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.

AParmi les différentes sources d’énergie, les microaccumulateurs tout solide au lithium sont de bons candidats pour l’alimentation de systèmes miniaturisés. Afin d’outrepasser les limitations actuelles de ces microsources, les films minces de germanium sont prometteurs comme matériau d’électrode négative de par leurs meilleures stabilités chimique et thermique, comparées à celles du lithium métal. Ce travail de thèse a consisté à développer et à optimiser le procédé de synthèse par pulvérisation cathodique magnétron d’électrodes de germanium en couches minces, dont les propriétés physiques ont été mises en relation avec les performances électrochimiques. L’analyse du comportement électrochimique en régime et sur la tenue en cyclage a mis en évidence l’influence de la morphologie et du dopage des films de germanium. Malgré d’importantes variations volumiques de l’électrode, une étude a permis de montrer la faisabilité d’une intégration de ces couches minces dans des microaccumulateurs tout solide Ge pré-lithié/ LiPON/ Li par des procédés basse température (compatibles Above IC). Avec ce type d’empilement, une capacité spécifique élevée de 50 µAh/cm² (» 800 µAh/cm².µm) a été maintenue sur une quarantaine de cycles sous 10 µA/cm². Diverses propositions ont été envisagées afin d’accroître la cyclabilité de ces dispositifs et de permettre la réalisation de microaccumulateurs Li-ion pour des applications en microélectronique. / Among the different energy sources, all solid state lithium microbatteries are the most promising candidates for the alimentation of miniaturised systems. In the aim of overcoming the current limitations of these micro power sources, germanium thin films prove to be a promising material as a negative electrode, due to their better chemical and thermal stability in comparison with metallic lithium. This PhD work was devoted to the development of germanium electrode coatings and the optimisation of their synthesis by magnetron sputtering. Their physical properties have been correlated to their electrochemical performances. The influence of the morphology and doping of the films on their electrochemical behaviour at different current densities and on the cyclability was established. Despite huge volumic variations of the electrode, this study showed the feasibility of integrating these films in Ge lithiated/ LiPON /Li microbatteries deposited by low temperature processes (Above IC compatibility). With this stack configuration, a stable specific capacity of 50 µAh/cm² (» 800 µAh/cm².µm) has been maintained during forty cycles. Different solutions have been suggested to improve the cyclability of all solid state microbatteries and the techniques used for directly depositing them on the electronic microcomponents.

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The aim of this thesis is to develop a better understanding about the degradation mechanisms occurring within lithium-ion cells which eventually lead to their failure. An introduction to the components and operation of Li-ion cells is followed by proposed degradation mechanisms which limit the lifetime of cells. These mechanisms and how they can be identified from electrochemical testing are discussed. Electrolyte additives can be used to improve the safety of Li-ion cells or decrease the rate of cell degradation. Different types of additives and testing methods are discussed followed by an introduction to high precision coulometry which can be used to detect the impact of additives on cycling performance. The High Precision Charger that was constructed for this project is described and shown to meet the desired precision. The use of additives and different materials to extend lifetime of cells is shown to be detectable through the use of high precision coulometry. High precision coulometry proves to be a more efficient way of estimating the lifetime of cells under realistic conditions in a reasonably short amount of time. / MSc. Thesis

Four topics are presented in this thesis. Firstly, a new design for a combinatorial electrochemical cell plate based on circuit board technology is described. The new combinatorial cell plate was tested using sputtered silicon and capacity as a function of mass was determined. The measured specific capacity was 3580 mAh/g, which corresponds to Li15Si4 stoichiometry. The irreversible capacity was measured to be less than 2% of the reversible capacity. This design reduced the spurious capacity that came from the lead pattern of the old plate. Second, the role of oxygen content on the electrochemical properties of sputtered Si1-xOx was investigated. All the prepared thin film samples had an amorphous or nanostructured nature. The measured specific capacity (first charge) suggests that Si1-xOx is made up of amorphous silicon that reacts reversibly with lithium, and SiO2 that forms inactive Li4SiO4 after the first lithiation. The current study shows that the irreversible capacity is directly proportional to the oxygen content. This study indicates clearly that in order to produce material with high capacity, oxygen should be minimized to reduce Li consumption during Li4SiO4 formation. However, the Si:O ratio should be optimized to get a reasonable active: inactive ratio. Third, a systematic study to investigate the effect of the addition of carbon on the electrochemical performance of the Sn-Si binary is reported. This study involved the preparation and investigation of three pseudobinary libraries. The addition of carbon was found to inhibit the aggregation of tin and reduce the two-phase coexistence regions as evidenced by smooth differential capacity plots. This was reflected in the improved electrochemical performance such as reversible capacity and cycleability. Fourth, an investigation of carbon-rich alloys of Fe1-xCx is reported. Both x-ray diffraction and 57Fe Mössbauer spectroscopy were employed to get insight into the structural properties of this system. X-ray diffraction revealed the amorphous or nanostructured nature of all samples with different Fe:C ratios. The distribution of hyperfine parameters extracted from the Mössbauer analysis shows the existence of two components suggesting that Fe exists in two distinct sites: (1) Fe surrounded with Fe neighbors and (2) Fe surrounded with C neighbors. The asymmetric environment was found more pronounced as carbon content increases in the films. This was reflected by high quadrupole splitting in excess of 1.0 mm/s.

Nickel-manganese-cobalt oxide (NMC) cathode materials have been applied in most Li-ion batteries, but there are nevertheless some concerns regarding the stability of this material. High voltage and high temperature during charging have been shown to accelerate the dissolution of NMC due to the release of more acidic components because of rapid electrolyte decomposition. Mn-contaminants (Mn2+) are hypothesized to diminish the diffusion coefficient of Li+ in the electrolyte attributed to the competitive interaction between Mn2+ ions and Li+ ions. With characterizations including 7Li and 1H pulsed field-gradient nuclear magnetic resonance (PFG-NMR) spectroscopy, we demonstrated the Mn (II)-contaminants effect on diffusion coefficient on Li+ dynamics. Under the influence of deliberate manganese salt-additive to the electrolyte, the coin cell shows a capacity fading and unstable charging behavior. The PFG-NMR measurements also validated our hypotheses, as the results showing that Mn-containment causes decrease ~15% in the diffusion coefficient on Li-self diffusion. The activation energy for lithium-ion transport over the temperature range of (273 K - 303 K), was not changed by the presence of the Mn-contaminant electrolyte, which indicates the Mn (II) does not affect the Li-ion transport mechanism. The relative test also includes comparisons with other contamination, such as iron contamination from stain-less steels spacers and copper contamination from the current collector. Additionally, the lithium self-diffusion coefficient was tested before and after charging using a full battery configuration. In electrolytes containing manganese contaminants, a more significant decrease in the diffusion coefficient was observed after charging. Ideally, operando experiments can be used to observe the impact of manganese ions on the SEI. By combining both types of experiments, a closer approximation to the actual application conditions of market-used batteries can be achieved. / Thesis / Master of Science (MSc) / The increasing maturity of lithium battery technology has also promoted the advancement of the electric vehicle manufacturing industry. As an excellent new energy material, the application and development of lithium batteries will be the main trend in the future. However, while improving battery capacity and energy density, lithium batteries also face many challenges. The entire thesis work discusses how electrolyte degradation at high temperatures and high voltages accelerates the dissolution of transition metal manganese ions in NMC materials. The dissolution of manganese ions into the electrolyte creates a competitive effect with lithium ions, thereby reducing the performance of lithium batteries. Here, NMR technology was used to measure the negative effect of manganese ions on the self-diffusion coefficient of lithium ions in the electrolyte. Additionally, a set of operando experiments conducted at different discharge rates demonstrated the changes in mossy lithium and the solid electrolyte interface during the charge and discharge phases caused by pulse discharge. This also proved that such experimental designs can track the impact of manganese ions on the solid electrolyte interface and test the dissolution behavior and impact of manganese ions under different charge and discharge rates.

Li-ion batteries are currently the most efficient technology available for electrochemical energy storage. The technology has revolutionized the portable electronics market and is becoming a corner stone for large scale applications, such as electric vehicles. It is therefore important to develop materials in which the energy storage relies on abundant redox active species, such as iron. In this thesis, new iron based electrode materials for positive electrodes in Li-ion batteries were investigated. Lithium iron pyrophosphate (Li2FeP2O7) and two polymorphs of lithium iron sulphate fluoride (LiFeSO4F) were studied. For Li2FeP2O7, preferred oxidation of iron with different coordination numbers within the crystal structure was studied, and six-coordinated iron was found to be oxidized preferentially at lower potentials compared to five‑coordinated iron. Electrochemical cycling resulted in structural changes of Li2FeP2O7 through an increased Li-Fe mixing in the compound, forming a metastable state during battery operation. For tavorite LiFeSO4F, the influence of the amount of a conductive polymer (poly(3,4-ethylenedioxythiophene), or PEDOT) was studied. All the different amounts of PEDOT coating reduced the polarization significantly, but the trade-off between functionality and weight added also has to be considered. Additionally, the effect of densifying the electrodes to different degrees is reported, and was found to have a significant influence on the battery performance. Also triplite LiFeSO4F was coated with PEODT, and it was found that the electrochemical performance improved, but not to the same extent as for tavorite LiFeSO4F. The faster solid state transport of Li-ions in tavorite type LiFeSO4F possibly accounts for the difference in electrochemical performance. Together, the results presented herein should be of importance for developing new iron based materials for Li-ion batteries. / Av de idag tillgängliga teknologierna för elektrokemisk energilagring så har litium-jonbatterier de bästa egenskaperna när det gäller energiförluster och energilagringskapacitet. De har revolutionerat marknaden för portabel elektronik (telefoner, laptops etc.), och blir mer och mer viktiga för storskaliga tillämpningar såsom elbilar. För den typen av applikationer måste teknologin baseras på vanligt förekommande material och grundämnen, t.ex. järn. I den här avhandlingen har järnbaserade material för den positiva elektroden hos litium-jonbatterier studerats. Olika aspekter som påverkar spänningen och effektiviteten hos elektroderna har undersökts. Ett exempel på det är hur olika omgivningar kring järnatomerna i en förening påverkar spänningen hos ett batteri. För föreningen litiumjärnpyrofosfat visade det sig att sex närmaste grannar ger lägre spänning än fem närmaste grannar till järn. Dessutom har förändringar i föreningens struktur studerats då den används i ett batteri. Den här typen av grundforskning är viktig för förståelsen av nya elektrodmaterial i Li-jonbatterier. Ur en mer praktisk synvinkel så har elektroder baserade på en annan järnförening, litiumjärnsulfatfluorid, utvecklats. Ledningsförmågan hos dessa elektroder har förbättrats genom att belägga föreningen med ett ledande skikt, samt att mekaniskt pressa samman elektroderna genom mangling. Båda metoderna är viktiga för att tillverka välfungerande elektroder. Föreningen litiumjärnsulfatfluorid förekommer i två olika former, och en jämförelse av hur elektriskt ledande beläggningar påverkar de bägge materialen har också gjorts i den här avhandlingen. Tillsammans visar resultaten från de olika studierna på hur man kan arbeta och tänka kring utvecklingen av nya material för litium-jonbatterier.

The thesis is composed of two topics : a charger circuit of Li-ion batteries for wireless biomedical systems and a capacitor-less low dropout regulator¡]LDO¡^. The first topic discloses a charger circuit of Li-ion batteries using 2P4M 0.35-£gm CMOS process, which comprises a small bias circuit, a comparator with hysteresis, a transistor voltage divider circuit, a power MOS, and a Li-ion charger with a cut-off voltage and a recharge voltage. The proposed design receives a 13.56 MHz carrier with 5¡Ó0.2 V amplitude to charge the Li-ion batteries with a small constant current. The second topic reveals a low dropout regulator ¡]LDO¡^ without capacitor load and ESR, including a bias circuit, an error amplifier, and a Flipped Voltage Follower circuit generating a stable output voltage independent on different loads. The proposed design improves the input voltage limitation of Flipped Voltage Follower by compensating phase margin such that the proposed design shows a good transient response and stability without any output capacitor. The proposed LDO is implemented by 1P6M 0.18-um CMOS process, which can operate correctly given an input voltage range from 3.3~4.2 V.

Undesired reactions in Li-ion batteries, which lead to capacity loss, can consume or produce charge at either the positive or negative electrode. For example, the formation and repair of the solid electrolyte interphase consumes Li+ and e- at the negative electrode. Electrolyte oxidation at the positive electrode allows extra electrons (with corresponding electrolyte decomposition products) to be extracted at the electrode compared to the number which could be extracted in the absence of electrolyte oxidation. High purity electrolytes, various electrolyte additives, electrode coatings and special electrode materials are known to improve cycle life and therefore must impact coulombic efficiency. Careful measurements of coulombic efficiency are needed to quantify the impact of different battery materials on cell life time in only a few charge-discharge cycles and in a relatively short time. In order to make an impact on Li-ion cells for automotive and energy storage applications, where thousands of charge-discharge cycles are required, coulombic efficiency must be measured to an accuracy and precision of at least 0.01%. An instrument designed to make high-precision coulombic efficiency measurements on Li ion batteries is described in this thesis. Such measurements can be used to detect the influence of different electrode materials, voltage ranges, cell temperature, etc. on the performance of a cell. The effects of cycle induced and time-related capacity loss can be probed using experiments carried out at different C-rates. Precision differential voltage and capacity measurements can also be used to identify the different failure mechanisms that occur in full cells.

This thesis studies the self-discharge performance of recently developed rechargeable hybrid aqueous batteries, using LiMn2O4 as a cathode and Zinc as an anode. It is shown through a variety of electrochemical and ex-situ analytical techniques that many parts of the composite cathode play important roles on the self-discharge of the battery. It was determined that the current collector must be passive towards corrosion, and polyethylene was identified as the best option for this application. The effect of amount and type of conductive agent was also investigated, with low surface area carbonaceous material giving best performances. It was also shown that the state of charge has strong effects on the extension of self-discharge. More importantly, this study shows that the self-discharge mechanism in the ReHAB system involves the cathode active material and contains a reversible and an irreversible part. The reversible portion is predominant and is due to lithium re-intercalation into the LiMn2O4 spinel framework, and results from Zn dissolution into the electrolyte, which drives the Li+ ions out of the solution. The irreversible portion of the self-discharge occurs as a result of the decomposition of the LiMn2O4 material in the presence of the acidic electrolyte, and is much less extensive than the reversible process.