Next Article in Journal
Synthesis, Characterization and Biological Activity of Hydrazones and Their Copper(II) Complexes
Previous Article in Journal
Transition Metal-Catalyzed, “Ligand Free” P–C Coupling Reactions under MW Conditions
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Proceeding Paper

Ionogels: Polimeric and Sol-Gel Silica Nanoscaffolds of Ionic Liquids as Smart Materials †

1
NaFoMAT Research Group, Departments of Applied Physics and Particle Physics, Faculty of Physics, Campus Vida, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain
2
Mesturas Research Group, Department of Physics and Earth Sciences, University of A Coruña, 15071 A Coruña, Spain
*
Authors to whom correspondence should be addressed.
Presented at the 26th International Electronic Conference on Synthetic Organic Chemistry, 15–30 November 2022; Available online: https://sciforum.net/event/ecsoc-26.
Chem. Proc. 2022, 12(1), 70; https://doi.org/10.3390/ecsoc-26-13686
Published: 17 November 2022

Abstract

:
The purpose of this work is to check the viability of mixtures of ionic liquids and lithium salt as electrolytes in Li- batteries. Firstly, the determination of the thermo-electrical properties of liquid mixtures of the ionic liquid N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide [BMPyrr][TFSI] with [Li][TFSI] salt at different concentrations was performed. Additionally, these results were compared with the corresponding ionogels of these mixtures designed by two different gelation methods, one of them using Poly (vinylidene fluoride) (PVDF) as a supporting matrix and the other one using a silica matrix.

1. Introduction

The energy transition towards forms of production and storage that allow complete sustainability and decarbonisation of the economic cycle is, at once, an urgent requirement of the current climate situation. The unstoppable energy transition process towards an increasingly sustainable and climate-neutral model based on renewable energies is related to the efficient storage and sustainable consumption of this energy. This is a huge worldwide challenge involving the scientific community, politicians and all of society [1].
Regarding efficient energy storage, as a result of the development of 4th and 5th generation recyclable batteries, new materials are one of the critical topics in current studies, especially for electrolyte and electrode designs [2]. In recent years, research related to new electrochemical materials has experienced great progress. Some of the most promising materials are ionic liquids (ILs), which are organic salts formed by a cation and an anion whose melting point is below 100 °C. The tuneability of the properties of ILs from the infinitely combinable anions and cations, and the possibility of introducing functional groups in their alkyl chains, make these fluids appropriate for many industrial applications, for example, electrolytes in mixtures of ILs and inorganic salts, mainly lithium salts [3,4].
ILs confinement in a matrix improves handling while reducing the possibility of spillage and the resulting grave consequences. This immobilization of ILs (or mixtures with inorganic salts) is known as gelation, and the resulting material is denominated as ionogel or ionic gels.
In this work, a pure IL (1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide) in liquid and gel state, obtained by two different routes, is analysed as a functional battery electrolyte in terms of broad band dielectric spectroscopy (BBDS). The effect of lithium salt addition to liquid and gel samples was also studied in terms of ionic conductivity.

2. Materials and Methods

2.1. Chemicals

For performing this work, an IL and a lithium salt with common anion, in liquid and gel form were selected. Table 1 shows a short description of the compounds used, molecular mass, short name, CAS identification number and provenance.

2.2. Gel Preparation

The first method is based on a solution of TMOS and DMDMS, which, in the presence of formic acid (FA), hydrolyses Si-O bonds, forming a 3D network in whose pores the IL is immobilized. This gelation method was based on the route devised by Brachet et al. [5], which can be summarized in three steps:
  • Firstly, TMOS and DMDMS with a molar rate 0.65 to 0.35 are mixed and stirred for 10 min.
  • Secondly, [BMPyrr][TFSI] at a 0.8 molar rate is added to the previous mixture and stirred for an additional 10 min.
  • Lastly, formic acid in a molar proportion of 3.3 is added, left in agitation for 2 min and finally, introduced in a Teflon mold.
The gel must remain covered for 2 days, and then left uncovered for another 5 days to achieve an accurate gelation. The gel may contain some impurities (precursors rest and other volatile products formed during the gelation), so a purifier vacuum process must be performed.
The second gelation method is based on PVDF, which is a nanometric powder that is mixed with dimethylformamide (DMF), whose only purpose is to triggers the gelation reaction [6]. The process followed to obtain the precursor matrix is:
  • Mix 8% PVDF in mass with 92% DMF and stir for 3 h.
  • Next, considering that PVDF is the hosting matrix (and DMF is only a solute to trigger the gelation process), the mass of PVDF vs IL is adjusted again, in mass proportions of 13% of PVDF and 87% of IL, and then mixed for 3 min and kept in a Teflon mold.
The gel must remain covered for 2 days and then remain open to the environment for another 5 days until the major part of the DMF has evaporated. To finish the gelation process, the gel is placed in a vacuum for 1 h, and then after, a heat treatment is performed, which consists of keeping the gel in a vacuum at 110 °C for 40 min. When the heat treatment is completed, the gel must be kept in a vacuum for a minimum of 24 h to evaporate the impurities produced by the gelation process.

2.3. Experimental Procedure

The electrical properties of the pure IL and mixtures were analyzed through complex impedance spectroscopy in a frequency range of 20 Hz to 1 MHz and a temperature interval of 273–323 K by using a RLC HP 4284A precision meter from Agilent, working with 8610 selectable frequencies between the selected frequency range. The basic accuracy of HP 4284 A is better than 0.05%. The applied sinusoidal voltage presents an amplitude of 0.2 V. This RLC precision meter presents 20 impedance parameters, each one with its own measurement range, i.e., G and B (conductance and susceptance, respectively), with a measurable range between 0.01 nS to 99.9999 S, while for Z’ and Z’’ (resistance and reactance, respectively), the measurable range is between 0.01 mΩ to 99.9999 Ω.
A Swagelok coin cell with two parallel electrodes of stainless steel (4 mm radius and 1 mm of thickness) was used for experimental measurements. The short circuit compensation of the cell and its correction coefficient were considered to eliminate the effect of stray capacitance during the evaluation of the frequency-dependent values of complex dielectric function [7].
A calibrated Julabo F25 thermostat was used to control the temperature of the sample; the uncertainty of the temperature was lower than 0.1 K. All of the measurements were performed using an isothermal regime.

3. Results

The real dielectric constant ( ε ) spectra (Figure 1) differs in two characteristic regions in the studied frequency range, separated by a frequency around 2 kHz. At the low frequency range, ε decreases linearly over five orders of magnitude, with a slope greater than the unity as the frequency increases. The great response of ε at low frequencies is due to the electrode polarization contribution (EP). This effect represents the formation of the double electric layer (EDL) at the interface of the dielectric material and the electrode, due to the accumulation of ions and free charges [8].
When the frequency increases, the dipole rotational contribution becomes greater and ε follows the Maxwell Boltzmann statistics [9]. As the frequency increases, the dielectric response decreases due to the difficulty of the ions to follow the electromagnetic vibrations. At a fixed frequency, the ε response enlarges as the temperature increases, which reveals that the concentration of the induced ions contributing to the formation of the EDL becomes greater with increasing temperature [10].
Regarding the imaginary part of the dielectric constant ( ε ) , it shows a plateau-like measurement at low frequencies with a maximum that increases with temperature, followed by a linear decrement in a double-logarithmic scale. The decrement slope is approximately −1.00, which is characteristic of the ohmic region (the current density has a linear response with the applied electric field) [11]. The ohmic region varies as the temperature increases, since the initial frequency moves to greater frequencies. The plateau at low frequencies is caused by non-aligned lines of the ions and the applied electric field [12].
When the temperature is over 40 °C, the ohmic region of pure [BMPyrr][TFSI] is outside of the studied region, so it is not possible to obtain the ionic conductivity by the applied method, making it necessary to enlarge the frequency range to over 1 MHz.
Every compound shows an increasing conductivity as temperature increases (Figure 2). When temperature rises, the viscosity of the compound becomes lower; thus, the ions can flow easily giving greater transport properties.
The salt addition triggers a decrease in ionic conductivity due to a reduction in fluidity (increase of viscosity with salt addition). The decrease in conductivity is due to the increasing formation of L i ( T F S I ) 2 as a result of the Li ions coordinating with T F S I anions [13].
The gelation provokes a diminished conductivity at every temperature and salt concentration. The decrease in ionic conductivity is caused not only by ion concentration reduction in gelation, but also by the mobility decrease that could be due to the nanoconfinement in the matrix scaffold (Figure 2).
The silica gel ionic conductivity is lower than PVDF gel, becoming half at 50 °C (Table 2). This is because on silica gels, the IL proportion is much lower than PVDF gels (0.8 molar rate in silica gels, 83% mass in PVDF gels), which reduces the ions’ proportion and conductivity.
Both liquid and gel PVDF and silica samples follow a VFT behavior [14], which suggests that in both states, the dynamic structure is similar and the energy process of conduction does not vary substantially (Figure 2).

4. Conclusions

The impedance and dielectric properties of a solution phase and gel of [BMPyrr][TFSI] were studied in this work, as well as the effect of salt addition.
  • The mobility of ions becomes greater when the temperature increases.
  • An enhancement of ionic conductivity is observed with an increase of temperature, which could be justified by a reduction of viscosity.
  • Conductivity decreases with the addition of salt due to an increase of viscosity, and also decreases with the nanoconfinement of the IL in the matrix scaffolds, probably due to electrostatic interactions between IL and the nano-scaffold.

Author Contributions

Conceptualization, L.M.V., J.S. and J.J.P.; methodology, A.S., P.V. software, A.S. and P.V.; validation, A.S., P.V., J.J.P., M.V., Ó.C., L.M.V. and J.S.; data curation, A.S., P.V. and J.J.P.; writing—original draft preparation, A.S., P.V., J.J.P. and J.S.; writing—review and editing, A.S., P.V., J.J.P., M.V., Ó.C., L.M.V. and J.S.; supervision, J.J.P., M.V. and J.S.; project administration, Ó.C. and L.M.V.; funding acquisition, A.S., P.V., J.J.P., M.V., Ó.C., L.M.V. and J.S. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by Spanish Ministry of Economy and Competitiveness and FEDER Program through the project MAT2017-89239-C2-1-P and the Network Ionic Systems for energy sustainability (SISE) RED2018-102679-T and by Xunta de Galicia through GRC ED431C 2020/10 project and the Galician Network of Ionic Liquids (ReGaLIs) ED431D 2017/06.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

P. Vallet and J. J. Parajó thank funding support of FPI Program from 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

  1. Arbabzadeh, M.; Sioshansi, R.; Johnson, J.X.; Keoleian, G.A. The Role of Energy Storage in Deep Decarbonization of Electricity Production. Nat. Commun. 2019, 10, 3413. [Google Scholar] [CrossRef] [PubMed]
  2. Menne, S.; Pires, J.; Anouti, M.; Balducci, A. Protic Ionic Liquids as Electrolytes for Lithium-Ion Batteries. Electrochem. Commun. 2013, 31, 39–41. [Google Scholar] [CrossRef]
  3. Liew, C.W.; Ramesh, S.; Ramesh, K.; Arof, A.K. Preparation and Characterization of Lithium Ion Conducting Ionic Liquid-Based Biodegradable Corn Starch Polymer Electrolytes. J. Solid State Electrochem. 2012, 16, 1869–1875. [Google Scholar] [CrossRef]
  4. Russina, O.; Caminiti, R.; Méndez-Morales, T.; Carrete, J.; Cabeza, O.; Gallego, L.J.; Varela, L.M.; Triolo, A. How Does Lithium Nitrate Dissolve in a Protic Ionic Liquid? J. Mol. Liq. 2015, 205, 16–21. [Google Scholar] [CrossRef]
  5. Brachet, M.; Gaboriau, D.; Gentile, P.; Fantini, S.; Bidan, G.; Sadki, S.; Brousse, T.; le Bideau, J. Solder-Reflow Resistant Solid-State Micro-Supercapacitors Based on Ionogels. J. Mater. Chem. A Mater. 2016, 4, 11835–11843. [Google Scholar] [CrossRef]
  6. le Bideau, J.; Viau, L.; Vioux, A. Ionogels, Ionic Liquid Based Hybrid Materials. Chem. Soc. Rev. 2011, 40, 907–925. [Google Scholar] [CrossRef] [PubMed]
  7. Mehrotra, S.; Kumbharkhane, A.; Chaudhari, A. Theoretical and Experimental Aspects of Time Domain Permittivity Spectroscopy. In Binary Polar Liquids; Elsevier: Amsterdam, The Netherlands, 2017; pp. 1–43. [Google Scholar]
  8. Vadhva, P.; Hu, J.; Johnson, M.J.; Stocker, R.; Braglia, M.; Brett, D.J.L.; Rettie, A.J.E. Electrochemical Impedance Spectroscopy for All-Solid-State Batteries: Theory, Methods and Future Outlook. ChemElectroChem 2021, 8, 1930–1947. [Google Scholar]
  9. Rana, V.A.; Barot, D.K.; Vankar, H.P.; Pandit, T.R.; Karakthala, J.B. AC/DC Conductivity and Dielectric Relaxation Behavior of Ionic Solutions of 1-Butyl-3-Methylimidazolium Chloride in Methanol. J. Mol. Liq. 2019, 296, 111804. [Google Scholar] [CrossRef]
  10. Kremer, F.; Schönhals, A. (Eds.) Broadband Dielectric Spectroscopy; Springer Berlin Heidelberg: Berlin/Heidelberg, Germany, 2003; ISBN 978-3-642-62809-2. [Google Scholar]
  11. Vallet, P.; Bouzón-Capelo, S.; Méndez-Morales, T.; Gómez-González, V.; Arosa, Y.; de la Fuente, R.; López-Lago, E.; Rodríguez, J.R.; Gallego, L.J.; Parajó, J.J.; et al. On the Physical Properties of Mixtures of Nitrate Salts and Protic Ionic Liquids. J. Mol. Liq. 2022, 350, 118483. [Google Scholar] [CrossRef]
  12. Tu, W.; Richert, R.; Adrjanowicz, K. Dynamics of Pyrrolidinium-Based Ionic Liquids under Confinement. I. Analysis of Dielectric Permittivity. J. Phys. Chem. C 2020, 124, 5389–5394. [Google Scholar] [CrossRef]
  13. Kim, J.-K.; Lim, D.-H.; Scheers, J.; Pitawala, J.; Wilken, S.; Johansson, P.; Ahn, J.-H.; Matic, A.; Jacobsson, P. Properties of N-Butyl-N-Methyl-Pyrrolidinium Bis(Trifluoromethanesulfonyl) Imide Based Electrolytes as a Function of Lithium Bis(Trifluoromethanesulfonyl) Imide Doping. J. Korean Electrochem. Soc. 2011, 14, 92–97. [Google Scholar] [CrossRef]
  14. Noor, S.A.M.; Bayley, P.M.; Forsyth, M.; MacFarlane, D.R. Ionogels Based on Ionic Liquids as Potential Highly Conductive Solid State Electrolytes. Electrochim. Acta 2013, 91, 219–226. [Google Scholar] [CrossRef]
Figure 1. Real and Imaginary dielectric constant against frequency. (a) Pure [BMPyrr][TFSI]; (b)[BMPyrr][TFSI] PVDF gel. (c) [BMPyrr][TFSI] silica gel.
Figure 1. Real and Imaginary dielectric constant against frequency. (a) Pure [BMPyrr][TFSI]; (b)[BMPyrr][TFSI] PVDF gel. (c) [BMPyrr][TFSI] silica gel.
Chemproc 12 00070 g001
Figure 2. Ionic conductivity against temperature.
Figure 2. Ionic conductivity against temperature.
Chemproc 12 00070 g002
Table 1. Identification of chemicals used in this work.
Table 1. Identification of chemicals used in this work.
NameMolecular Mass (g∙mol−1)Short NameCAS NumberPurity Supplier
Ionic liquid: 1-butyl-1methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide422.41[BMPyrr][TFSI]223437-11-4>99%
IoLiTec
Salt: Lithium bis(trifluoromethanesulfonyl)imide287.09[Li][TFSI]90076-65-6>99%
Sigma Aldrich
Gel Precursor: Poly(vinylidene fluoride)Mw ∼ 534,000PVDF24937-79-9Alfa Aesar
Gel Precursor: Tetramethyl orthosilicate152.22TMOS681-84-598%
Sigma Aldrich
Gel Precursor: Dimethoxydimethylsilane120.22DMDMS1112-39-698%
Sigma Aldrich
Table 2. Compound ionic conductivity at different temperatures.
Table 2. Compound ionic conductivity at different temperatures.
T [°C]Pure IL0.1 mPure PVDF 0.1 m PVDFPure Silica 0.1 m Silica
00.0735(90)0.0642(63)0.0546(51)0.0495(59)0.0240(22)0.0388(37)
100.0119(90)0.106(13)0.096(13)0.086(13)0.0425(51)0.0473(53)
200.207(51)0.183(36)0.162(26)0.139(32)0.076(12)0.071(11)
250.266(73)0.233(51)0.192(43)0.186(47)0.087(16)0.092(16)
40 0.39(11)0.355(99)0.279(81)0.137(39)0.153(34)
50 0.65(12)0.49(11)0.397(95)0.211(54)0.199(52)
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Santiago, A.; Vallet, P.; Parajó, J.J.; Villanueva, M.; Cabeza, Ó.; Varela, L.M.; Salgado, J. Ionogels: Polimeric and Sol-Gel Silica Nanoscaffolds of Ionic Liquids as Smart Materials. Chem. Proc. 2022, 12, 70. https://doi.org/10.3390/ecsoc-26-13686

AMA Style

Santiago A, Vallet P, Parajó JJ, Villanueva M, Cabeza Ó, Varela LM, Salgado J. Ionogels: Polimeric and Sol-Gel Silica Nanoscaffolds of Ionic Liquids as Smart Materials. Chemistry Proceedings. 2022; 12(1):70. https://doi.org/10.3390/ecsoc-26-13686

Chicago/Turabian Style

Santiago, Antía, Pablo Vallet, Juan José Parajó, María Villanueva, Óscar Cabeza, Luis Miguel Varela, and Josefa Salgado. 2022. "Ionogels: Polimeric and Sol-Gel Silica Nanoscaffolds of Ionic Liquids as Smart Materials" Chemistry Proceedings 12, no. 1: 70. https://doi.org/10.3390/ecsoc-26-13686

Article Metrics

Back to TopTop