| 1. |
- Aktekin, Burak
(författare)
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The Electrochemistry of LiNi0.5-xMn1.5+xO4-δ in Li-ion Batteries : Structure, Side-reactions and Cross-talk
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of Li-ion batteries in portable electronic products is today widespread and on-going research is extensively dedicated to improve their performance and energy density for use in electric vehicles. The largest contribution to the overall cell weight comes from the positive electrode material, and improvements regarding this component thereby render a high potential for the development of these types of batteries. A promising candidate is LiNi0.5Mn1.5O4 (LMNO), which offers both high power capability and energy density. However, the instability of conventional electrolytes at the high operating potential (~4.7 V vs. Li+/Li) associated with this electrode material currently prevents its use in commercial applications.This thesis work aims to investigate practical approaches which have the potential of overcoming issues related to fast degradation of LNMO-based batteries. This, in turn, necessitates a comprehensive understanding of degradation mechanisms. First, the effect of a well-known electrolyte additive, fluoroethylene carbonate is investigated in LNMO-Li4Ti5O12 (LTO) cells with a focus on the positive electrode. Relatively poor cycling performance is found with 5 wt% additive while 1 wt% additive does not show a significant difference as compared to additive-free electrolytes. Second, a more fundamental study is performed to understand the effect of capacity fading mechanisms contributing to overall cell failure in high-voltage based full-cells. Electrochemical characterization of LNMO-LTO cells in different configurations show how important the electrode interactions (cross-talk) can be for the overall cell behaviour. Unexpectedly fast capacity fading at elevated temperatures is found to originate from a high sensitivity of LTO to cross-talk.Third, in situ studies of LNMO are conducted with neutron diffraction and electron microscopy. These show that the oxygen release is not directly related to cation disordering. Moreover, microstructural changes upon heating are observed. These findings suggest new sample preparation strategies, which allow the control of cation disorder without oxygen loss. Following this guidance, ordered and disordered samples with the same oxygen content are prepared. The negative effect of ordering on electrochemical performance is investigated and changes in bulk electronic structure following cycling are found in ordered samples, accompanied by thick surface films on surface and rock-salt phase domains near surface.
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| 2. |
- Johansson, Isabell L., 1994-
(författare)
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The Art of Cycling – Polymer Electrolytes at Extreme Conditions
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the rapid development of batteries for applications like electric vehicles and energy storage devices, it is essential to design and develop batteries with improved safety, long cycle life, and high energy density. To achieve this goal, the development and improvement of solid-state batteries, containing solid polymer electrolytes, is a promising solution. The interest in polymer electrolytes is primarily owed to their proposed compatibility with high temperatures and reactive electrodes, such as metallic lithium, and their ability to withstand higher temperatures than traditional liquid electrolytes. Cycling polymer electrolytes at high temperature and with high-voltage cathodes, such as lithium-nickel-manganese-cobalt-oxide (NMC) involves a combination of high chemical, electrochemical, and mechanical stability, as well as the understanding of how to achieve these properties.This thesis provides an overview of some challenges and possibilities of cycling batteries with polymer electrolytes at high temperatures and with high-voltage cathodes. With a focus on the stability of the polymer electrolyte, the effect of changing the polymer host material, the electrolyte salt, and the introduction of additives for enhanced mechanical stability or electrochemical stability, were all evaluated by both standard techniques and techniques developed for polymer electrolytes. Long-term cycling at high temperature was achieved for a poly(ε-caprolactone-co-trimethylene carbonate) (PCL-PTMC) electrolyte by crosslinking additives that increase the mechanical stability of the polymer electrolyte; however, the cycling with high-voltage cathodes also required a high electrochemical stability of the polymer electrolyte. With the techniques developed herein, such as cut-off increase cell cycling, the electrochemical stability of PCL-PTMC was evaluated. By introducing zwitterionic additives to PCL-PTMC, the cycling performance with NMC was enhanced and the enhancement proved to stem from prevention of electrolyte salt decomposition. Finally, by changing the electrolyte salt, it was found that cycling with NMC was possible for PCL-PTMC below its oxidative degradation potential, as long as the electrolyte had an ionic conductivity that was high enough. By utilizing additives, the long-term stability and electrochemical stability toward NMC was also improved. Overall, cycling solid polymer electrolytes at high temperatures and with high-voltage cathodes presents a unique set of challenges, which require that the electrochemical stability of the electrolyte is accurately described, and that the following properties are high: ionic conductivity, electrochemical and mechanical stability; all of which can be improved by utilizing additives in the polymer electrolyte.
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| 3. |
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| 4. |
- Shabani, Masoume
(författare)
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Techno-economic viability of battery storage for residential applications
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Battery storage has emerged as a promising solution in various energy systems. However, challenges exist regarding the viability of batteries in practical stationary applications. Factors such as the capital and operational costs, relatively short lifetime, and battery degradation are among crucial factors which have significant impact on battery profitability. To make batteries more viable technology, effective battery management is a necessity. However, there are multiple critical factors which need to be addressed for effective battery utilization and management in real-life applications under dynamic operational conditions.In this thesis, different battery modelling approaches within battery operational management are proposed. Each proposed scenario consists of a set of specific methods for the estimation of battery performance, capacity degradation, remaining useful life, state-of-charge, state-of-health, and state-of- power.Moreover, the study explores strategies for efficient battery utilization to maximize sustained profitability. Accordingly, the study deals with 32 different state-of-charge operating control strategies as well as different charge/discharge rates (low, moderate, high) to evaluate their impact on techno-economic profitability of a battery system in a grid-connected residential application. Moreover, two day-ahead and optimization-based operation scheduling strategies to maximize battery profitability are proposed. Each scenario employs unique approaches to make optimal decisions for optimal battery utilization. The first scenario aims to optimize short-term profitability by prioritizing revenue gains. Conversely, the second scenario proposes a smart strategy capable of making intelligent decisions on a wide range of decision-variables to simultaneously maximize daily revenue and minimize daily degradation costs.The key findings reveal that overlooking or simplifying assumptions about multiple critical aspects of battery behavior led to an improper battery management system in practical applications under dynamic operational conditions. Selecting a proper state-of-charge control strategy positively affects the profitability in which alteration of the allowable SOC window from (40%–90%) to (10%–60%) increase the battery lifetime from 10.2 years to 14 years leading to 31.6% improvement in net present value. The key findings showcase how a smart battery scheduling strategy that strike optimal balance between revenue and degradation achieves impressive profit (18-20 €/kWh/year), short payback (7.5 years), and extended lifespan (12.5 years), contrasting revenue-focused scenarios, ensuring sustained profitability for battery owners in residential applications. The findings offer valuable insights for decision-makers, enabling informed strategic choices and profitable solutions.
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| 5. |
- Xu, Chao, 1988-
(författare)
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Non-aqueous Electrolytes and Interfacial Chemistry in Lithium-ion Batteries
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lithium-ion battery (LIB) technology is currently the most promising candidate for power sources in applications such as portable electronics and electric vehicles. In today's state-of-the-art LIBs, non-aqueous electrolytes are the most widely used family of electrolytes. In the present thesis work, efforts are devoted to improve the conventional LiPF6-based electrolytes with additives, as well as to develop alternative lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI)-based electrolytes for silicon anodes. In addition, electrode/electrolyte interfacial chemistries in such battery systems are extensively investigated.Two additives, LiTDI and fluoroethylene carbonate (FEC), are evaluated individually for conventional LiPF6-based electrolytes combined with various electrode materials. Introduction of each of the two additives leads to improved battery performance, although the underlying mechanisms are rather different. The LiTDI additive is able to scavenge moisture in the electrolyte, and as a result, enhance the chemical stability of LiPF6-based electrolytes even at extreme conditions such as storage under high moisture content and at elevated temperatures. In addition, it is demonstrated that LiTDI significantly influences the electrode/electrolyte interfaces in NMC/Li and NMC/graphite cells. On the other hand, FEC promotes electrode/electrolyte interfacial stability via formation of a stable solid electrolyte interphase (SEI) layer, which consists of FEC-derivatives such as LiF and polycarbonates in particular.Moreover, LiTDI-based electrolytes are developed as an alternative to LiPF6 electrolytes for silicon anodes. Due to severe salt and solvent degradation, silicon anodes with the LiTDI-baseline electrolyte showed rather poor electrochemical performance. However, with the SEI-forming additives of FEC and VC, the cycling performance of such battery system is greatly improved, owing to a stabilized electrode/electrolyte interface.This thesis work highlights that cooperation of appropriate electrolyte additives is an effective yet simple approach to enhance battery performance, and in addition, that the interfacial chemistries are of particular importance to deeply understand battery behavior.
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| 6. |
- Andersson, Rassmus
(författare)
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Discovering new ground in ion transport: Exploring coordination effects in polymer electrolytes : – From method development to battery implementation
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The exponentially increasing demand for portable and stationary energy storage devices is pushing the development of lithium-ion batteries (LIBs). This requires safer and more sustainable electrolytes where solid polymer electrolytes (SPEs) are a viable alternative to the flammable liquid electrolytes used nowadays. However, SPEs are characterized by poor ionic conductivity compared to their liquid equivalents, preventing large-scale implementation. Furthermore, to meet the increasing production rate of batteries, alternative battery chemistries based on more abundant resources than Li are explored. To address these matters, a fundamental understanding of ion transport in SPEs for a range of relevant cations is vital in the development process.In the thesis, the ion transport is explored on a fundamental level for Li+ in addition to cations “beyond Li” such as Na+, K+ and Mg2+ in polyether-, polyester- and polycarbonate-based SPEs, where the core encompasses the connection between the ion coordination strength and the transference number (T+). New methods to investigate these properties have been developed especially targeting these more challenging cations. To study the ion coordination strength, two qualitative and one quantitative methods based on NMR and FTIR, are presented. In addition, eNMR and EIS have been combined to determine T+.Regardless of the cation investigated, the strongest coordination was observed for polyethylene oxide, stemming from its chelating effect on the cations. In contrast, poly(trimethylene carbonate) exhibited the weakest coordination, while poly(ε-caprolactone) fell in between. A direct correlation between the coordination strength and the T+ was also recognized, where strong interactions are accompanied by low T+ and vice versa. Moreover, the divalent Mg2+ displayed particularly interesting transport characteristics, where the [MgTFSI]+ speciation appears to be a large contributor to the net Mg mobility. Lastly, the outcome of incorporating an ion-conducting polymer as the soft segment in polyurethanes is that the transport mechanism of the pure SPE remains. In combination with sustained long-term cycling in lithium metal batteries, the polyurethanes illustrate opportunities for new designs by adjusting the soft segments. Similarly, the properties of poly(1-oxoheptamethylene) can be controlled by tuning its saturation degree, which is crucial for the ion conduction and mechanical properties in lithium metal batteries, since it highly affects the crystallinity and the crosslinking of the systems.In summary, this thesis contributes toward the understanding of ion transport in systems belonging to “next-generation” batteries, where SPEs for lithium-metal batteries as well as for cations “beyond Li” are considered to play an important part.
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| 7. |
- Bergfelt, Andreas, 1983-
(författare)
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Block Copolymer Electrolytes : Polymers for Solid-State Lithium Batteries
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of solid polymer electrolytes (SPEs) for lithium battery devices is a rapidly growing research area. The liquid electrolytes that are used today are inflammable and harmful towards the battery components. The adoption of SPEs could drastically improve this situation, but they still suffer from a too low performance at ambient temperatures for most practical applications. However, by increasing the operating temperature to between 60 °C and 90 °C, the electrolyte performance can be drastically increased. The drawback of this approach, partly, is that parasitic side reactions become noticeable at these elevated temperatures, thus affecting battery lifetime and performance. Furthermore, the ionically conductive polymer loses its mechanical integrity, thus triggering a need for an external separator in the battery device.One way of combining both mechanical properties and electrochemical performance is to design block copolymer (BCP) electrolytes, that is, polymers that are tailored to combine one ionic conductive block with a mechanical block, into one polymer. The hypothesis is that the BCP electrolytes should self-assemble into well-defined microphase separated regions in order to maximize the block properties. By varying monomer composition and structure of the BCP, it is possible to design electrolytes with different battery device performance. In Paper I and Paper II two types of methacrylate-based triblock copolymers with different mechanical blocks were synthesized, in order to evaluate morphology, electrochemical performance, and battery performance. In Paper III and Paper IV a different strategy was adopted, with a focus on diblock copolymers. In this strategy, the ethylene oxide was replaced by poly(e-caprolactone) and poly(trimethylene carbonate) as the lithium-ion dissolving group. The investigated mechanical blocks in these studies were poly(benzyl methacrylate) and polystyrene. The battery performance for these electrolytes was superior to the methacrylate-based battery devices, thus resulting in stable battery cycling at 40 °C and 30 °C.
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| 8. |
- Chien, Yu-Chuan, 1990-
(författare)
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Operando Characterisation of Lithium–Sulfur Batteries
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lithium–sulfur (Li–S) batteries have been under the spotlight of research on electrochemical energy storage systems, primarily owing to their high theoretical specific energy (2552 Wh kg-1). So far, Li–S cells on the market have presented a specific energy of 400 Wh kg-1, which is superior to many commercial alternatives, but far below the theoretical value. At the same time, Li–S batteries encounter other problems that are generally not associated with the standard Li-ion batteries, such as low utilisation rate of active materials and short cycle life. These often originate from the unique catholyte nature and/or the low reversibility of the metallic Li electrode.The dissolution and precipitation of elemental sulfur and lithium sulfide in the positive electrode are here investigated by operando X-ray diffraction (XRD) and small-angle neutron/X-ray scattering (SANS/SAXS) coupled with the Intermittent Current Interruption (ICI) method. The real-time internal and diffusion resistances are correlated to the kinetics of the precipitation of the crystalline species by operando XRD. Through operando SANS and SAXS, the formation of crystalline and amorphous solid-state discharge products and the compositional variation of catholyte inside the mesopores are linked to features in the resistance profiles. These studies indicate that the ionic transport limitation inside the positive electrode is the cause for the low sulfur utilisation during battery discharge.To examine the impact of the repetitive precipitation on the functionality of the positive sulfur electrode, a method based on electrochemical impedance spectroscopy (EIS) was developed to track the electrochemically active surface area of the carbon matrix in-situ over extensive cycling. The investigation found no progressive passivation on the positive electrode despite the rapid decrease in specific discharge capacity. Additionally, a novel three-electrode setup for Li–S cells reveals a faster growth of the resistance on the metallic Li electrode along cycling. These findings suggest that primarily the negative electrode limits the cycle life. Through providing the mechanistic insights of operational Li–S cells, this thesis demonstrates the value of simultaneous electrochemical and materials characterisations for understanding the complex Li–S system.
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| 9. |
- Ebadi, Mahsa
(författare)
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Modelling the Molecular World of Electrolytes and Interfaces : Delving into Li-Metal Batteries
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lithium metal batteries (LMBs) are potential candidates for powering portable electronic devices and for electromobility. However, utilizing the reactive Li metal electrode means tackling serious challenges in terms of safety risks. A better understanding of electrolytes and solid electrolyte interphase (SEI) formation are highly important in order to improve these issues.In this thesis, density functional theory (DFT) and molecular dynamics (MD) are used to explore novel electrolyte systems and the interfacial chemistry of electrolyte/Li metal surfaces. In the first part, the electronic structure and possible decompositions pathways of organic carbonates at the Li metal surface are investigated, which provide information about initial SEI formation. Computed X-ray photoelectron spectroscopy (XPS) for these interfacial compounds is used as a tool to find likely electrolyte decomposition pathways and are supported by direct comparison with the experimental results. The electronic structure and computed XPS spectra of electrolyte solvents and the LiNO3 additive on Li metal by DFT provide atomistic insights into the interphase layer.Solid polymer electrolytes (SPEs) are promising electrolytes to be used with the Li metal electrode. In the second part of the thesis, MD simulations of poly(ethylene oxide) (PEO) doped with LiTFSI salt/Li metal interface demonstrate the impact of the surface on the structure and dynamics of the electrolyte. A new interfacial potential model for MD simulations is also developed for the interactions at the SPE/metal interface, which can better capture this chemical interplay. Moreover, the approach to improve the ionic conductivity of SPEs by adding side-chains to the backbone of polymers is scrutinized through MD simulations of the poly(trimethylene carbonate) (PTMC) system. While providing polymer flexibility, a hindering effects of the side-chains on Li+ ion diffusions through reduced coordination site connectivity is observed.In the final part, different polymer hosts interacting with Li metal are explored, and rapid decomposition of polycarbonates and polyester on the surface is seen. The complexes of these polymers with LiTFSI and LiFSI showed significant changes in the computed electrochemical stability window and salt degradations. Lastly, Li2O was obtained by DFT calculations as a thermodynamically stable layer on the surface of the Li metal oxidized by PEO.The modelling studies performed in this thesis highlight the applicability of these techniques in order to probe the SEI and electrolyte properties in LMBs at the atomistic level.
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| 10. |
- Liu, Lianlian, 1988-
(författare)
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Renewable and Scalable Energy Storage Materials Derived from Quinones in Biomass
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Currently there is an urgent need to reduce the use of fossil fuels, and efficient sustainable energy harvesters from sun and wind have been developed and are widely used for electricity generation. Storage of electrical energy is accordingly necessary to accommodate the time varying supply of wind and solar electricity. Quinones (Q) are attractive as energy storage materials due to their high theoretical charge density and the renewable and abundant source – biomass. Plant-based biomass materials – such as lignin and humic acids – contain redox active Q-groups that potentially could be used for electricity storage instead of simply burning the biomass, which releases CO2, CH4, NOx, and SOx. Lignin accounts for 20-30% of the biomass weight and contains a sizable fraction of Q-structures. However, utilization of lignin for large scale energy storage is still a challenging task, as lignin is electrically insulating and conductive materials are required to get access to the generated electrons in the bulk. Various relatively expensive materials, such as conductive polymers and various carbon materials (carbon nanotubes, active carbon, graphene, etc.) have been combined with lignin, resulting in hybrid materials for energy storage. However, as the scale required for production of charge storage devices is huge it is of outmost importance to reduce the cost and therefore investigate low-cost conductive materials. In this thesis, common graphite flakes are combined with the lignin derivative lignosulphonate (LS) via a solvent free ball-milling process, followed by treatment with water and resulting in a paste that can be processed into electrodes. Similarly, humic acid derived from peat, lignite that contains a large amount of Q-groups is also fabricated into electrode with graphite via the ball-milling process. In order to further reduce the impact on environment during the extraction of Q-materials from biomass, barks that contain as much as 30% of lignin are directly used for energy storage via co-milling with pristine graphite to generate the biomass/graphite hybrid material electrodes. However, larger weight fraction of Q are required to further improve the electrochemical performance of these electrodes and Q chemicals (QCs) that also originate from biomass are introduced to fabricate the QCs/graphite electrodes with an increased capacity. Additionally, self-discharge mechanism is studied on the LS/graphite hybrid material electrodes, which provides instructions to achieve a low self-discharge rate.Overall, this study has brought us one step forward on the establishing of scalable, sustainable, and cost-effective energy storage systems using aqueous electrolytes.
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