| 1. |
- Le Pham, Phuong Nam, et al.
(författare)
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Potassium-ion batteries using KFSI/DME electrolytes: Implications of cation solvation on the K + -graphite (co-)intercalation mechanism
- 2022
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Ingår i: Energy Storage Materials. - : Elsevier BV. - 2405-8297. ; 45, s. 291-300
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Tidskriftsartikel (refereegranskat)abstract
- Recently potassium-ion batteries have been proposed as a promising next generation battery technology owing to cost effectiveness and a wide range of electrode materials as well as electrolytes available. Potassium bis(fluorosulfonyl)imide (KFSI) in monoglyme (DME) is one potential electrolyte, wherein the K+ solvation heavily depends on the salt concentration and strongly affects the electrochemistry. Pure K+ intercalation occurs for highly concentrated electrolytes (HCEs), while co-intercalation is dominant for less concentrated electrolytes. The mechanisms are easily distinguished by their galvanostatic curves as well as by operando XRD. Here Raman spectroscopy coupled with computational chemistry is used to provide in-depth knowledge about the cation solvation for a wide concentration range, all the way up to 5 M KFSI in DME. Starting from pure DME experimental and computed Raman spectra provides a detailed conformational assignment enabling us to calculate the solvation number (SN) of K+ by DME as a function of salt concentration for all the electrolytes. For low to medium KFSI concentrations, the SN is approximately constant, ca. 2.7, and/as there is a surplus of DME solvent available, while for HCEs, with much less DME available, the SN is <2. This reduced SN results in a thermodynamically more favored desolvation at the graphite surface, leading to intercalation, as compared to the higher SN of conventional electrolytes leading to co-intercalation, as observed also by electrochemical cycling.
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| 2. |
- Flores, Eibar, 1990, et al.
(författare)
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Solvation structure in dilute to highly concentrated electrolytes for lithium-ion and sodium-ion batteries
- 2017
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 233, s. 134-141
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Tidskriftsartikel (refereegranskat)abstract
- The solvation structure of several lithium and sodium based electrolytes are explored as a function of salt concentration over a wide range via a detailed PM7 computational study. The cation coordination shells are found to be well-defined and solvent rich for dilute electrolytes, while disordered and anion rich for the more concentrated electrolytes. The Na-based electrolytes display larger cation coordination shells with a more pronounced presence of fluorine as compared to the Li-based electrolytes. The origins of the structural differences are discussed as well as their consequences for properties of battery electrolytes and battery usage-especially targeting the current large interest in highly concentrated electrolytes.
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| 3. |
- Franko, Christopher J., et al.
(författare)
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Concentration Dependent Solution Structure and Transport Mechanism in High Voltage LiTFSI-Adiponitrile Electrolytes
- 2020
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 1945-7111 .- 0013-4651. ; 167:16
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Tidskriftsartikel (refereegranskat)abstract
- The physiochemical properties of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in adiponitrile (ADN) electrolytes were explored as a function of concentration. The phase diagram and ionic conductivity plots show a distinct relationship between the eutectic composition of the electrolyte and the concentration of maximum ionic conductivity in the 25 degrees C isotherm. We propose a structure-based explanation for the variation of electrolyte ionic conductivity with LiTFSI concentration, where the eutectic concentration is a transitionary region at which the structure changes from solvated contact ion pairs to extended units of [Li-z(ADN)(x)TFSIy](z-y) aggregates. It is found through diffusion coefficient measurements using pulsed-field gradient (PFG) NMR that both D-Li/D-TFSI and D-Li/D-ADN increase with concentration until 2.9 M, where after Li+ becomes the fastest diffusing species, suggesting that ion hopping becomes the dominant transport mechanism for Li+. Variable diffusion-time (Delta) PFG NMR is used to track this evolution of the ion transport mechanism. A differentiation in Li+ transport between the micro and bulk levels that increases with concentration was observed. It is proposed that ion hopping within [Li-z(ADN)(x)TFSIy](z-y) aggregates dominates the micro-scale, while the bulk-scale is governed by vehicular transport. Lastly, we demonstrate that LiTFSI in ADN is a suitable electrolyte system for use in Li-O-2 cells.
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| 4. |
- Lindberg, Jonas, et al.
(författare)
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Li Salt Anion Effect on O-2 Solubility in an Li-O-2 Battery
- 2018
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:4, s. 1913-1920
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Tidskriftsartikel (refereegranskat)abstract
- For the promising Li-O-2 battery to be commercialized, further understanding of its constituents is needed. This study deals with the role of O-2 in Li-O-2 batteries, both its influence on electrochemical performance and its solubility in lithium-salt-containing dimethyl sulfoxide (DMSO) electrolytes. Experimentally, the electrochemical performance was evaluated using cylindrical ultramicroelectrodes. Two independent techniques, using a mass spectrometer and an optical sensor, were used to evaluate the O-2 solubility, expressed as Henry's constant. Furthermore, the ionic conductivity, dynamic viscosity, and density were also measured. Density functional theory calculations were made of the interaction energy between O-2 and the different species in the electrolytes. When varying O-2 partial pressure, the current was larger at high pressures confirming that the O-2 concentration is of key importance when studying the kinetics of this system. Compared with neat DMSO, the O-2 solubility increased with addition of LiTFSI and decreased with addition of LiClO4, indicating that the salt influences the solubility. This solubility trend is best explained in terms of apparent molar volume and interaction energy between O-2 and the salt anion. In conclusion, this study shows the importance of O-2 concentration, not just its partial pressure, and that the choice of Li salt can make this concentration increase or decrease.
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| 5. |
- Ortiz-Vitoriano, N., et al.
(författare)
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Unlocking the role of electrolyte concentration for Na-O 2 batteries
- 2024
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Ingår i: Energy Storage Materials. - 2405-8297. ; 70
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Tidskriftsartikel (refereegranskat)abstract
- Na-O2 batteries have attracted great interest in recent years mainly due to their high energy density, in theory having prospects to outperform the commercialized lithium-ion batteries. In the quest for optimization, a recently explored approach is to use highly concentrated electrolytes (HCEs). The knowledge of molecular level of solvation as function of electrolyte concentration and its impact on Na-O2 battery performance is, however, still very limited. In this work, experimental and computational methods are used to characterize the cation solvation and when the emergence of anions into the cation first solvation shell occurs, which affects the de-solvation process and formation of discharge products. Furthermore, the solid electrolyte interphase (SEI) formed using HCEs demonstrates presence of anion fragments, with poorer protection of the Na metal anode. Moreover, the use of HCEs is also linked to lowered capacity, possibly due to a decrease in the size of the cubic-shaped discharge products as the electrolyte concentration increases, causing clogging of the pores of the air cathode. Thus, increasing the electrolyte salt concentration seems to have a detrimental effect on the cyclability of Na-O2 batteries. Instead, electrolytes with a lower than conventional salt concentration show the best performance, which highlights the importance of carefully tuning the cation solvation alongside overall physico-chemical properties to enhance battery performance.
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| 6. |
- Åvall, Gustav, 1988, et al.
(författare)
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A novel approach to ligand-exchange rates applied to lithium-ion battery and sodium-ion battery electrolytes
- 2020
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 152:23
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Tidskriftsartikel (refereegranskat)abstract
- A novel approach based on analyzing the forces and velocities of solvents and anions to compute ligand-exchange rates is here presented and applied to lithium-ion battery (LIB) and sodium-ion battery (SIB) electrolytes. By using ab initio molecular dynamics generated data, we find the ligand-exchange rates to increase as functions of electrolyte salt concentration and to be higher in SIB electrolytes as compared to LIB electrolytes. This indicates both that Na+ transport will be more non-vehicular in nature and have improved kinetics vs Li+, and that increasing the salt concentration is beneficial. The systems studied were basically the first cation solvation shells of Li/NaPF6 in propylene carbonate and acetonitrile using three solvent to salt ratios. Overall, the solvation shells are solvent rich at low salt concentrations, and as functions of concentration, the solvents are replaced by anions. As the SIB electrolytes display higher cation coordination and solvation numbers, we also expect an earlier onset of highly concentrated electrolyte behavior for SIB than LIB electrolytes. These observations should all have an impact on the design of electrolytes for optimal bulk properties, but also be useful with respect to interfacial dynamics.
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| 7. |
- Åvall, Gustav, 1988, et al.
(författare)
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Highly Concentrated Electrolytes: Electrochemical and Physicochemical Characteristics of LiPF6 in Propylene Carbonate Solutions
- 2021
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 1945-7111 .- 0013-4651. ; 168:5
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Tidskriftsartikel (refereegranskat)abstract
- Highly concentrated electrolytes (HCEs) based on LiPF6 in propylene carbonate (PC) have been examined as lithium-ion battery electrolytes. These HCEs have lower ionic conductivities and higher viscosities than ethylene carbonate (EC) electrolytes with 1.2 M LiPF6, but they have higher Li+ ion transference numbers. Electrochemical cycling behaviour of LiNi0.8C0.015Al0.05O2//graphite cells with 3.2 M LiPF6 in PC resembles that of cells with EC-based electrolytes; the HCE cells have higher impedance, which can be lowered by increasing test temperature. By employing Raman and infrared spectroscopy, combined with density functional theory and ab initio molecular dynamics simulations, we reveal that the Li+ solvation structure and speciation are key factors that determine cell performance. Two distinct regimes are observed as a function of salt concentration-in the conventional regime, the solvation number (SN) is mostly constant, while in the HCE regime it decreases linearly. Graphite exfoliation is suppressed only at very high salt concentrations (>2.4 M), where [PC](free)/[Li+] < 1 and [PF6-](free) > [PC](free). Results from the Advanced Electrolyte Model indicate that Li+ desolvation improves at higher LiPF6 concentrations, thereby mitigating PC co-intercalation into the graphite. However, Li+ ion transport is hindered in the HCEs, which increases impedance at both the oxide-positive and graphite-negative electrodes.
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| 8. |
- Åvall, Gustav, 1988
(författare)
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Modelling of Battery Electrolyte Interactions
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The rechargeable lithium-ion battery (LIB), powering our portable electronics, has transformed our everyday lives. Even though the success of the LIB there is a need for next generation batteries, due to a lack of abundant lithium and a need for greater performance and sustainable chemistries, in order to move towards a sustainable society with applications such as hybrid and electrical vehicles (EVs) and large scale energy storage for solar and wind power. Therefore, there is a large interest in various next generation batteries, such as sodium-ion, Li-S, and Li-air batteries. In this thesis the structure of Li+ and Na+ solvation shells, as functions of salt concentrations, is studied using a semi-empirical method. Overall, this shows that: i) The first solvation shell of the Na-ion is larger and more disordered than the Li-ion first solvation shell, ii) The coordination number (CN) remain quite constant as a function of concentration, while the disorder, as measured by the variance of the CN, increases with concentration, and iii) The choice of solvent influences the disorder. Moreover, the interaction of O2 with several anions is computed, showing a correlation between the interaction energy and the O2 solubility, with application to Li-air batteries. Finally, a novel approach employing ab initio molecular dynamics to study solvation shell dynamics is presented.
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| 9. |
- Åvall, Gustav, 1988, et al.
(författare)
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Sodium-Ion Battery Electrolytes: Modeling and Simulations
- 2018
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Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6840 .- 1614-6832. ; 8:17
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Forskningsöversikt (refereegranskat)abstract
- The authors review the efforts made from a modeling and simulation perspective in order to assist both the fundamental understanding as well as the development of higher performance sodium-ion battery (SIB) electrolytes. Depending on the type of the electrolyte studied, liquid, ionic liquid, polymer, glass, solid-state, etc., the simulation methods applied and the research questions in focus differ, but all contribute to more rational progress. Furthermore, the authors create cases of meta-analysis using literature data. A historical perspective is applied and the focus clearly is on more recent work and novel electrolyte materials. Finally, the authors outline a few prospective areas for where SIB electrolyte simulations can/should be extended for maximum impact in the field.
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| 10. |
- Åvall, Gustav, 1988
(författare)
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Structure and Dynamics in Liquid Battery Electrolytes
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The introduction of Sony’s rechargeable lithium-ion battery in 1991 sparked a transformation of our everyday life, enabling wide-spread use of portable electronics, such as smartphones and laptops. Furthermore, in recent years the increased usage of electrical vehicles and the on-going change to transient renewable energy sources has created a large interest in cheaper, safer, more sustainable, long-lasting and energy denser batteries. Next generation batteries – batteries beyond the traditional lithium-ion battery chemistries – offers possible routes towards the for-mentioned sought performance, societal and economical improvements. In this thesis several next generation battery concepts are studied. In particular, i) the sodium-ion battery, offering similar energy densities to that of the modern-day lithium-ion battery, but showing better power performance, is cheaper, more sustainable and safer, and ii) highly concentrated electrolytes, enabling higher energy densities, improved safety features, and improved cycling stability, are studied. Several of the improvements in safety and performance seen in these next generation battery technologies stem from the local environment in the electrolyte. In this work I present a comprehensive study of the local cationic environment in several next generation battery electrolytes employing computational methods such as semi-empirical methods, density functional theory, and ab initio molecular dynamics. Furthermore, novel methods for studying the dynamics of the solvation shell are presented. The results of these studies are compared to what I and others have found in conventional lithium-ion battery electrolytes, and the connection between the local electrolyte structure and dynamics and the macroscopic electrolyte and battery properties is discussed.
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