Different kinds of batteries suit different applications, and consequently several different chemistries exist. In order to better understand the limitations of low temperature performance, a Li-ion battery chemistry normally intended for room temperature use, graphite-Lithium Iron Phosphate, with 1 M LiPF6 ethylene carbonate:diethylene carbonate electrolyte, is here put under testing at -10°C and compared with room temperature cycling performance. Understanding the temperature limitations of this battery chemistry will give better understanding of the desired properties of a substitute using alternative materials. The experimental studies have comprised a combination of battery cycle testing, and surface analysis of the electrodes by Scanning Electron Microscopy and X-Ray Photoelectron Spectroscopy. Results showed that with low enough rate, temperature is less of a problem, but with increased charge rate, there are increasingly severe effects on performance at low temperatures. XPS measurements of low charge rate samples showed similar Solid Electrolyte Interface layers formed on the graphite anode for room- and low temperature batteries, but with indications of a thicker layer on the former. A section of the report handles specific low temperature battery chemistries. The conclusions- and outlook were made by comparing the results found in the study with earlier findings on low temperature Li-ion batteries and present possible approaches for modifying battery performance at lowered temperatures. / I detta projekt har litium-jon-batterier testats i avseende på sina lågtemperaturprestanda. Arbetet gjordes genom att testa och jämföra prestantda mellan prover vid -10°C och rumstemperaturprover. Med analytiska instrument studerades både den morfologiska och kemiska förändring som skett under användning. Vald batterikemi har varit av slaget grafit-litiumjärnfosfat med en typisk organisk elektrolyt. Denna batterikemi är inte på något sätt anpassad för lågtemperaturprestanda och med det hoppas kunna påvisas de effekter som en mer lämpligt lågtemperaturkemi åtgärdar, och förstå hur de gör det. Med låg temperatur uppkommer en större ’tröghet’ för de kemiska reaktioner som sker i ett batteri. Om designen inte är särskilt gjord för låg temperatur kan effekterna bli osäkra, rent av farliga. Risken ökar nämligen för plätering av metalliskt litium på den negativa elektroden, och skulle litiumdeponeringen växa i den riktning som kopplar samman batteriets poler så kortsluts systemet. Med den höga energidensitet som karaktäriserar litium-jon-batterier vore en kortslutning extra beklaglig då den organiska elektrolyten kan antändas, med en potentiell explosion som följd.Inom särskilda applikationer kan lågtemperaturmiljöer förväntas för ett batteri, till exempel för fordon. En elbil i skandinaviskt klimat skulle behöva fungera ohindrat även vintertid, då temperaturerna ofta når -10°C och lägre. Samtidigt får man påminnas om att litium-jon-batterierna är relativt moderna och ännu inte har fått något stort genomslag som framdrivningsmedel. Detta försätter bilindustrin i ett krafigt behov av omfattande forskning för att kunna ta strategiskt sunda beslut för att möjliggöra en ordentlig introducering av elbilar som trovärdig ersättare till de fossilt drivna bilarna. I linje med trenden att ständigt bygga säkrare bilar måste elbilarna kunna visa upp förutsägbarhet, och med detta pålitlighet och säkerhet. I detta arbetet erhölls resultat som visade på batterifunktion även vid den sänkta temperaturen, men med gränser för hur snabbt laddningöverföring kunde ske jämfört med i rumstemperatur. Bevis för bildande av skyddsfilm på anod efter 1.5 battericykler, snarlik komposition för -10°C - och rumstemperaturbatterier – men med vissa indikationer på ett tjockare bildat lager hos den senare. Därtill gjordes jämförelser med specifika lågtemperaturselektrolyter, där en skillnad i framförallt innehåll utav etylkarbonat (mindre andel vid lågtemperaturapplikationer) uppvisar stora förbättringar i kallare klimat. En sådan provblandning gjordes och uppvisade bättre prestanda vid -10°C än rumstemperaturbatterier med standardelektrolyt. Arbetet har utförts vid Institutionen för Kemi-Ångström vid Uppsala universitet.

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Lithium-ion batteries (LIBs) are receiving significant attention from both academia and industry as one of the most promising energy storage and conservation devices due to their high energy density and excellent safety. Graphite, the most widely used anode material, with limitations on energy density, can no longer satisfy the requirements proposed by new applications. Therefore, further improvement on the electrochemical performance of anodes has been long pursued, along with the development of new anode materials. Among potential candidates, Si and Sn based anodes are believed to be the most promising. However, the dramatic volume expansion upon Li-intercalation and contraction upon Li de-intercalation cause mechanical instability, and thus cracking of the electrodes. To overcome this issue, many strategies have been explored. Among them the most efficient strategies include introduction of a nanostructure, coupled with a buffering matrix and coating with a protective film. However, although cycling life has been significantly increased using these three strategies, the capacity retention still needs improvement, especially over extensive charge-discharge cycles. In addition, more efforts are still needed to develop new fabrication methods with low costs and high efficiency. To further improve mechanical stability of electrodes, understanding of the failure mechanisms, particularly, the failure mechanisms of Si and Sn nanomaterials is essential. Therefore, some of the key factors including materials fabrication and microstructural changes during cycling are studied in this work. Hollow Si nanospheres have proved to be have a superior electrochemical performance when applied as anode materials. However, most of fabrication methods either involve use of processing methods with low throughput, or expensive temporary templates, which severely prohibits large-scale use of hollow Si spheres. This work designed a new template-free chemical synthesis method with high throughput and simple procedures to fabricate Si hollow spheres with a nanoporous surface. The characterization results showed good crystallinity and a uniform hollow sphere structure. The substructure of pores on the surface provides pathways for electrolyte diffusion and can alleviate the damage by the volume expansion during lithiation. The success of this synthesis method provides valuable inspiration for developing industrial manufacturing method of hollow Si spheres.3D graphene is the most promising matrix that can provide the necessary mechanical support to Sn and Si nanoparticles during lithiation. 2D graphene, however, results in Sn/graphene nanocomposites with a continuous capacity fade during cycling. It is anticipated that this is due to microstructural changes of Sn, however, no studies have been performed to examine the morphology of such cycled anodes. Hence, a new Sn/2D graphene nanocomposite was fabricated via a simple chemical synthesis, in which Sn nanoparticles (20-200 nm) were attached onto the graphene surface. The content of Sn was 10 wt.% and 20 wt.%. These nanopowders were cycled against pure Li-metal and, as in previous studies, a significant capacity decrease occurred during the first several cycles. Transmission and scanning electron microscopy revealed that during long term cycling electrochemical coarsening took place, which resulted in an increased Sn particle size of over 200 nm, which could form clusters that were 1 m. Such clusters result in a poor electrochemical performance since it is difficult for complete lithiation of the Sn to occur. It is hence concluded that the inability of Sn/2D graphene anodes to retain high capacities is due to coarsening that occurs during cycling. In addition to using forms of carbon to buffer the Sn expansion, it has been proposed to alloy Sn with S, which has a low redox potential vs Li⁰/Li⁺. Therefore, another new anode proposed here is that of SnS attached to graphite. The as prepared powders had a flower-like structure of the SnS alloy. Electrochemical cycling and subsequent microstructural analysis showed that after electrochemical cycling this pattern was destroyed and replaced by Sn and SnS nanoparticles. Based on the electron microscopy and XRD analysis, it was concluded that selective leaching of S occurs during lithiation of SnS particles, which results into nano SnS and Sn particles to be distributed throughout the electrolyte or SEI layer, without being able to take part in the electrochemical reactions. This mechanism has not been noted before for SnS anodes and indicates that it may not be possible to retain the initial morphology of SnS alloy during cycling, or the ability of SnS to be active throughout long term cycling. To conclude it should be stated that the goal and novelty of this thesis was (i) the fabrication of new Si, Sn/graphene and SnS/C nanostructures that can be used as anodes in Li-ion batteries and (ii) the documentation of the mechanisms that disrupt the initial structural stability of Sn/2D graphene and SnS/C anodes and result in severe capacity loss during long term cycling (over 100 cycles). These systems are of high interest to the electrochemistry community and battery developers.

A key metric that affects Li-ion battery cell performance is the electronic conductivity of the electrode films. Previous research has found that the conductivity of electrodes is not homogeneous throughout the entirety of the deposited film area. To further characterize the non-homogeneity of the conductivity of electrode films, a micro-N-line probe and a micro-flex-line probe were developed to take micro-scale conductivity measurements of thin-film battery electrodes in a non-destructive manner. These devices have been validated by comparing test results to those of it's predecessor, the micro-four-line probe, on various commercial-quality Li-ion battery electrodes. Results show that there is significant variation in conductivity on a millimeter and even micrometer length scale throughout the electrode film. Compared to the micro-four-line probe, the micro-N-line probe and micro-flex-line probe perform six times as many measurement configurations made on contact with the electrode, while providing a more robust design. Design improvements on the micro-four-line probe in order to fabricate the micro-flex-line probe are the main focus of this thesis. Researchers and manufacturers can use this probe to identify heterogeneity in their electrodes during the fabrication process, which will lead to the development of better batteries.

Nowadays personal small electronic devices like cellphones are more and more popular, but the various batteries in need of charging become a problem. This thesis aims to explain a Lithium-ion charger which can control the current and voltage so that it can charge most kinds of popular batteries. More specifically, Li-ion battery charging is presented. The charging circuit design, simulation and the measurements will also be included.

The main goal of this research was to apply first-principles electronic structure calculations to investigate atomic motions in several condensed materials. This thesis consists of five separate but related topics that are classified into two main categories: structure of materials under pressure and Li ion dynamics in lithium battery materials. The atomic structure of liquid gallium was investigated in order to resolve a controversy about an anomalous structural feature observed in the x-ray and neutron scattering patterns. We explored the pressure effect when modifying the liquid structure close to the solid-liquid melting line. The atomic trajectories obtained from first-principles molecular dynamics (FPMD) calculations were examined. The results clarified the local structure of liquid gallium and explained the origin of a peculiar feature observed in the measured static structure factor. We also studied the structure of a recently discovered phase-IV of solid hydrogen over a broad pressure range near room temperature. The results revealed novel structural dynamics of hydrogen under extreme pressure. Unprecedented large amplitude fluxional atomic dynamics were observed. The results helped to elucidate the complex vibrational spectra of this highly-compressed solid. The atomic dynamics of Li ions in cathode, anode, and electrolyte materials - the three main components of a lithium ion battery - were also studied. On LiFePO4, a promising cathode material, we found that in addition to the commonly accepted one-dimensional diffusion along the Li channels in the crystal structure, a second but less obvious multi-step Li migration through the formation of Li-Fe antisites was identified. This discovery confirms the two-dimensional Li diffusion model reported in several Li conductivity measurements and illustrates the importance of the distribution of intrinsic defects in the enhancement of Li transport ability. The possibility of using type-II clathrate Si136 as an anode material was investigated. It was found that lithiated Si-clathrates are intrinsic metals and their crystal structures are very stable. Calculations revealed the charge and discharge voltages are very low and almost independent of the Li concentrations, an ideal property for an anode material. Significantly, migration pathways for Li ions diffusing through the cavities of the clathrate structures were found to be rather complex. Finally, the feasibility of a family of Li3PS4 crystalline and nanoporous cluster phases were studied for application as solid electrolytes. It was found that the ionic conductivity in the nanocluster is much higher than in crystalline phases. It is anticipated that the knowledge gained in the study of battery materials will assist in future design of new materials with improved battery charge and discharge performance.

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)