| 1. |
- Eliasen, K. L., et al.
(författare)
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High-frequency dynamics and test of the shoving model for the glass-forming ionic liquid Pyr14-TFSI
- 2021
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Ingår i: Physical Review Materials. - 2475-9953. ; 5:6
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Tidskriftsartikel (refereegranskat)abstract
- In studies of glass-forming liquids, one of the important questions is to understand to which degree chemically different classes of liquids have the same type of dynamics. In this context, room-temperature ionic liquids are interesting because they exhibit both van der Waals and Coulomb interactions. In this work we study the α relaxation and faster relaxation dynamics in the room-temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14-TFSI). The paper presents quasielastic neutron and shear mechanical spectroscopy data measured over seven decades in frequency (10-3-104 Hz). The use of these two methods in combination reveal the α relaxation and four separate, faster modes. Two of these faster modes, based on the partial deuterations, can be assigned to the methyl group and the methyl end of the butyl chain of the cation. The neutron data are also used to determine the mean-square displacement (MSD) on the nanosecond timescale. It is shown that the temperature dependence of the MSD can account for the super-Arrhenius behavior of the α relaxation as predicted by the shoving model [Dyre, Rev. Mod. Phys. 78, 953 (2006)RMPHAT0034-686110.1103/RevModPhys.78.953], similarly to what is seen in simpler glass-forming liquids.
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| 2. |
- Hansen, Henriette Wase, 1988, et al.
(författare)
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Density scaling of structure and dynamics of an ionic liquid
- 2020
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 22:25, s. 14169-14176
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Tidskriftsartikel (refereegranskat)abstract
- Room temperature ionic liquids are salts with low melting points achieved by employing bulky and asymmetrical ions. The molecular design leads to apolar and polar parts as well as the presence of competing Coulomb and van der Waals interactions giving rise to nano-scale structure, e.g. charge ordering. In this paper we address the question of how these nano-scale structures influence transport properties and dynamics on different timescales. We apply pressure and temperature as control parameters and investigate the structure factor, charge transport, microscopic alpha relaxation and phonon dynamics in the phase diagram of an ionic liquid. Including viscosity and self diffusion data from literature we find that all the dynamic and transport variables studied follow the same density scaling, i.e. they all depend on the scaling variable Γ = ργ/T, with γ = 2.8. The molecular nearest neighbor structure is found to follow a density scaling identical to that of the dynamics, while this is not the case for the charge ordering, indicating that the charge ordering has little influence on the investigated dynamics.
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| 3. |
- Lundin, Filippa, 1992, et al.
(författare)
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Ion Dynamics and Nanostructures of Diluted Ionic Liquid Electrolytes
- 2022
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:38, s. 16262-16271
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Tidskriftsartikel (refereegranskat)abstract
- Diluted ionic liquid electrolytes are promising candidates in next-generation batteries enabling the implementation of lithium metal anodes. The diluent should fully mix with the ionic liquid while not interacting with the Li ions to preserve the ionic liquid character, which is beneficial for Li-metal electrode stability. We report on the influence of a hydrofluoroether (HFE) diluent on ion dynamics and nanostructure of an ionic liquid electrolyte. We show that the ionic liquid and the diluent are fully miscible and that the solvation structure of the Li ions is not affected by the presence of HFE. The increase in the conductivity by the addition of the diluent is directly related to a decrease in viscosity with faster dynamics of all ionic species. However, the relative increase in mobility is considerably larger for the ionic liquid cation as a result of a preferred interaction with HFE. On the microscopic scale, more complex local non-Gaussian diffusive dynamics are found, faster than what is expected from the self-diffusion coefficient. The relative change of the dynamics with the addition of HFE on macro- and microscopic length scales correlates well, which underlines the connection between the motions probed on different length and time scales.
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| 4. |
- Lundin, Filippa, 1992
(författare)
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Local Structure and Dynamics of Next Generation Electrolytes - linking microscopic and macroscopic properties
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The electrolyte is a crucial part of a battery in terms of performance, longevity and safety. However, the state-of-the-art electrolytes for lithium-ion batteries are based on organic solvents and Li-salts (typically at 1M concentration) which are volatile and degrade at higher temperatures. In addition, these electrolytes are not suitable for next generation battery concepts where the use of metallic lithium at the anode side is a prerequisite. Thus, there is currently a strong effort to find new electrolyte concepts to both improve safety of current battery technology and pave way for next generation batteries. In the search for new electrolytes, highly concentrated electrolytes and ionic liquids have been proposed as alternatives through properties such as high thermal stability, lower reactivity with cell components and increased electrochemical stability window. A common feature for highly concentrated electrolytes and ionic liquids is an ordering on mesoscopic length scales, normally not found in simple liquids, resulting from the correlation between the ions. This nanostructure can be expected to influence the ion transport and a key to developing these new electrolyte concepts is to understand the structure and dynamics on mesoscopic length scales and how this links to macroscopic transport. In this thesis, the microscopic properties of ionic liquids and diluted ionic liquids are investigated together with highly concentrated electrolytes based on an organic solvent. To achieve this goal X-ray and neutron scattering are invaluable tools as they allow for measurements at the time and length scale of typical molecular motions and interactions. Complementary techniques such as conductivity and viscosity measurements, differential scanning calorimetry, and Raman spectroscopy have been used in order to link between the macroscopic and microscopic properties and between local structure and dynamics.
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| 5. |
- Lundin, Filippa, 1992, et al.
(författare)
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Pressure and Temperature Dependence of Local Structure and Dynamics in an Ionic Liquid
- 2021
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 125:10, s. 2719-2728
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Tidskriftsartikel (refereegranskat)abstract
- A detailed understanding of the local dynamics in ionic liquids remains an important aspect in the design of new ionic liquids as advanced functional fluids. Here, we use small-angle X-ray scattering and quasi-elastic neutron spectroscopy to investigate the local structure and dynamics in a model ionic liquid as a function of temperature and pressure, with a particular focus on state points (P,T) where the macroscopic dynamics, i.e., conductivity, is the same. Our results suggest that the initial step of ion transport is a confined diffusion process, on the nanosecond timescale, where the motion is restricted by a cage of nearest neighbors. This process is invariant considering timescale, geometry, and the participation ratio, at state points of constant conductivity, i.e., state points of isoconductivity. The connection to the nearest-neighbor structure is underlined by the invariance of the peak in the structure factor corresponding to nearest-neighbor correlations. At shorter timescales, picoseconds, two localized relaxation processes of the cation can be observed, which are not directly linked to ion transport. However, these processes also show invariance at isoconductivity. This points to that the overall energy landscape in ionic liquids responds in the same way to density changes and is mainly governed by the nearest-neighbor interactions.
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| 6. |
- Lundin, Filippa, 1992
(författare)
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Structure and Dynamics in Ionic Liquid and Highly Concentrated Electrolytes
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The electrolyte is a crucial part of a battery in terms of longevity and safety. However, the state-of-the-art electrolytes for lithium-ion batteries are based on organic solvents and Li-salts (typically 1M concentration) and are known to be volatile and to degrade at higher temperature. In the search for a safer electrolyte, highly concentrated electrolytes (HCEs) and ionic liquids (ILs) have been proposed as alternatives. The high salt concentration in HCEs (typically >4M) results in an increased electrochemical stability whereas ionic liquids, consisting only of ions, are known to have a negligible vapour pressure and high thermal stability. A common feature for HCEs and ILs is an ordering on mesoscopic length scales, normally not found in simple liquids, resulting from correlations between the ions. This nanostructure can be expected to influence the ion transport and a key to develop these new electrolyte concepts is to understand the structure and dynamics on the molecular level and how this links to macroscopic transport properties. The thesis focuses on the understanding of mesoscopic structure and dynamics in ILs and HCEs with the help of neutron and X-ray scattering with the aim to identify how local dynamical processes are influenced by the nanostrucutre. I have investigated an archetypal HCE system where the Li-salt LiTFSI is dissolved in acetonitrile and a model ionic liquid. Varying the Li-salt concentration in the HCE we can link the local processes to the development of the structure. The ion transport in the HCE takes place by the means of a jump diffusion and is highly dependent on the salt concentration and temperature of the system. For the ionic liquid we investigate the response of structure and dynamics to changes in both pressure and temperature with a particular focus on state points (P,T) where the macroscopic dynamics i.e. conductivity is constant. A conned diusion was found with a diusion coecient in agreement with macroscopic conductivity, thus providing a link between the microscopic and macroscopic dynamics.
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| 7. |
- Lundin, Filippa, 1992, et al.
(författare)
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Structure and dynamics of highly concentrated LiTFSI/acetonitrile electrolytes
- 2021
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 23:25, s. 13819-13826
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Tidskriftsartikel (refereegranskat)abstract
- High salt concentration has been shown to induce increased electrochemical stability in organic solvent-based electrolytes. Accompanying the change in bulk properties is a structural ordering on mesoscopic length scales and changes in the ion transport mechanism have also been suggested. Here we investigate the local structure and dynamics in highly concentrated acetonitrile electrolytes as a function of salt concentration. Already at low concentrations ordering on microscopic length scales in the electrolytes is revealed by small angle X-ray scattering, as a result of correlations of Li+ coordinating clusters. For higher salt concentrations a charge alternation-like ordering is found as anions start to take part in the solvation. Results from quasi-elastic neutron spectroscopy reveal a jump diffusion dynamical process with jump lengths virtually independent of both temperature and Li-salt concentration. The jump can be envisaged as dissociation of a solvent molecule or anion from a particular Li+ solvation structure. The residence time, 50-800 ps, between the jumps is found to be highly temperature and Li-salt concentration dependent, with shorter residence times for higher temperature and lower concentrations. The increased residence time at high Li-salt concentration can be attributed to changes in the interaction of the solvation shell as a larger fraction of TFSI anions take part in the solvation, forming more stable solvation shells.
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| 8. |
- Nitze, Florian, 1981, et al.
(författare)
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A binder-free sulfur/reduced graphene oxide aerogel as high performance electrode materials for lithium sulfur batteries
- 2016
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Societies' increasing need for energy storage makes it necessary to explore new concepts beyond the traditional lithium ion battery. A promising candidate is the lithium-sulfur technology with the potential to increase the energy density of the battery by a factor of 3-5. However, so far the many problems with the lithium-sulfur system have not been solved satisfactory. Here we report on a new approach utilizing a self-standing reduced graphene oxide based aerogel directly as electrodes, i.e. without further processing and without the addition of binder or conducting agents. We can thereby disrupt the common paradigm of "no battery without binder" and can pave the way to a lithium-sulfur battery with a high practical energy density. The aerogels are synthesized via a one-pot method and consist of more than 2/3 sulfur, contained inside a porous few-layered reduced graphene oxide matrix. By combining the graphene-based aerogel cathode with an electrolyte and a lithium metal anode, we demonstrate a lithium-sulfur cell with high areal capacity (more than 3 mAh/cm(2) after 75 cycles), excellent capacity retention over 200 cycles and good sulfur utilization. Based on this performance we estimate that the energy density of this concept-cell can significantly exceed the Department of Energy (DEO) 2020-target set for transport applications.
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| 9. |
- Rizell, Josef, 1996, et al.
(författare)
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Neutron Reflectometry Study of Solid Electrolyte Interphase Formation in Highly Concentrated Electrolytes
- 2023
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Ingår i: Small Structures. - : WILEY. - 2688-4062. ; 4:11
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Tidskriftsartikel (refereegranskat)abstract
- Highly concentrated electrolytes have been found to improve the cycle life and Coulombic efficiency of lithium metal anodes, as well as to suppress dendrite growth. However, the mechanism for these improvements is not well understood. Partly, this can be linked to the difficulty of accurately characterizing the solid electrolyte interphase (SEI), known to play an important role for anode stability and stripping/plating efficiency. Herein, in situ neutron reflectometry is used to obtain information about SEI formation in a highly concentrated ether-based electrolyte. With neutron reflectometry, the thickness, scattering length density (SLD), and roughness of the SEI layer formed on a Cu working electrode are nondestructively probed. The reflectivity data point to the formation of a thin (5 nm) SEI in the highly concentrated electrolyte (salt:solvent ratio 1:2.2), while a considerably thicker (13 nm) SEI is formed in an electrolyte at lower salt concentration (salt:solvent ratio 1:13.7). Further, the SEI formed in the electrolyte with high salt concentration has a higher SLD, suggesting that the chemical composition of the SEI changes. The results from neutron reflectometry correlate well with the electrochemical data from SEI formation.
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