Structural Characterization by NMR Procedure of C4C1Pyrr TFSI Doped with Lithium TFSI Salt in Liquid and Gel States †
by
, ,
Pablo Vallet
1,*, 
Juan José Parajó
1,2,
Lois Fernández-Míguez
1,
Félix Sotuela
1,
Ángel Morcillo
1,
María Villanueva
1,
Óscar Cabeza
3,
Vladimir V. Matveev
4,
Alexandr V. Ievlev
4,
Konstantin Tutukin
4,
Luis Miguel Varela
1 and
Josefa Salgado
1 1
NAFOMAT Group, Departamentos de Física Aplicada y Física de Partículas, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain
2
Departamento de Química e Bioquímica, CIQUP-Centro de Investigaçao em Química da Universidade do Porto, Universidade do Porto, P-4169-007 Porto, Portugal
3
MESTURAS Group, Departamento de Física y Ciencias de la Tierra, Universidade da Coruña, 15071 A Coruña, Spain
4
Department of Nuclear Physics Research Methods, Saint Petersburg State University, 7/9 Universitetskaya nab., 199034 Saint Petersburg, Russia
*
Author to whom correspondence should be addressed.
†
Presented at the 24th International Electronic Conference on Synthetic Organic Chemistry, 15 November–15 December 2020; Available online: https://ecsoc-24.sciforum.net/.
Chem. Proc. 2021, 3(1), 115; https://doi.org/10.3390/ecsoc-24-08370
Published: 14 November 2020
(This article belongs to the Proceedings of The 24th International Electronic Conference on Synthetic Organic Chemistry)
Abstract
:Ionic liquids represent a viable option as electrolytes for electrochemical applications such as energy storage devices, due to their high ionic conductivity and wide electrochemical window. However, liquid electrolytes present important problems of safety and performance, and encapsulation in a solid matrix can be a good solution to improve it. In this work, changes in the structure of the mixtures of ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide against the concentration of the salt (0, 0.1, and 1.5 molal), and the effect of nanoconfinement through gelation process were studied using NMR technique.
1. Introduction
The future has as a challenge to achieve decarbonization, both in industry and of the economy, for a green and sustainable future. One of the main options is an ecological transition where fossil fuels are replaced by renewable ways of obtaining energy without carbon emissions into the atmosphere. This ecological transition brings new scientific and technical challenges such as the development and improvement of energy storage systems.
The current situation of electrolyte manufacturing is based on flammable and volatile mixtures that can put the operator’s safety at risk when handling and assembling these into a commercial battery. This situation allows ionic liquids (ILs) and their mixtures with inorganics salts to be considered as a good alternative to replace the commercial electrolytes, due to their remarkable properties for electrochemical applications [1,2,3].
One of the main problems of common electrolytes, ILs among them, when handling and assembling in batteries, is their liquid condition, which complicates their manufacture when it comes to large-scale implementation. In the case of ILs, a solution could be the nanoconfinement of the ionic liquid in an organic matrix through sol–gel method [4] in order to keep its main properties intact obtaining a quasi-solid like material [5].
In this work, an NMR study was carried out with the main purpose to structurally analyze, with the salt addition and the effect of the gelling process, on the IL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide C4C1Pyrr TFSI and lithium bis(trifluoromethylsulfonyl)imide (Li TFSI) against the concentration of the salt (0, 0.1 and 1.5 molal).
2. Materials and Methods
2.1. Chemicals
Three different mixtures of the ionic liquid C4C1Pyrr TFSI with the salt Li TFSI salt were prepared via stirring procedure (pure IL, 0.1 mol Kg−1 and 1.5 mol Kg−1), being 1.5 mol kg−1 the saturated one.
In Table 1, a brief description of the chemical compounds used in this work can be found, where the molecular weight, structure, CAS number, supplier, and purity is indicated.
2.2. Gelation Procedure
The sol-gel process for synthesizing the gel samples was an adaptation of the methodology reported by [6], which was carried out under acidic conditions. A brief description of the used method to gelling samples using volumetric proportions is:
A mixture of 2:1 volumetric parts of Formic Acid (FA):TEOS were stirred for 18 min at 40 °C in a flask. After this time, 4 volumetric parts of IL + lithium salt at desired concentration were added and stirred for 45 s more.
Finally, the pre-gel sample was deposited in a vial and stored at a room temperature for 24/48 h until full gelation. Once gelation is complete samples were submitted to high vacuum for 24 h.
3. Experimental Procedure
NMR sample were placed in 5 mm diameter tubes. A spectrometer Bruker DRX500 de 11.74 T (500 MHz resonance of 1H) were used to analyze both gel and liquid samples at 313.15 K, equipped by:
- Reverse detection probe 1H/13C/15N (standard tube 5 mm) with Z gradient.
- 1H/X multinuclear reverse detection probe (standard tube 5 mm) with Z gradient.
- X/1H multinuclear probe for 10 mm diameter tube.
- BACSTM 50-sample robot sample changer.
- Two waveform generators for selective pulses.
- Liquid N2 cooling device for low temperature experiments.
- Top Spin control software v. 1.3 under Linux Red-Hat Enterprise 5.1 Operating System.
4. Results
Figure 1 shows 1H spectra for the C4C1Pyrr TFSI + Li TFSI mixtures in liquid and gel forms. The relative position of CH3 corresponding to the butyl chain of the IL has been adjusted to the value provided by Pavel et al. [7]. Regarding multiplet information of the different present peaks, the resolution reached was not enough to determine with exactitude what kind of splitting is present. Peak shift was indicated in ppm and can be found in Table 2. As can be seen, both the salt addition and the gelation procedure keep the peak position at a similar value (shift) compared to the pure sample; this indicates that the structure remains constant without a significant change in the structural arrangement. The most remarkable result, in both 1H and 13C (Figure 2) spectra, is the apparition of new peaks due to the impurities during the gelation procedure on the saturation concentration. These impurities were impossible to extract during the annealing or vacuum.
As it can be seen in Table 3, nanoencapsulation of the IL translates in a widening of the FWHM (full width at half maximum) both 1H and 13C spectrum, this is due to a slight slowdown in molecular dynamics of the ionic liquid [8], but this widening is not enough to consider it as a solid, so the nanoencapsulated IL keeps its properties as liquid-like, inside the organic matrix.
5. Conclusions
This work reports 1H and 13C NMR spectra for mixtures of an IL, C4C1Pyrr TFSI and its mixture with Li TFSI and their gelation via sol-gel process. Slight differences have been found except for saturated mixture on gel sample, which shows impurities versus the rest of samples, liquid and gel.
The most remarkable result is that nanoencapsulated IL keeps its properties as liquid-like, inside the organic matrix.
Author Contributions
Conceptualization, P.V., J.S., V.V.M., and L.M.V.; methodology and data, P.V., J.J.P., L.F.-M., F.S., Á.M., A.V.I., and K.T.; software, P.V., L.F.-M., V.V.M., A.V.I., K.T., and L.M.V. writing—original draft preparation, P.V., J.J.P., J.S., M.V., V.V.M.; Ó.C., and L.M.V.; funding acquisition, L.M.V., Ó.C., J.S., and M.V. All authors have read and agreed to the published version of the manuscript.
Funding
This work was supported by the Spanish Ministry of Economy and Competitiveness and FEDER Program through the projects MAT2014-57943-C3-1-P, MAT2014-57943-C3-3-P, MAT2017-89239-C2-1-P as well as by Xunta de Galicia through GRC ED431C 2020/10 project and the Galician Network of Ionic Liquids (ReGaLIs) ED431D 2017/06. P. Vallet and J. J. Parajó thank funding support of FPI Program from the Spanish Ministry of Science, Education and Universities and I2C postdoctoral Program of Xunta de Galicia, respectively.
Conflicts of Interest
The authors declare no conflict of interest.
References
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Figure 1.
The 1H spectra of analyzed samples. Inset shows C4C1Pyrr cation with the corresponding numbered atomic bonds. The Y-axis is measured in arbitrary units (AU).
Figure 1.
The 1H spectra of analyzed samples. Inset shows C4C1Pyrr cation with the corresponding numbered atomic bonds. The Y-axis is measured in arbitrary units (AU).
Figure 2.
The 13C spectra of analyzed samples. Inset shows C4C1Pyrr cation with the corresponding numbered atomic bonds. The Y-axis is measured in arbitrary units (AU).
Figure 2.
The 13C spectra of analyzed samples. Inset shows C4C1Pyrr cation with the corresponding numbered atomic bonds. The Y-axis is measured in arbitrary units (AU).
Table 1.
Chemicals.
| Name | Molecular Weight (g mol−1) | Structure | Abbreviation CAS Number | Provenance Purity |
|---|---|---|---|---|
| 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide | 422.41 |  | C4C1Pyrr TFSI 223437-11-4 | Iolitec >0.99 |
| Lithium bis(trifluoromethylsulfonyl)imide | 287.09 |  | Li TFSI 90076-65-6 | Acros Organics >0.99 |
| Tetraethoxysilane | 208.33 |  | TEOS 78-10-4 | Sigma Aldrich >0.98 |
Table 2.
Peak shift (in ppm) of liquid and gel mixtures for 1H and 13C spectrum.
| 1H Spectra | ||||||||
|---|---|---|---|---|---|---|---|---|
| Sample | 10 | 9 | 8 | 1, 2 | 6 | 7 | 3, 5 | |
| Pure IL (liquid) | 0.93 | 1.35 | 1.72 | 2.16 | 2.97 | 3.27 | 3.45 | |
| IL+Li TFSI 0.1m (liquid) | 0.93 | 1.34 | 1.72 | 2.16 | 2.97 | 3.27 | 3.45 | |
| IL+Li TFSI 1.5m (liquid) | 0.93 | 1.36 | 1.71 | 2.17 | 2.95 | 3.24 | 3.42 | |
| Pure IL (gel) | 0.93 | 1.35 | 1.72 | 2.16 | 2.97 | 3.28 | 3.46 | |
| IL+Li TFSI 0.1m (gel) | 0.93 | 1.35 | 1.72 | 2.16 | 2.97 | 3.28 | 3.45 | |
| IL+Li TFSI 1.5m (gel) | 0.93 | 1.36 | 1.73 | 2.18 | 2.98 | 3.27 | 3.45 | |
| 13C Spectra | ||||||||
| Sample | 10 | 9 | 1,2 | 8 | 3, 5 | 7 | 6 | CF3 |
| Pure IL (liquid) | 13.40 | 19.99 | 21.92 | 26.03 | 48.59 | 64.90 | 64.95 | 120.73 (Q) |
| IL+Li TFSI 0.1m (liquid) | 13.40 | 20.00 | 21.93 | 26.04 | 48.62 | 64.93 | 64.98 | 120.70 (Q) |
| IL+Li TFSI 1.5m (liquid) | 13.40 | 20.10 | 22.04 | 26.21 | 48.93 | 65.28 | 65.38 | 120.47 (Q) |
| Pure IL (gel) | 13.40 | 19.98 | 21.88 | 26.03 | 48.52 | 64.87 | UNDEF | 120.68 (Q) |
| IL+Li TFSI 0.1m (gel) | 13.40 | 19.97 | 21.89 | 26.02 | 48.55 | 64.90 | UNDEF | 120.68 (Q) |
| IL+Li TFSI 1.5m (gel) | 13.40 | 20.03 | 21.99 | 26.14 | 48.75 | 65.14 | UNDEF | 120.51 (Q) |
Table 3.
FWHM (in Hz) of liquid and gel mixtures for 1H and 13C spectrum.
| 1H Spectra | ||||||||
|---|---|---|---|---|---|---|---|---|
| Sample | 10 | 9 | 8 | 1, 2 | 6 | 7 | 3, 5 | |
| Pure IL (liquid) | 19.29 | 25.26 | 28.19 | 20.49 | 12.49 | 25.37 | 22.59 | |
| IL+Li TFSI 0.1m (liquid) | 13.89 | 21.06 | 23.67 | 15.56 | 6.64 | 19.92 | 16.55 | |
| IL+Li TFSI 1.5m (liquid) | 24.66 | 32.62 | 35.26 | 24.86 | 15.81 | 31.94 | 32.72 | |
| Pure IL (gel) | 58.75 | 65.47 | 68.43 | 62.56 | 42.89 | 58.75 | 72.13 | |
| IL+Li TFSI 0.1m (gel) | 87.65 | 100.87 | 99.37 | 99.43 | 88.85 | 105.36 | 106.75 | |
| IL+Li TFSI 1.5m (gel) | 80.54 | 84.10 | 79.83 | 104.22 | 72.43 | 108.05 | 100.13 | |
| 13C Spectra | ||||||||
| Sample | 10 | 9 | 1,2 | 8 | 3,5 | 7 | 6 | CF3 |
| Pure IL (liquid) | 9.2 | 9.4 | 10.3 | 6.8 | 9.7 | 6.7 | 5.7 | 5.8; 5.4; 5.2; 5.2 |
| IL+Li TFSI 0.1m (liquid) | 5.5 | 5.7 | 6.7 | 4.3 | 9.1 | 5.3 | 6.2 | 3.9; 3.6; 3.5; 3.5 |
| IL+Li TFSI 1.5m (liquid) | 13.2 | 16.2 | 18.0 | 10.9 | 17.6 | 8.3 | 21.6 | 13.9; 9.4; 8.7; 11.6 |
| Pure IL (gel) | 23.7 | 30.8 | 31.2 | 33.4 | 28.8 | 40.3 | 21.3; 25.8; 25.6; 29.1 | |
| IL+Li TFSI 0.1m (gel) | 27.8 | 33.6 | 33.4 | 39.2 | 35.6 | 41.7 | 23.1; 25.3; 23.9; 25.5 | |
| IL+Li TFSI 1.5m (gel) | 21.9 | 24.1 | 23.1 | 24.3 | 27.0 | 30.8 | 24.8; 21.3; 23.6; 21.0 | |
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Vallet, P.; Parajó, J.J.; Fernández-Míguez, L.; Sotuela, F.; Morcillo, Á.; Villanueva, M.; Cabeza, Ó.; Matveev, V.V.; Ievlev, A.V.; Tutukin, K.; et al. Structural Characterization by NMR Procedure of C4C1Pyrr TFSI Doped with Lithium TFSI Salt in Liquid and Gel States. Chem. Proc. 2021, 3, 115. https://doi.org/10.3390/ecsoc-24-08370
AMA Style
Vallet P, Parajó JJ, Fernández-Míguez L, Sotuela F, Morcillo Á, Villanueva M, Cabeza Ó, Matveev VV, Ievlev AV, Tutukin K, et al. Structural Characterization by NMR Procedure of C4C1Pyrr TFSI Doped with Lithium TFSI Salt in Liquid and Gel States. Chemistry Proceedings. 2021; 3(1):115. https://doi.org/10.3390/ecsoc-24-08370
Chicago/Turabian StyleVallet, Pablo, Juan José Parajó, Lois Fernández-Míguez, Félix Sotuela, Ángel Morcillo, María Villanueva, Óscar Cabeza, Vladimir V. Matveev, Alexandr V. Ievlev, Konstantin Tutukin, and et al. 2021. "Structural Characterization by NMR Procedure of C4C1Pyrr TFSI Doped with Lithium TFSI Salt in Liquid and Gel States" Chemistry Proceedings 3, no. 1: 115. https://doi.org/10.3390/ecsoc-24-08370
