| 41. |
- Tsurumaki, Akiko, et al.
(author)
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Enhanced safety and galvanostatic performance of high voltage lithium batteries by using ionic liquids
- 2019
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In: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 316, s. 1-7
-
Journal article (peer-reviewed)abstract
- We demonstrate that the addition of 1-butyl-1-methylpyrrolidinium hexafluorophosphate ([Py-14]PF6) to 1.0 M LiPF6 in ethylene carbonate-dimethyl carbonate (LP30) widens the temperature range, in which the electrolyte mixtures are ion conductive and safe. Specifically, at the concentrations of [Py-14]PF6 above 50 wt%, the electrolyte mixtures exhibit a flash point higher than room temperature and fulfill the requirements of liquids having controlled flammability. In this concentration range, also crystallization of the mixtures is completely suppressed, and low temperature ionic conductivity is improved. With respect to the electrochemical properties at room temperature, electrochemical stability window is widened by the addition of [Py-14]PF6 to LP30. However, it comes at the cost of slightly increased overall impedance and overpotential in Li vertical bar Li symmetric cells. We utilize these mixed electrolytes in high voltage Li vertical bar LiNi0.5Mn1.5O4 cells. In the presence of 30 wt% and 50 wt% of [Py-14]PF6 in LP30, the cells exhibit high specific capacity of about 110 mAh g(-1) over 200 cycles and improved coulombic efficiency, suggesting [Py-14]PF6 is a promising additive for the electrolyte in high-voltage, stable and safe lithium batteries.
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| 42. |
- Verwohlt, Jan, et al.
(author)
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Low Dose X-Ray Speckle Visibility Spectroscopy Reveals Nanoscale Dynamics in Radiation Sensitive Ionic Liquids
- 2018
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In: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 120:16
-
Journal article (peer-reviewed)abstract
- X-ray radiation damage provides a serious bottleneck for investigating microsecond to second dynamics on nanometer length scales employing x-ray photon correlation spectroscopy. This limitation hinders the investigation of real time dynamics in most soft matter and biological materials which can tolerate only x-ray doses of kGy and below. Here, we show that this bottleneck can be overcome by low dose x-ray speckle visibility spectroscopy. Employing x-ray doses of 22-438 kGy and analyzing the sparse speckle pattern of count rates as low as 6.7×10-3 per pixel, we follow the slow nanoscale dynamics of an ionic liquid (IL) at the glass transition. At the prepeak of nanoscale order in the IL, we observe complex dynamics upon approaching the glass transition temperature TG with a freezing in of the alpha relaxation and a multitude of millisecond local relaxations existing well below TG. We identify this fast relaxation as being responsible for the increasing development of nanoscale order observed in ILs at temperatures below TG.
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| 43. |
- Xiong, Shizhao, 1985, et al.
(author)
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Role of organic solvent addition to ionic liquid electrolytes for lithium–sulphur batteries
- 2015
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In: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069.
-
Journal article (peer-reviewed)abstract
- We investigate the role of the addition of an organic solvent to an ionic liquid electrolyte for the performance of lithium–sulphur (Li–S) batteries. We find that with a mixed electrolyte, formed by adding 10 wt% 1,3-dioxolane (DIOX) to an ionic liquid, the capacity of a Li–S cell is more than doubled, the rate capability and the cycling performance considerably improved, compared to a cell utilizing a neat ionic liquid electrolyte. The improved performance can be correlated with an enhanced ion transport, evidenced by an increased ionic conductivity and higher limiting current density, directly related to a decrease in viscosity and glass transition temperature of the mixed electrolytes. We show that this in turn is linked to a change in the local environment of the Li-ions where the organic solvent is incorporated in the coordination shell. In addition we show that the mixed electrolytes have a considerably higher thermal stability, in particular a dramatically increased flash point, and improved low temperature properties with respect to a conventional organic solvent based electrolyte currently used for Li–S batteries.
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| 44. |
- Yaghini, Negin, 1976, et al.
(author)
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Achieving enhanced ionic mobility in nanoporous silica by controlled surface interactions
- 2017
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In: Physical Chemistry Chemical Physics. - 1463-9084 .- 1463-9076. ; 19:8, s. 5727-5736
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Journal article (peer-reviewed)abstract
- We report a strategy to enhance the ionic mobility in an emerging class of gels, based on robust nanoporous silica micro-particles, by chemical functionalization of the silica surface. Two very different ionic liquids are used to fill the nano-pores of silica at varying pore filling factors, namely one aprotic imidazolium based (1-methyl-3-hexylimidazolium bis(trifluoromethanesulfonyl)imide, C6C1ImTFSI), and one protic ammonium based (diethylmethylammonium methanesulfonate, DEMAOMs) ionic liquid. Both these ionic liquids display higher ionic mobility when confined in functionalized silica as compared to untreated silica nano-pores, an improvement that is more pronounced at low pore filling factors (i.e. in the nano-sized pore domains) and observed in the whole temperature window investigated (i.e. from −10 to 140 °C). Solid-state NMR, diffusion NMR and dielectric spectroscopy concomitantly demonstrate this effect. The origin of this enhancement is explained in terms of weaker intermolecular interactions and a consequent flipped-ion effect at the silica interface strongly supported by 2D solid-state NMR experiments. The possibility to significantly enhance the ionic mobility by controlling the nature of surface interactions is extremely important in the field of materials science and highlights these structurally tunable gels as promising solid-like electrolytes for use in energy relevant devices. These include, but are not limited to, Li-ion batteries and proton exchange membrane (PEM) fuel cells.
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| 45. |
- Yaghini, Negin, 1976, et al.
(author)
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Effect of Water on the Local Structure and Phase Behavior of Imidazolium-Based Protic Ionic Liquids
- 2015
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 119:4, s. 1611-1622
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Journal article (peer-reviewed)abstract
- We report on the effect of water on local structure and phase behavior of two protic ionic liquids, C(2)HImTFSI and C(2)HImTfO. Raman and infrared spectroscopy are employed to investigate the local coordination state. We find that water interacts weakly with TFSI- while more specifically with TfO- through the - SO3 group. Additionally, we observe that upon addition of water the - NH stretching frequency does not change in C(2)HImTFSI, while it red-shifts in C(2)HImTfO, indicative of different hydrogen bonding configurations. Supported by the appearance of some additional features in the 800-1000 cm(-1) frequency range where ring out-of-plane bending (?) modes are found, we hypothesize that in C(2)HImTFSI water interacts only with the cation coordinating to the ring C2H and the N3H sites, while it interacts with both cation and anion in C(2)HImTfO forming hydrogen bonds that involve the cationic N-H site as well as the anionic - SO3 group. These different local structures also reflect in the phase behavior investigated by DSC, which reveals a more homogeneous solution when water is added to C(2)HImTfO, as compared to H2O/C(2)HImTFSI mixtures. Finally we report that the addition of water also significantly affects both T-m and T-g.
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