This thesis encompasses the successful synthesis, characterization (NMR, IR, TGA) and electrochemical testing of novel, potentially redox-active organic materials. These were destined as electrodes for Li-organic cells and/or as catalysts for Li–O2 cells. The electrochemical performance of the dilithiated and tetralithiated salts of 2,5-dialkylamide hydroquinones (with ethyl, isopropyl or benzyl as the alkyl group) and of a partially lithiated polymer with a backbone of alternating 2,5-dicarbonylhydroquinone and 1,4-benzyl diaminophenylene units was evaluated. The small organicsalts exhibited redox-activity around 1.0 V vs Li/Li+ (the terephthaloyl redox system) and 2.8 V vs Li/Li+ (the quinone redox system). These values drifted depending on lithiation degree and alkyl substituent. Redox irreversibility featured these materials which decomposed and dissolved. The polymer exhibited multiple redox-activity in the region of 2.5-3.6 V vs Li/Li+, which was however also irreversible. Further on, the small organic salts were tested as to their impact on the dischargeproduct (Li2O2) yield in Li-O2 cells. Discharge profiles of cells with and without the inclusion of the salts were contrasted to each other; the former having a jagged appearance, indicative of side-reactions. The O2 electrode was studied by XRD todetect the formed products and the amount of Li2O2 present was quantified throug htitration and UV-vis spectroscopy. Organic salt inclusion was found to negatively affect the Li2O2 formation and also attack the Li-electrode.

Thesis advisor: Dunwei Wang / The performance of advanced energy storage devices is intimately connected to the designs of electrodes. To enable significant developments in this research field, we need detailed information and knowledge about how the functions and performances of the electrodes depend on their chemical compositions, dimensions, morphologies, and surface properties. This thesis presents my successes in synthesizing and characterizing electrode materials for advanced electrochemical energy storage devices, with much attention given to understanding the operation and fading mechanism of battery electrodes, as well as methods to improve their performances and stabilities. This dissertation is presented within the framework of two energy storage technologies: lithium ion batteries and lithium oxygen batteries. The energy density of lithium ion batteries is determined by the density of electrode materials and their lithium storage capabilities. To improve the overall energy densities of lithium ion batteries, silicon has been proposed to replace lithium intercalation compounds in the battery anodes. However, with a ~400% volume expansion upon fully lithiation, silicon-based anodes face serious capacity degradation in battery operation. To overcome this challenge, heteronanostructure-based Si/TiSi2 were designed and synthesized as anode materials for lithium ion batteries with long cycling life. The performance and morphology relationship was also carefully studied through comparing one-dimensional and two-dimensional heteronanostructure-based silicon anodes. Lithium oxygen batteries, on the other hand, are devices based on lithium conversion chemistries and they offer higher energy densities compared to lithium ion batteries. However, existing carbon based electrodes in lithium oxygen batteries only allow for battery operation with limited capacity, poor stability and low round-trip efficiency. The degradation of electrolytes and carbon electrodes have been found to both contribute to the challenges. The understanding of the synergistic effect between electrolyte decomposition and electrode decomposition, nevertheless, is conspicuously lacking. To better understand the reaction chemistries in lithium oxygen batteries, I designed, synthesized, and studied heteronanostructure-based carbon-free inorganic electrodes, as well as carbon electrodes whose surfaces protected by metal oxide thin films. The new types of electrodes prove to be highly effective in minimizing parasitic reactions, reducing operation overpotentials and boosting battery lifetimes. The improved stability and well-defined electrode morphology also enabled detailed studies on the formation and decomposition of Li2O2. To summarize, this dissertation presented the synthesis and characterization of inorganic nanostructured materials for advanced energy storage. On a practical level, the new types of materials allow for the immediate advancement of the energy storage technology. On a fundamental level, it helped to better understand reaction chemistries and fading mechanisms of battery electrodes. / Thesis (PhD) — Boston College, 2015. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Hunting for improved energy storage devices based on rechargeable Li-ion batteries and other advanced rechargeable batteries is one of the hottest topics in today's society. Both Li- ion batteries and Li-O2 batteries have been studied within the thesis. The research work of this thesis contains two different parts. Part 1. The controlled synthesis of the extreme small sized nanoparticles and their application for Li-ion batteries; Part 2. The study of the O2 reduction mechanism in Li-O2 batteries with aprotic electrolytes. In the first part, two different types of extremely small-sized TiO2 nanoparticles with at lease on dimension less than 3 nm was synthesised via solvothermal/hydrothermal reaction, i.e., anatase nanosheets and TiO2(B). These nanoparticles were obtained without any contamination of long chain organic surfactants. A series of systematic characterisation methods were employed to analyse the size, phase purity, and surface condition. These extremely small-sized nanoparticles exhibit improved capacity, rate performance as anode materials for Li-ion batteries. The shapes of load curves of charge and discharge are significantly modified due to the reduced size of TiO2 nanoparticles. In chapter 3, we will see the variation of the capacity and the load curve shape of the anatase nanosheets according to their thickness and surface conditions. The origin of the excessive capacity is analysed based on the electrochemical data. It has been identified that both pseudocapacitive (interfacial) Li+ storage and the excessive Li+ -storage from the bulk contribute to the increased capacity. In chapter 4, the shape and size of the sub-3 nm TiO2(B) nanoparticles are studied, a method based the PXRD data is established. These nanoparticles demonstrate a reversible capacity of 221 mAh/g at a rate of 600 mA/g and remain 135 mAh/g at 18000 mA/g without significant capacity fading during cycling. In the last part, a systematic study of O2 reduction mechanism for aprotic Li-O2 batteries based on the combination of a series of electrochemical and spectroscopic data is presented. The novel mechanism unifies two previous models for the growth of Li2O2 during discharge, i.e., Li2O2 particle formation in the solution phase and Li2O2 film formation on the electrode surface. The new mechanism provides fundamental conceptions for the improvement of Li2O2 batteries and shed light on the future research of Li2O2 batteries.

High energy density batteries have garnered much attention in recent years due to their demand in electric vehicles. Lithium-oxygen (Li-O2) batteries are becoming some of the most promising energy storage and conversion technologies due to their ultra-high energy density. They are still in the infancy stage of development and there are many challenges needing to be overcome before their practical commercial application. Some of these challenges include low round-trip efficiency, lower than theoretical capacity, and poor rechargeability. Most of these issued stem from the poor catalytic performance of the cathode that leads to a high overpotential of the battery. In this doctoral work, Li-O2 cathodes containing nanoparticles of palladium were used to alleviate this problem. Cathodes composed of palladium-coated and palladium-filled carbon nanotubes (CNTs) were prepared and investigated for their battery performance. The full discharge of batteries showed 6-fold increase in the first discharge of the Pdfilled over the pristine CNTs and 35% increase over their Pd-coated counterparts. The Pd-filled CNTs also exhibited improved cyclability with 58 full cycles of 500 mAh·g-1 at current density of 250 mA·g-1 versus 35 and 43 cycles for pristine and Pd-coated CNTs, respectively. The effect of encapsulating the Pd catalysts inside the CNTs proved to increase the stability of the electrolyte during both discharging and charging. Voltammetry, Raman spectroscopy, XRD, UV/Vis spectroscopy, and visual inspection of the discharge products using scanning electron microscopy confirmed the increased stability of the electrolyte due catalyst shielding. The electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on carbon nanotubes (CNT) cathodes with palladium (Pd) catalyst, Pd-coated CNT and Pd-filled CNT, have been evaluated in an ether-based electrolyte solution to develop a lithium oxygen (Li−O2) battery with a high specific energy. The electrochemical properties of CNT cathodes were studied using electrochemical impedance spectroscopy (EIS). The infrared spectroscopy and SEM are employed to analyze the reaction products adsorbed on the electrode surface of the Li-O2 battery developed using Pd-coated and Pd-filled CNTs as cathode and an ether based electrolyte. vii Studies in this dissertation conclude that the use of nanocatalysts composed of palladium improved the overall performance of the Li-O2 batteries, while shielding these catalysts from direct contact with the electrolyte prolonged the life of the battery by stabilizing the electrolyte.

Indiana University-Purdue University Indianapolis (IUPUI) / Lithium based batteries have become ubiquitous with our everyday life. They have propelled a generation of smart personal electronics and electric transport. Their use is now percolating to various fields as a source of energy to facilitate the operation of devices from nanoscale to mega scale. This need for a portable energy source has led to tremendous scientific interest in this field to develop electrochemical devices like batteries with higher capacities, longer cycle life and increased safety at a low cost. To this end, the research presented in this thesis focuses on two emerging and promising technologies called lithium-oxygen (Li-O₂) and lithium-sulfur (Li-S) batteries. These batteries can offer an order of magnitude higher capacities through cheap, environmentally safe and abundant elements, namely oxygen and sulfur. The first work introduces the concept of closed system lithium-oxygen batteries wherein the cell contains the discharge product of Li-O₂ batteries namely, lithium peroxide (Li₂O₂) as the starting active material. The reversibility of this system is analyzed along with its rate performance. The possible use of such a cathode in a full cell is explored. Also, this concept is used to verify if all the lithium can be extracted from the cathode in the first charge. In the following work, lithium peroxide is chemically synthesized and deposited in a carbon nanofiber matrix. This forms a free-standing cathode that shows high reversibility. It can be cycled up to 20 times, and while using capacity control protocol, a cycle life of 50 is obtained. The cause of cell degradation and failure is also analyzed. In the work on full cell lithium-sulfur system, a novel electrolyte is developed that can support reversible lithium insertion and extraction from a graphite anode. A method to deposit solid lithium polysulde is developed for the cathode. Coupling a lithiated graphite anode with the cathode using the new electrolyte yields a full cell whose performance is characterized and its post-mortem analysis yields information on the cell failure mechanism. Although still in their developmental stages, Li-O₂ and Li-S batteries hold great promise to be the next generation of lithium batteries, and these studies make a fundamental contribution towards novel cathode and cell architecture for these batteries.

A galvanic cell converts chemical energy into electrical energy. Devices that carry out these conversions are called batteries. In batteries, generally the chemical components are contained within the device itself. If the reactants are supplied from an external source as they are consumed, the device is called a fuel cell. A fuel cell converts chemical energy into electrical energy as long as the chemicals are supplied from external reserves. The working principle of a metal-air battery involves the principles of both batteries and fuel cells. The anode of a metal-air cell is stored inside the cell, whereas O2 for the air-electrode is supplied from either atmosphere or a tank. There are several metal-air batteries available academically, which include Zn-air, Alair, Fe-air, Mg-air, Ca-air, Li-air and Na-air batteries. So far, only Zn-air battery is successfully commercialized. Li-air battery is attractive compared to other metal-air batteries because of its high theoretical energy density (11140 Wh kg-1). The energy density of Li-air battery is 3 - 5 times greater than state-of-art Li-ion battery. Li-air (or Li-O2) battery comprises Li-metal as the anode and a porous cathode. The cathode and the anode are separated by a suitable separator soaked in an organic electrolyte. Atmospheric air can enter the battery through the porous cathode. Out of the mixture of gases present in the air, only O2 is electrochemically active. For optimization purpose, most of researchers use pure O2 gas instead of air. Li-air battery is not commercialized till now because of several issues associated with it. The issues include: (i) sluggish kinetics of O2 electrode reaction, (ii) decomposition of the electrolyte during charge-discharge cycling, (iii) formation of Li dendrites, (iv) contamination by moisture, etc. Among these scientific and technical problems related to Li-O2 cell system, studies on rechargeable O2 electrode with fast kinetics of oxygen reduction reaction (ORR) during the cell discharge and oxygen evolution reaction (OER) during charge in non-aqueous electrolytes are important. In non-aqueous electrolytes, the 1-electron reduction of O2 to form superoxide (O2 -) is known to occur as the first step. (ii) Subsequently, superoxide undergoes reduction to peroxide (O2 2-) and then to oxide (O2-). The kinetics of ORR is slow in non-aqueous electrolytes. Furthermore, the reaction needs to be reversible for rechargeable Li-air batteries. In order to realize fast kinetics, a suitable catalyst is essential. The catalyst should be bifunctional for both of ORR and OER in rechargeable battery applications. Noble metal particles have been rarely investigated as catalysts for O2 electrode of Li-O2 cells. Graphene has two-dimensional planar structure with sp2 bonded carbon atoms. It has become an important electrode material owing to its high electronic conductivity and large surface area. It has been investigated for applications such as supercapacitors, Li-ion batteries, and fuel cells. Catalyst nanoparticles prepared and anchored to graphene sheets are expected to sustain discrete existence without undergoing agglomeration and therefore they possess a high catalytic stability for long term experiments as well as applications. In this context, it is intended to explore the catalytic activity of noble metal nanoparticles dispersed on reduced graphene oxide (RGO) for O2 electrode of Li-O2 cells. While a majority of the investigations reported in the thesis involves noble metal and alloy particles dispersed on RGO sheets, results on polypyrrole-RGO composite and also magnesium cobalt silicate for Li-O2 system are included. A chapter on electrochemical impedance analysis of LiMn2O4, a cathode material of Li-ion batteries, is also presented in the thesis. Introduction on electrochemical energy storage systems, in particular on Li-O2 system is provided in the 1st Chapter of the thesis. Synthesis of Ag nanoparticles anchored to RGO and catalytic activity are presented in the 2nd Chapter. Ag-RGO is prepared by insitu reduction of Ag+ ions and graphene oxide in aqueous phase by ethylene glycol as the reducing agent. The product is characterized by powder XRD, UV-VIS, IR, Raman, AFM, XPS, SEM and TEM studies. The SEM images show the layered morphology of graphene and TEM images confirm the presence of Ag nanoparticles of average diameter less than 5 nm anchored to RGO (Fig. 1a). Ag-RGO is investigated for ORR in alkaline (1 M KOH), neutral (1 M K2SO4) and non-aqueous 0.1 M tetrabutyl ammonium perchlorate in dimethyl sulphoxide (TBAP-DMSO) electrolytes. The ORR follows 4e- reduction in aqueous and 1e- reduction pathway in non-aqueous electrolytes. Li-O2 cells are assembled with Ag-RGO as (iii) Fig. 1. (a) TEM image of Ag-RGO and (b) charge-discharge voltage profiles of Li-O2 (Ag-RGO) cells. oxygen electrode catalyst in non-aqueous electrolyte (1 M LiPF6-DMSO) and subjected to charge-discharge cycling at several current densities. The discharge capacity values obtained are 11950 (11.29), 9340 (5.00), and 2780 mAh g-1 (2.47 mAh cm-2) when discharged at 0.2, 0.5, 0.8 mA cm-2, respectively (Fig. 1b). Powder XRD studies of discharged electrodes indicate the formation of Li2O2 and Li2O during the cell discharge. In addition to these studies, Na-O2 cells are also assembled with Ag-RGO in non-aqueous electrolyte. It is concluded that the chemistry Li-O2 and Na-O2 cells are similar except for the capacity values. Metal nanoparticles of Au, Pd and Ir are decorated on RGO sheets by reduction of metal ions on graphene oxide by NaBH4. Au-RGO, Pd-RGO and Ir-RGO are characterized by various physicochemical techniques. Particle size of metal nanoparticles ranges from 2 to Fig.2. Charge-discharge voltage profiles Li-O2(RGO) (i) and Li-O2(Au-RGO) (ii) cells at current density 0.3 mA cm-2. 0 2500 5000 7500 10000 12500 15000 10 nm on graphene sheets. All samples are studied for ORR in aqueous and non-aqueous electrolytes by cyclic voltammetry and rotating disk electrode experiments. Li-O2 cells are assembled in 1 M LiPF6-DMSO and discharge capacity values obtained are 3344, 8192 and 11449 mAh g-1 with Au-RGO, Pd-RGO and Ir-RGO, respectively, at 0.2 mA cm-2 current density. The results of these studies are described in Chapter 3. Synthesis and electrochemical activity of Pt-based alloy nanoparticles (Pt3Ni, Pt3Co and Pt3Fe) on RGO are presented in Chapter 4. The Pt3Ni alloy particles are prepared by simultaneous reduction of Pt4+, Ni2+ and graphene oxide by hydrazine in ethylene glycol medium. Pt3Co-RGO and Pt3Fe-RGO are also prepared similar to Pt3Ni-RGO. Formation of alloys is confirmed with XRD studies. O2 reduction reaction on Pt-alloys in non-aqueous electrolyte follows 1e- reduction to O2 -. RDE results show that Pt3Ni-RGO is a better catalyst than Pt for O2 reduction (Fig. 3). Li-O2 cells are assembled with all samples and subjected to Fig. 3. Linear sweep voltammograms of Pt3Ni-RGO, Pt3Co-RGO and Pt3Fe-RGO in 0.1 M TBAPDMSO with 1600 rpm at 10 mV s-1 scan rate. The area of GC electrode was 0.0314 cm2 with a catalyst mass of 200 μg. charge-discharge cycling at several current densities. The initial discharge capacity values obtained are 14128, 5000 and 10500 mAh g-1 with Pt3Ni-RGO, Pt3Co-RGO and Pt3Fe-RGO, respectively, as the air electrode catalysts. Polypyrrole (PPY) is an attractive conducting polymer with advantages such as high electronic conductivity and electrochemical stability. A combination of advantages of graphene and PPY composite are explained in the Chapter 5. PPY is grown on already synthesized RGO sheets by oxidative polymerization of pyrrole in an acidic PY composite is characterized by XRD and Raman spectroscopy studies. Li-O2 cells are assembled in non-aqueous electrolyte and subjected for charge-discharge cycling at different current densities. The discharge capacity value of Li-O2(PPY-RGO) cell is 3358 mAh g-1 Fig. 4. (a) Discharge-charge performance of Li-O2(PPY-RGO) cell with a current density of 0.2 mA cm-2 limiting to a capacity of 1000 mAh g-1 and (b) variation of cut-off voltages on cycling. (3.94 mAh cm-2) in the first cycle. Li-O2(PPY-RGO) cell delivers 3.7 times greater discharge capacity than Li-O2(RGO) cell. Cycling stability of Li-O2 (PPY-RGO) cell is investigated by charge-discharge cycling by limiting the capacity to 1000 mAh g-1, and the cell voltage at the end of discharge and at the end of charge are found constant at 2.75 and 4.10 V, respectively (Fig. 4 a, b). This study shows that PPY-RGO is stable in Li-O2 cells. Electrochemical impedance study shows that charge-transfer resistant is 500 Ω for freshly assembled Li- O2(PPY-RGO) cell and it decreases to 200 Ω after 1st discharge. Synthesis of magnesium cobalt silicate and its electrochemical activity are presented in Chapter 6. MgCoSiO4 is synthesized by mixed solvothermal approach and characterized by various physicochemical techniques. Cubic shaped MgCoSiO4 is investigated for oxygen evolution reaction (OER) activity in alkaline and neutral media. The current values at 0.95 versus SHE are 43, 0.18, 16 mA cm-2 on MgCoSiO4, bare carbon paper and Pt foil electrodes, respectively (Fig. 5), indicating that MgCoSiO4 is a good catalyst for OER. The onset potential for OER is 0.68 V versus SHE on MgCoSiO4 in 1 M KOH. OER activity on MgCoSiO4 is also studied in K2SO4 and phosphate buffer electrolytes. The results indicate good catalytic activity of MgCoSiO4 in neutral electrolytes also. The catalytic activity of Fig. 5. Cyclic voltammograms of bare carbon paper (i), Pt foil (ii), MgCoSiO4 coated carbon (iii) electrodes in 1 M KOH (sweep rate = 5 mV s-1, loading level = 1.15 mg, area = 0.5 cm-2). MgCoSiO4 towards ORR in aqueous and non-aqueous electrolytes is studied by RDE experiments. Li-O2 cells are assembled with bifunctional MgCoSiO4 catalyst in 1 M LiPF6- DMSO electrolyte and the discharge capacity values obtained are 7721 (8.27), 2510 (1.66) and 1053 mAh g-1 (0.92 mAh cm-2) when discharged at 0.3, 0.5 and 0.8 mA cm-2 current densities, respectively. Electrochemical impedance spectroscopy (EIS) measurements of LiMn2O4 electrode are carried out at different temperatures from -10 to 50 0C and in the potential range from 3.50 to 4.30 V, and the data are analysed in Chapter 7. In the EIS spectra recorded over the frequency range from 100 kHz to 0.01 Hz at different temperatures, there are two semicircles present in the Nyquist plot (Fig. 6a). But in 3.90 to 4.10 V versus Li/Li+(1M) potential range at low temperatures (-10 to 15 oC) range, another semicircle also appears (Fig. 6b). Impedance parameters such as solution resistant (Rs), charge-transfer resistance (Rct), doublelayer capacitance (Cdl), electronic resistance (Re) and Warburg impedance (WR), etc., are obtained by analysis of the EIS data. The variations of resistances with temperature are analysed by Arrhenius-like relationships and the apparent activation energies of the corresponding transport properties are evaluated. The values of activation energy for chargetransfer process are 0.37, 0.30 and 0.42 eV, at 3.50, 3.90 and 4.10 V versus Li/Li+(1M), respectively. The chemical diffusion coefficient of Li+ ions into LiMn2O4 calculated from EIS data. The values of diffusion coefficient calculated are in the range of 2.50 x 10-12 - 4.10 Fig. 6. Nyquist plot of impedance study of Li/LiMn2O4 cell at 3.50 V (a) and 3.90 V (b) at -10 0C. Details of the above studies are described in the thesis.

Non-aqueous metal-air (Li-O2 and Na-O2) batteries have been emerging as one of the most promising high-energy storage systems to meet the requirements for demanding applications due to their high theoretical specific energy. In the present thesis work, advanced characterization techniques are demonstrated for the exploration of metal-O2 batteries. Prominently, the electrochemical reactions occurring within the Li-O2 and Na-O2 batteries upon cycling are studied by in operando powder X-ray diffraction (XRD). In the first part, a new in operando cell with a combined form of coin cell and pouch cell is designed. In operando synchrotron radiation powder X-ray diffraction (SR-PXD) is applied to investigate the evolution of Li2O2 inside the Li-O2 cells with carbon and Ru-TiC cathodes. By quantitatively tracking the Li2O2 evolution, a two-step process during growth and oxidation is observed. This newly developed analysis technique is further applied to the Na-O2 battery system. The formation of NaO2 and the influence of the electrolyte salt are followed quantitatively by in operando SR-PXD. The results indicate that the discharge capacity of Na-O2 cells containing a weak solvating ether solvent depends heavily on the choice of the conducting salt anion, which also has impact on the growth of NaO2 particles. In addition, the stability of the discharge product in Na-O2 cells is studied. Using both ex situ and in operando XRD, the influence of sodium anode, solvent, salt and oxygen on the stability of NaO2 are quantitatively identified. These findings bring new insights into the understanding of conflicting observations of different discharge products in previous studies. In the last part, a binder-free graphene based cathode concept is developed for Li-O2 cells. The formation of discharge products and their decomposition upon charge, as well as different morphologies of the discharge products on the electrode, are demonstrated. Moreover, considering the instability of carbon based cathode materials, a new type of titanium carbide on carbon cloth cathode is designed and fabricated. With a surface modification by loading Ru nanoparticles, the titanium carbide shows enhanced oxygen reduction/evolution activity and stability. Compared with the carbon based cathode materials, titanium carbide demonstrated a higher discharge and charge efficiency.

Lithium-oxygen batteries, also known as Lithium-air batteries, could possibly revolutionize energy storage as we know. By letting lithium react with ambient oxygen gas very large theoretical energy densities are possible. However, there are several challenges remaining to be solved, such as finding suitable materials and understanding the reaction, before the lithium-oxygen battery could be commercialized. The scope of this thesis is focusing on the latter of these challenges. Efficient ion transport between the electrodes is imperative for all batteries that need high power density and energy efficiency. Here the mass transport properties of lithium ions in several different solvents was evaluated. The results showed that the lithium  mass transport in electrolytes based on the commonly used lithium-oxygen battery solvent dimethyl sulfoxide (DMSO) was very similar to that of conventional lithium-ion battery electrolytes. However, when room temperature ionic liquids were used the performance severely decreased. Addition of Li salt will effect the oxygen concentration in DMSO-based electrolytes. The choice of lithium salt influenced whether the oxygen concentration increased or decreased. At one molar salt concentration the highest oxygen solubility was 68 % larger than the lowest one. Two model systems was used to study the electrochemical reaction: A quartz crystal microbalance and a cylindrical ultramicroelectrode. The combined usage of these systems showed that during discharge soluble lithium superoxide was produced. A consequence of this was that not all discharge product ended up on the electrode surface. During discharge the cylindrical ultramicroelectrodes displayed signs of passivation that previous theory could not adequately describe. Here the passivation was explained in terms of depletion of active sites. A mechanism was also proposed. The O2 and Li+ concentration dependencies of the discharge process were evaluated by determining the reactant reaction order under kinetic and mass transport control. Under kinetic control the system showed non-integer reaction orders with that of oxygen close to 0.5 suggesting that the current determining step involves adsorption of oxygen. At higher overpotentials, at mass transport control, the reaction order of lithium and oxygen was zero and one, respectively. These results suggest that changes in oxygen concentration will influence the current more than that of lithium. During charging not all of the reaction product was removed. This caused an accumulation when several cycles was examined. The charge reaction pathway involved de-lithiation and bulk oxidation, it also showed an oxygen concentration dependence. / Litiumsyrebatteriet, även känt som litiumluftbatteriet, kan potentiellt revolutionera vårt förhållande till energilagring. Genom att låta litium reagera med syrgas från luften kan teoretiskt höga energitätheter uppnås. Dock så behöver många problem lösas, så som att hitta lämpliga elektrod- och elektrolytmaterial samt att få en ökad förståelse för reaktionsmekanismen, innan litiumsyrebatteriet kan kommersialiseras. Den här avhandlingen behandlar de sistnämnda av dessa problem. För att ett batteri ska kunna leverera hög effekttäthet och energieffektivitet krävs en effektiv jontransport mellan elektroderna. Här utvärderades masstransporten hos flera olika elektrolyter. Resultatet visade att masstransporten av litium i en litiumsyrebatterielektrolyt (baserad på dimetylsulfoxid (DMSO)) är likvärdig med en konventionell litiumjonbatterielektrolyt. När elektrolyter baserade på jonvätskor användes uppvisades väldigt stora energiförluster. När litiumsalt tillsattes påverkades lösligheten av syre i DMSO-baserade elektrolyter. Vilken sorts litiumsalt som användes påverkade om lösligheten av syre ökade eller minskade. Vid en saltkoncentration på en molar var den högsta syrelösligheten 68 \% större än den lägsta. Två olika modellsystem används för att studera den elektrokemiska reaktionen: En elektrokemisk kvartskristallmikrovåg och en cylindrisk ultramikroelektrod. Vid kombinerad användning av dessa system påvisades att löslig litiumsuperoxid bildades vid urladdningen. Följden av detta blev att endast delar av urladdningsprodukten hamnade på elektroden. Vid urladdning visade ultramikroelektroderna tecken på passivering som inte kunde beskrivas av tidigare teori. Här föreslås att passiveringen uppstår på grund av en blockering av de aktiva säten där reaktionen fortskrider. För denna process föreslås även en detaljerad mekanism. Urladdningsprocessens koncentrationsberoende utvärderades genom att bestämma reaktionsordningen för syre och litium under kinetisk- och masstransport kontroll. Under kinetisk kontroll fanns inga heltalsreaktionsordningar, för syre var reaktionsordningen nära 0.5 vilket föreslår att det reaktionssteg som bestämmer strömstorleken innefattar en adsorption av syre. Vid högre överpotentialer, då systemet var under masstransportkontroll, var reaktionsordningarna för litium och syre noll respektive ett. Detta föreslår att ändringar i syrekoncentration påverkar strömmen betydligt mer än vad det gör för litium. Under uppladdning kunde inte all reaktionsprodukt avlägsnas från elektroden. Detta ledde till en ackumulation då flera cykler studerades. Uppladdningens delsteg innefattade en delitiering följt av en oxidation av reaktionsproduktbulken. Denna process uppvisade även ett syrekoncentrationsberoende. / <p>QC 20171114</p>

The purpose of this diploma thesis is to describe the impact of compaction pressure on the electrochemical parameters of lithium-sulfur batteries. Theoretical part of this thesis contains briefly described terminology and general issues of batteries and their division. Every kind of battery is provided with a closer description of a specific battery type. A separate chapter is dedicated to lithium cells, mainly lithium-ion batteries. Considering various composition of lithium-ion batteries, this chapter deeply analyzes mostly used active materials of electrodes, used electrolytes and separators. Considering that the electrochemical principle of Li-S and Li-O batteries is different to Li-ion batteries, these accumulators of new generation are included in individual subhead. In the experimental part of this thesis are described methods used to measure electrochemical parameters of Li-S batteries. Next chapter contains description of preparing individual electrodes and their composition. Rest of the experimental part of my thesis is dedicated to the description of individual experiments and achieved results.