| 1. |
- Kanai, M, et al.
(författare)
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- 2023
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swepub:Mat__t
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| 2. |
- Benavente, Fabian, 1985-
(författare)
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Lithium-ion batteries for off-grid PV-systems
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis provides a comprehensive and detailed analysis on the effect ofthe battery operation strategy on the lifetime of commercial lithium-ionbatteries and on the economics of off-grid photovoltaic (PV)-batterysystems.Lithium-ion batteries play a key role in the transition to a fossil-freesociety. Compared to electric vehicles, stationary energy storage hasdifferent requirements for the performance and lifetime of batteries.Although optimal battery design is critical to achieve high energy densityand longer lifetime, operation plays an important role in preventingpremature performance degradation. Understanding the effects ofsuppressed demand, geographical location, and application on system lifecycle costs also enables optimal system design.Load profiles for three applications were estimated and implemented in asimulation model, along with meteorological data for three locations andthe suppressed demand (SD) effect. Using the hourly state of charge (SOC)profiles, four battery operation strategies were designed using partialcycling with different cut-off voltages and two state of charge windows(ΔSOC). Commercial cells were used for the experimental tests. After over1000 cycles a post-mortem characterization was performed.The experiments revealed the cause of premature degradation at high SOCoperation to be a combination of impedance rise in the positive electrodeand loss of lithium inventory at the negative electrode leading to decreaseof capacity. Studies on the impedance spectra of the cells using physicsbasedmodeling revealed a loss of conductivity between particles in thepositive electrode. At system level, as the SD increases, so does theoperational ΔSOC width, while the reliability of the system decreases. Wedefined the reliability as loss of power supply probability. Finally,optimization of cost and reliability, revealed that an optimal system designfavors a battery operation strategy with wider ΔSOC instead of batterylifetime.
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| 3. |
- Malmgren, Sara, 1985-
(författare)
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Insights into Li-ion Battery and Stainless Steel Interfaces Using Refined Photoelectron Spectroscopy Methodology
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- If sacrificing some of its material to form a passivating layer at the surface, materials may expand the range of environments where they can be used and further material degradation can decrease. This thesis aims to contribute with insights into passivating layers on especially Li-ion battery anodes (solid electrolyte interphase, SEI) but also on stainless steels, as well as the non-passivating Li-ion battery cathode/electrolyte interface layers (solid permeable interface, SPI). The studies have been performed using new possibilities offered by photoelectron spectroscopy techniques.Depth gradients in the SEI and SPI layers were studied by combining synchrotron-based hard and soft X-ray photoelectron spectroscopy (HAXPES and SOXPES), which was further developed for Li-ion battery investigations. Stainless steel depth profiles were acquired combining HAXPES with angle resolved X-ray photoelectron spectroscopy (ARXPS).In the Li-ion battery, organic species were more common in the outermost SEI, while some inorganic compounds were only detected in the more bulk sensitive measurements. No depth gradients were observed in the SPI. The interface between the graphite and the SEI was studied for the first time indicating lithium enrichment at the graphite surface. Furthermore, the influence of the film-forming additive propargyl methanesulphonate (PMS) on the electrode/electrolyte interfaces was studies, and cells cycled to end of life at 22°C and 55°C were compared.For stainless steels, the thicknesses of the oxide film as well as the nickel enriched metal layer underneath the oxide were determined. A similar methodology was applied to estimate the Li-ion battery SEI thickness.Finally, experiences from PES methodology work on the Li-ion battery systems are discussed aiming to facilitate further studies of the experimentally challenging electrochemically modified samples.
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