Performance of Conventional and Structural Lithium-Ion Batteries

Lithium-ion batteries have, in recent years, experienced a rapid development from small everyday devices towards hybrid electric vehicle (HEV) applications. Due to this shift in application area, the battery performance andits degradation with time are becoming increasingly important issues to besolved.In this thesis, lithium-ion batteries are investigated with focus on lifetime performance of an existing battery chemistry, and development of electrodes for so-called structural batteries. The systems are evaluated by electrochemical methods, such as cycling and electrochemical impedance spectroscopy (EIS),combined with material characterization and modeling. Lifetime performance of mesocarbon microbeads (MCMB)/LiFePO4 cells was investigated to develop an understanding of how this technology tolerates and is influenced by different conditions, such as cycling, storage and temperature.The lifetime of the LiFePO4-based cells was found to be significantly reduced by cycling at elevated temperature, almost five times shorter compared to cycle-aged cells at ambient temperature. The calendar-aged cells also showed major signs of degradation at elevated temperatures. The overall cause of aging was electrolyte decomposition which resulted in loss of cyclable lithium, i.e. capacity fade, and impedance increase. Commercially available polyacrylonitrile (PAN)-based carbon fibers were investigated, both electrochemically and mechanically, to determine their suitability as negative electrodes in structural batteries. The electrochemical performance of carbon fibers was found to be excellent compared to other negative electrode materials, especially for single or well-separated fibers. The mechanical properties, measured as changes in the tensile properties, showed that the tensile stiffness was unaffected by lithium-ion intercalation and cycling. The ultimate tensile strength, however, showed a distinct variation with state-of-charge (SOC). Overall, carbon fibers are suitable for structural battery applications.QC 20130529</p

Piezo-electrochemical effect in lithium-intercalated carbon fibres

In this paper we have conducted experiments to investigate the coupling between electrochemical and mechanical properties of lithium (Li)-intercalating carbon fibres (CFs). The results show promising potential for new functionalities of CFs for electrochemical actuation, sensing and energy harvesting. Li-intercalation at 1 C-rate in CFs subjected to a constant tensile extension induced a free reversible longitudinal expansion strain of approximately 0.30% which can be used as mechanical actuation. Varying the tensile extension of lithiated CFs resulted in a piezoelectric response of the open-circuit potential, in the range of several mV, enabling strain sensing. If the electrical potential is kept constant during a tensile extension a piezo-electrochemical current response is found with about 50% mechanical to electrical energy conversion efficiency, enabling energy harvesting.QC 20131129</p

The effect of lithium-intercalation on the mechanical properties of carbon fibres

Carbon fibres (CFs) can be used as lightweight structural electrodes since they have high specific tensile stiffness and ultimate tensile strength (UTS), and high lithium (Li)-intercalation capability. This paper investigates the relationship between the amount of intercalated Li and the changes induced in the tensile stiffness and UTS of polyacrylonitrile-based CF tows. After a few electrochemical cycles the stiffness was not degraded and independent of the measured capacity. A drop in the UTS of lithiated CFs was only partly recovered during delithiation and clearly larger at the highest measured capacities, but remained less than 40% at full charge. The reversibility of this drop with the C-rate and measured capacity supports that the fibres are not damaged, that some Li is irreversibly trapped in the delithiated CFs and that reversible strains develop in the fibre. However, the drop in the strength does not vary linearly with the measured capacity and the drop in the ultimate tensile strain remains lower than the CF longitudinal expansion at full charge. These results suggest that the loss of strength might relate to the degree of lithiation of defectives areas which govern the tensile failure mode of the CFs.QC 20140203</p

Effect of lithium-ion intercalation on the tensile properties of carbon fibres for energy storage composites

Carbon fibres can be used as structural electrodes because they have a high tensile properties-to-weight ratio and a graphitic structure which enables lithium-ion intercalation. Carbon fibre specimens were used as electrodes in laboratory cells. It was found that the fibre undergoes an ultimate tensile strength drop and an axial expansion which depend on the measured capacity. The results suggest that a tensile strain develops in the carbon fibre which is pre-stressed in tension and that this pre-stress correlates with the amount of lithiumions intercalated.QC 20150424</p

PERFORMANCE OF LITHIUM-INTERCALATED CARBONFIBRES FOR STRUCTURAL ELECTRODE APPLICATIONS

QC 20140417</p

PAN-based carbon fiber negative electrodes for structural lithium-ion batteries

Several grades of commercially-available polyacrylonitrile (PAN)-based carbon fibers have been studied for structural lithium-ion batteries to understand how the sizing, different lithiation rates and number of fibers per tow affect the available reversible capacity, when used as both current collector and electrode, for use in structural batteries. The study shows that at moderate lithiation rates, 100 mA g-1, most of the carbon fibers display a reversible capacity close to or above 100 mAh g-1 after ten full cycles. For most of the fibers, removing the sizing increased the capacity to some extent. However, the main factor affecting the measured capacity was the lithiation rate. Decreasing the current by a tenth yielded an increase of capacity of around 100 for all the tested grades. From the measurements performed in this study it is evident that carbon fibers can be used as the active negative material and current collector in structural batteries. © 2011 The Electrochemical Society.Source: Scopus. QC 20120210</p

Using songs for improvement grammatical competence and Russian as the foreign language in elementaru school

Dziesmu pielietošana gramatikas kompetences pilnveidē krievu valodas kā svešvalodas stundās pamatskolā. Dotais darbs ir veltīts gramatikas kompetences veidošanas didaktiskajām iespējām krievu valodas kā svešvalodas stundās ,piesaistot dziesmas un dziesmu tekstus . Diploma darba autors savā darbā analizē gramatikas lomu un vietu svešvalodas apguves procesā. Diplomdarbam ir divas daļas. Pirmajā daļā tiek apkopota un analizēta zinātnieku pieredze un dažādas pieejas un paņēmieni gramatikas kompetences veidošanā apgūstot svešvalodas. Praktiskajā daļā darba autors apraksta pētījuma norisi: pamata posmi, saturs un didaktiskā materiāla struktūra ,kā arī darba formas strādājot ar šo materiālu krievu valodas ka svešvalodas stundās. Darba nobeigumā atrodami autora secinājumi un bibliogrāfija. Dotais pētījums varētu piesaistīt skolotāju, metodiku un citu interesi, kuri seko līdzi mūsdienīgās svešvalodu apguves teorijas un prakses jautājumu attīstībai.The use of songs in the competence development in grammar in Russian as a foreign language lessons in primary school. The given work is dedicated to the didactic possibilities of developing grammar competence in Russian as a foreign language lessons by integrating songs and lyrics. The author of the diploma thesis analyses the role and place of grammar in the process of learning a foreign language. The diploma thesis has two parts. The first part summarises and analyses the scientific experience and various approaches and techniques in the development of grammar competence while learning foreign languages. In the practical part, the author describes the course of the research: the basic stages, content and structure of the didactic material, as well as the forms of work with this material in Russian as a foreign language lessons. At the end of the work you can find the author's conclusions and bibliography. The given research could attract the interest of teachers, methodologists and others who follow the development of modern foreign language learning theory and practice issues

Li-Ion Pouch Cells for Vehicle Applications-Studies of Water Transmission and Packing Materials

This study includes analysis of encapsulation materials from lithium-ion pouch cells and water vapour transmission rate (WVTR) measurements. WVTR measurements are performed on both fresh and environmentally stressed lithium-ion pouch cells. Capacity measurements are performed on both the fresh and the environmentally stressed battery cells to identify possible influences on electrochemical performance. Preparation of the battery cells prior to WVTR measurements includes opening of battery cells and extraction of electrode material, followed by resealing the encapsulations and adhesively mounting of gas couplings. A model describing the water diffusion through the thermal welds of the encapsulation are set up based on material analysis of the encapsulation material. Two WVTR equipments with different type of detectors are evaluated in this study. The results from the WVTR measurements show how important it is to perform this type of studies in dry environment and apply a rigorous precondition sequence before testing. Results from modelling confirm that the WVTR method has potential to be used for measurements of water diffusion into lithium-ion pouch cells. Consequently, WVTR measurements should be possible to use as a complement or alternative method to for example Karl Fisher titration.QC 20130305</p

Piezo-Electrochemical Energy Harvesting with Lithium-Intercalating Carbon Fibers

The mechanical and electrochemical properties are coupled through a piezo-electrochemical effect in Li-intercalated carbon fibers. It is demonstrated that this piezo-electrochemical effect makes it possible to harvest electrical energy from mechanical work. Continuous polyacrylonitrile-based carbon fibers that can work both as electrodes for Li-ion batteries and structural reinforcement for composites materials are used in this study. Applying a tensile force to carbon fiber bundles used as Li-intercalating electrodes results in a response of the electrode potential of a few millivolts which allows, at low current densities, lithiation at higher electrode potential than delithiation. More electrical energy is thereby released from the cell at discharge than provided at charge, harvesting energy from the mechanical work of the applied force. The measured harvested specific electrical power is in the order of 1 muW/g for current densities in the order of 1 mA/g, but this has a potential of being increased significantly.QC 20150713</p