings-utfällningsmekanism introducerades och diskuterades i sammanhanget av järn-kol jämviktsfasdiagrammet  för  att förklara den katalytiska processen.

Cylinder liners in heavy-duty truck engines are subjected to intense vibrations and may sustain damage from the cavitation of bubbles in the coolant liquid, with some risks of leakage and engine breakdown. An ultrasonic oscillating probe was used to simulate the pitting rates and behavior of samples extracted from cylinder liners, which are made of grey cast iron, with differences in surface roughness, glycol and inhibitor content in coolant, coolant temperature and graphite flake class; bainitic microstructures were also tested. Measurements consisted of mass losses under set intervals during experiments lasting 2.5 or 4 hours. Affected surfaces were later evaluated with scanning electron microscopy and confocal microscopy. Results indicate higher cavitation damage with: lower concentrations of glycol and absence of corrosion/cavitation inhibitors in the coolant liquid, lower liquid temperatures between 76⁰C and 90⁰C, and presence of B-type graphite class in the microstructure. Results regarding surface roughness were inconclusive. A sequence of surface damage mechanisms has been proposed, with corresponding microscope observations, to explain the mass loss trends and the associated microstructural changes over time.

The strength and success of the hydrogen economy relies heavily on the storage of hydrogen. Storage systems in which hydrogen is sequestered in a solid material have been shown to be advantageous over storage of hydrogen as a liquid or compressed gas. Many different types of materials have been investigated, yet the desired capacity and uptake/release characteristics required for implementation have not been reached. In this work, porphyrin aggregates were investigated as a new type of material for hydrogen storage. The building blocks of the aggregates are porphyrin molecules that are planar and can assume a face to face arrangement that is also known as H-aggregation. The H-aggregates were formed in solution, upon mixing of aqueous solutions of two different porphyrins, one carrying positively charged and the other one carrying negatively charged functional groups. The cationic porphyrin used was meso-tetra(4- N,N,N-trimethylanilinium) porphine (TAP) and it was combined with four different anionic porphyrins, meso-tetra(4-sulfonatophenyl)porphine (TPPS), meso-tetra(4-carboxyphenyl) porphine (TCPP), Cu(II) meso-tetra(4-carboxyphenyl) porphine, and Fe(III) meso-tetra(4- carboxyphenyl) porphine. The force of attraction that held two oppositely charged porphyrin molecules together was electrostatic attraction between the peripheral groups. Solid state aggregates were successfully isolated either by solvent evaporation or by centrifuging and freeze drying. TCPP-TAP and Cu(II)TCPP-TAP aggregates were shown to interact with hydrogen starting from 150 °C up to 250 °C. The uptake capacity was about 1 weight %. Although this value is very low, this is the first observation of porphyrin aggregates absorbing hydrogen. This opened the way for further research to improve hydrogen absorption properties of these iv materials, as well as other materials based on this model. Two other materials that are also based on planar building blocks were selected to serve as a comparison to the porphyrin aggregates. The first of those materials was metal intercalated graphite compounds. In such compounds, a metal atom is placed between the layers of graphene that make up the graphite. Lithium, calcium and lanthanum were selected in this study. Theoretical hydrogen capacity was calculated for each material based on the hydriding of the metal atoms only. The fraction of that theoretical hydrogen capacity actually displayed by each material increased from La to Ca to Li containing graphite. The weight % hydrogen observed for these materials varied between 0.60 and 2.0 %. The other material tested for comparison was KxMnO2, a layered structure of MnO2 that contained the K atoms in between oxygen layers. The hydrogen capacity of the KxMnO2 samples was similar to the other materials tested in the study, slightly above 1 weight %. This work has shown that porphyrin aggregates, carbon based and manganese dioxide based materials are excellent model materials for hydrogen storage. All three materials absorb hydrogen. Porphyrin aggregates have the potential to exhibit adjustable hydrogen uptake and release temperatures owing to their structure that could interact with an external electric or magnetic field. In the layered materials, it is possible to alter interlayer spacing and the particular intercalates to potentially produce a material with an exceptionally large hydrogen capacity. As a result, these materials can have significant impact on the use of hydrogen as an energy carrier.

Granular superconductivity at high temperatures in graphite can emerge at certain two-dimensional (2D) stacking faults (SFs) between regions with twisted (around the c-axis) or untwisted crystalline regions with Bernal (ABA…) and/or rhombohedral (ABCABCA…) stacking order. One way to observe experimentally such 2D superconductivity is to measure the frozen magnetic flux produced by a permanent current loop that remains after removing an external magnetic field applied normal to the SFs. Magnetic force microscopy was used to localize and characterize such a permanent current path found in one natural graphite sample out of ∼50 measured graphite samples of different origins. The position of the current path drifts with time and roughly follows a logarithmic time dependence similar to the one for flux creep in type II superconductors. We demonstrate that a ≃10 nm deep scratch on the sample surface at the position of the current path causes a change in its location. A further scratch was enough to irreversibly destroy the remanent state of the sample at room temperature. Our studies clarify some of the reasons for the difficulties of finding a trapped flux in a remanent state at room temperature in graphite samples with SFs.

<p>In the pursuit to develop safe and reliable lithium-ion batteries, it is imperative to understand all the variabilities that revolve around electrodes. Current cutting-edge physics-based simulations employ an image-based technique. This technique uses images of electrodes to extract effective properties that are used in these physics-based simulations or employ the simulation on the structure itself. Though the electrode images have spatial variability, various particle morphology, and aberrations that need to be accounted for. This work seeks out to help quantify these variabilities and pinpoint uncertainties that arise in image-based simulations by using machine learning and other data analytic techniques. First, we looked at eighteen graphite electrodes with various particle morphologies to gain a better understanding on how heterogeneity and anisotropy interplay with each other. Moreover, we wanted to see if higher anisotropic particles led to greater heterogeneity, and a higher propensity for changes in effective properties. Multiple image-based algorithms were used to extract tortuosity, conductivity, and elucidate particle shape without the need for segmentation of individual particles. What was found is highly anisotropic particles induces greater heterogeneity in the electrode images, but also tightly packed isotropic particles can do the same. These results arise from porous pathways becoming bottlenecked, resulting in greater likelihood to change values with minimal changes in particle arrangement. Next, a model was deployed to see how these anisotropies and heterogeneities impact electrochemical performance. The thought of whether particle morphology and directional dependencies would have impact on plating energy and heat generation, leading to poor electrochemical performance. By using a pseudo-2D model, we elucidated that the larger the tortuosity the greater the propensity to plate and generate heat. Throughout these studies, it became clear that the segmentation of the greyscale images became the origin for subjectiveness to appear in these studies. We sought to quantify this through machine learning techniques, which employed a Bayesian convolutional neural network. By doing so we aimed to see if image quality impacts uncertainties in our effective properties, and whether we might be able to predict this from image characteristics. Being able to predict effective property uncertainty through image quality did not prove possible, but the ability to predict physics properties based on geometric was able to be done. With the largest uncertain particles occurring at the phase boundaries, morphologies that have a large specific surface area presented with the highest structural uncertainty. Lastly, we wanted to see the impact carbon binder domain morphology uncertainty impacts our effective properties. By using a set of sixteen NMC electrodes, which specify the carbon binder domain weight percentage, we can see how uncertainties in morphology, segmentation, spatial variability, and manufacturing variability impact effective properties. We expected there to be an interplay on which uncertainty impacts various effective properties, and if manufacturing variability plays a large role in determining this. By using surrogate models and statistical methods, we show that there is an eb and flow in uncertainties and effective properties are dependent on which uncertainty is being changed.</p>

The thermal management of electric machines is investigated with the application of techniques to a Switched Reluctance Machine and a high-speed Switched Reluctance Machine. Two novel concepts for said management of a Switched Reluctance Machine are proposed and developed: Inter-Laminate Cooling and a Continuous Toroidal Winding. The Inter-Laminate Cooling concept is developed with application to an iron core inductor which serves as a proxy for the electric machine. The experimental results confirmed the capability of the method, expressed by the effectiveness, which defines the performance measure of the applied cooling method; a concept which itself is equally applicable to other cooling methods that may be applied to any electric machine. The effectiveness also describes the gain in allowable input power to the machine which is realized to reach the same thermal limit versus the case without Inter-Laminate Cooling. The Inter-Laminate Cooling was not applied in experimental test to a Switched Reluctance Machine due to the present economic and fabrication limitations. The Continuous Toroidal Winding concept, originally conceived to permit the consideration of a fluid capillary core type of winding to enhance machine cooling, is developed to allow for peripheral cooling of the machine windings and end windings. The Continuous Toroidal Winding version of the Switched Reluctance Machine is investigated for both its thermal and electrical performance in the context of a machine that is equivalent electromagnetically to its conventional counterpart. The Continuous Toroidal Winding Switched Reluctance Machine was found to perform thermally as tested, in a manner superior to that of the conventional machine where the Toroidal machine was simulated and researched at an equivalent level of operation to the conventional machine. The electrical performance of the Toroidal Switched Reluctance Machine although supportive of the simulation analysis used to develop the machine, was not fully conclusive. This may have been due to problematic iron cores used in the construction of the experimental machines. The application of the Inter-Laminate Cooling method to a Switched Reluctance Machine is considered on an analytical basis for the special case of a High Speed Switched Reluctance Machine and found to be of net positive benefit as the machine’s iron losses are dominant over its copper losses. Application of the Inter-Laminate Cooling method to a lower speed machine, whilst beneficial, is not sufficient to significantly impact the temperature of the machine’s windings such that it would offset the loss of specific torque and power. As such, Inter-Laminate Cooling is only applicable where the net benefit is positive overall; in that the gain in input power realized is sufficient to overcome the loss of specific power and torque which will occur due to the increased machine volume. The “effectiveness” and “gain” approach for the evaluation of cooling methods applied to electric machines is a concept which should be adopted to aid in the comparative understanding of the performance of myriad different cooling methods being applied to electric machines both in research and practice, of which there is only minimal understanding. / Thesis / Doctor of Philosophy (PhD)

Li-ion batteries have enabled the widespread adoption of portable electronics and are becoming the technology of choice for electric vehicles and grid storage. One of the most promising ways to accommodate this demand is to increase the energy density and cycle life of battery electrode materials. Key strategies promoted in the literature include the use of nickel-rich cathodes as well as high-capacity anodes like silicon and lithium metal. While these materials enable a high energy density, this advantage is often counterbalanced with deficits such as poor stability and high cost. Multicomponent electrodes refer to strategies that try to leverage the relative advantages of different materials to offer an attractive compromise of energy density, cost, and cycle life. This thesis has investigated various aspects of multicomponent electrodes with a special emphasis on silicon-based anodes and high-entropy materials. Silicon (Si) is the second-most abundant element on earth and has one of the highest gravimetric capacities. However, silicon anodes are notorious for their poor cycle stability. Herein, improvements in the stability of silicon-based electrodes are achieved with multicomponent composite strategies involving the use of nanostructured spherical silicon. The nanosilicon is studied in high-fraction (80 wt% Si) and low-fraction (≤20 wt% Si) formulations to investigate both failure mechanisms and practical capacity retention, respectively. Composite strategies in which nanosilicon is encapsulated within a Li₄Ti₅O₁₂ ceramic or MOF-derived carbon matrix are shown to deliver superior capacity retention compared to simple composites of silicon and graphite. Considerable attention is given to the selection of a water-soluble binder and its role in electrochemical stability and electrode cohesion in high-loading silicon electrodes. It is found that unmodified high-molecular-weight sodium carboxymethyl cellulose offers better capacity retention compared to xanthan gum or low-molecular-weight binders. The high-entropy design strategy has created a diverse and largely unexplored set of multicomponent oxides and alloys with great potential as electrode materials. This strategy is applied to the family of layered cathodes, where the synthesis and electrochemical properties of the best-performing Li(NiCoMnTiFe)₁O₂ are reported. Despite the low Ni content, the cathode delivers a high initial capacity with unique overlithiation stability despite being charged to 4.4 V. Throughout the thesis, Operando XRD is used to reveal important insight into the lithiation mechanisms of the multicomponent electrodes including intercalation-based graphite, alloying-based silicon, and a novel organic azaacene.

In today’s fast adjustment to renewable energy, new battery technologies are needed to meetthe ever-growing demands of energy storage. Cheaper and easier to produce materials areneeded, as well as materials with a lower environmental impact. One new and interestingtechnology is the dual-ion battery, and more specifically the aluminum dual-ion battery. Thisbattery uses cheap and abundant aluminum together with a graphitic cathode to work. However,a lot of research today uses expensive and sophisticated cathode materials to make this type ofbattery work. Therefore, this thesis focuses on creating a cheap and easy to produce graphitecathode material through the phase inversion method for the use in aluminum dual-ionbatteries, that is also freestanding for better energy density. Graphene is also used as anadditive to improve the electrical conductivity of the material, and the material is later tested in afull cell with the typical ionc liquid electrolyte EMImCL/AlCl4.Through phase inversion, a freestanding graphite cathode is produced with 8 wt% PVDF binderand 0.4 wt% graphene. The material has a porous structure and an enhanced electricalconductivity with the graphene added. Through CV cycling and symmetric Al-Al tests the batteryreactions are shown to work. However, when cycling the cell with a constant current there areproblems, probably coming from some sort of soft shorting or side reactions. It is revealed thatapart from the expected reactions, Ni dissolution from the contact tabs also takes place, andmay cause problems. Further tests are needed to validate if this material works. However,because no new active materials have been introduced to the battery chemistry, it is reasonableto believe that the battery will work with some small changes.Tek nisk-naturvetensk apliga fak ulteten, Upps ala universitet. Utgiv nings ort U pps al a/Vis by . H andledare: Anwar Ahniy az , Äm nesgranskar e: D aniel Brandell, Ex aminator: Lena Klintberg

Introduction. Defect-induced superconductivity is an important phenomenon manifested in triggering the superconducting state due to defects and disorder in the material lattice. Promising materials for this investigation are carbon-based. Josephson behavior has been reported in 1974 for a disordered graphite powder, which is considered to be the first hint of a room temperature graphite-based superconductor. Theoretical and experimental studies support the idea that certain two-dimensional stacking faults (SFs) in the semiconducting matrix contribute to the granular superconducting-like behavior of graphene-based materials. Hints for the existence of high-temperature superconductivity at certain SFs in graphite were demonstrated. This phenomenon is considered to be caused by flat band regions at the SF. Especially the SFs between Bernal and rhombohedral stacking orders (without any twist angle around the common c-axis) have the largest probability to show robust superconductivity due to an extended and robust flat band behavior. In this work, a permanent current path in graphite, after the application of a magnetic field, is investigated to show clear evidence for the existence of room temperature superconductivity (RTS). Preliminary results for the existence of such permanent current path were obtained with magnetic force microscopy (MFM) and published a few years ago. Thus, the objectives of this work are to investigate trapped magnetic flux with magnetic force microscopy, to reveal the reasons for the difficulties of finding such permanent current path in the remanent state of the sample and to give an additional hints to the semiconducting behavior and energy gaps of an ideal graphite using a new PF-TUNA method. Summary. The experimental pre-characterization of graphite samples was conducted using XRD and Raman spectroscopy. The spectra show well-ordered structure of the samples with a sufficient content of the rhombohedral phase. The grounded samples were examined with PF-TUNA mode at bias voltages applied between the conductive tip and the sample surface. The samples with Bernal phase and with mixed phases showed semiconductor-like behavior. Using the semiconductor model, the obtained simulations of registered I-V curves could estimate the energy gap in a range from 12 to 37 meV. This is in a good agreement with the values of energy gaps, observed in transport measurements. Additionally, the shift in the position of the minimum of the tunneling conductance was explained by the tip-induced band bending. The results of this thesis confirm the existence of the peak in the density of states, that is correlated to the flat band in a sufficiently thick multigraphene flake with a 3R stacking order (thickness should be much greater than 3 nm to observe it) at room temperature and the existence of the trapped magnetic flux, expulsed by the weakly coupled superconducting patches in the natural graphite sample. The trapped flux was identified and examined by MFM measurements at the surface of natural graphite sample in the remanent state. Therefore, we successfully reproduced the results reported in and performed field and time dependent measurements, that prove the superconducting origin of this phenomena. The modeling of the MFM signal was done according to the monopole tip approximation. The value of the permanent current was estimated in the range of 0.2 μA to 6 μA, which is consistent with literature. An accidental scratch on the sample surface allowed us to estimate the depth of the aforementioned superconducting patches, ≲ 10 nm, and gave additional evidence to its origin by changing the route due to the superconducting patches nearby. This investigation provides hints for room temperature superconductivity at certain SFs in graphite and clarifies the reasons for the difficulties of the trapped flux identification in graphite. Further research should be focus on the identification of the permanent currents by MFM at lower temperatures. Moreover, it would be helpful to understand, how to artificially produce extended SFs. Finally, it should be noted, that additional measurements should be performed in order to clarify the field dependence of trapped magnetic flux in graphite and the role of Pearl vortices. Collaboration and External Contributions. This work was conducted under the supervision of Prof. Dr. Pablo Esquinazi, Felix-Bloch-Institute for solid state physics, Division of Superconductivity and Magnetism, University of Leipzig. STEM images were made by Dr. W. Bölmann, University of Leipzig. X-ray diffraction was made by Mr. O. Baehre and Mr. T. Muenster at Institute of Mineralogy, Crystallography and Materials Science at the University of Leipzig. The Raman spectra were recorded by Mr. Tom Venus and Dr. Irina Estrela-Lopis, Institute of Medical Physics and Biophysics, University of Leipzig. The natural graphite samples from Brazil were provided by Prof. Dr. Ana Melva Champi Farfan from Universidade Federal do ABC in Santo Andre, Sao Paulo, Brazil. The natural graphite from Sri-Lanka by Mr. Henning Beth from Golden Bowerbird Pty Ltd. in Mullumbimby, Australia. The magnetoresistance measurement of a natural graphite sample from Sri-Lanka was performed by Dr. Christian E. Precker, AIMEN Technology Centre, Smart Systems and Smart Manufacturing, Artificial Intelligence and Data Analytics Laboratory, PI. Cataboi, Pontevedra, Spain. The calculations, related to modeling of the tunneling current based on the tip-induced band bending, were performed by Dr. Michael Schnedler, Peter Gruenberg Institut, Forschungszentrum Juelich.