Preserving fast ion dynamics while introducing mechanical rigidity in gelatin-based ionogels

• Published in: Soft matter 2023-02, Vol.19 (7), p.1418-1428
• Main Authors: Pabst, Florian, Kraus, Jennifer, Reynolds, Matthew, Mattsson, Johan, Blochowicz, Thomas
• Format: Article
• Language: English
• Subjects: Batteries; Electrolyte leakage; Electrolytes; Electrolytic cells; Fuel cells; Fuel technology; Gelatin; Gels; Glass transition temperature; Ion currents; Ion dynamics; Ion transport; Ionic liquids; Ions; Light scattering; Mechanical analysis; Mixtures; Photon correlation spectroscopy; Photovoltaic cells; Photovoltaics; Rheological properties; Rheology; Rigidity; Room temperature; Spectroscopy
• ISSN: 1744-683X; 1744-6848
• DOI: 10.1039/d2sm01143c

Ionogels are gels containing ions, often an ionic liquid (IL), and a gelling agent. They are promising candidates for applications including batteries, photovoltaics or fuel cells due to their chemical stability and high ionic conductivity. In this work we report on a thermo-irreversible ionic gel prepared from a mixture of the ionic liquid 1-butyl-3-methylimidazolium ([BMIM]) dicyanamide ([DCA]), water and gelatin, which combines the advantages of an ionic liquid with the low cost of gelatin. We use (i) dielectric spectroscopy to monitor the ion transport, (ii) dynamic light scattering techniques to access the reorientational motions of the ions, as well as fluctuations of the gel matrix, and (iii) rheology to determine the shear response from above room temperature down to the glass transition. In this way, we are able to connect the microscopic ion dynamics with the meso- and macroscopic behavior of the gelatin matrix. We show, by comparing our results to those for a IL-water mixture from a previous study, that although some weak additional slow relaxation modes are present in the gel, the overall ion dynamics is hardly changed by the presence of gelatin. The macroscopic mechanical response, as probed by rheology, is however dominated by the gel matrix. This behaviour can be highly useful e.g. in battery gel electrolytes which prevent electrolyte leakage and combine mechanical rigidity and flexibility. Combining light scattering, dielectric spectroscopy and rheology on a gelatin-based ionogel, we demonstrate that microscopic ion transport and dynamics are unaffected by the gel matrix, even though the matrix dominates the mechanical response.