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Combining NMR, DFT calculations and mesoscopic models to improve our understanding of supercapacitors

C. Merlet 1 ,2

1 CIRIMAT, Université de Toulouse, CNRS, Bât. CIRIMAT, 118 route de Narbonne, 31 062 Toulouse cedex 9, France

2 Réseau sur le Stockage Électrochimique de l’Énergie (RS2E), Fédération de Recherche CNRS 3459, HUB de l’Énergie, rue Baudelocque, 80 039 Amiens, France

Supercapacitors are energy storage systems in which the energy is stored by ion adsorption at the electrode/electrolyte interface. In order to optimise these systems, it is important to characterise precisely the electrolyte structure at the interface and how it is affected by the application of a potential difference. In this talk I will focus on porous carbons, commonly used as electrodes in supercapacitors, and report on how lattice simulations can be used to model ion diffusion in carbon particles and predict the NMR spectra of such ions [1]. Lattice simulations have allowed us to estimate the size of aromatic domains in several disordered porous carbon materials [2] and to assess the relative importance of key factors on the in situ NMR spectra of electrolyte ions. To go beyond this, there is a need for a better description of the chemical shift of adsorbed species. Indeed, in the past, chemical shifts calculations were simply done on small planar aromatic molecules. I will show that for small aromatic molecules a perturbation approach applied on a simple Hückel Hamiltonian can give accurate results [3]. A study is ongoing to improve this model in order to make it suitable for periodic disordered carbons.

[1] C. Merlet, A. C. Forse, J. M Griffin, D. Frenkel and C. P. Grey, J. Chem. Phys., 142, 094701 (2015)

[2] A. C. Forse, C. Merlet, P. K. Allan, E. K. Humphreys, J. M Griffin, M. Aslan, M. Zeiger, V. Presser, Y. Gogotsi and C. P. Grey, Chem. Mater., 27, 6848 (2015)

[3] D. Kilymis, A. P. Bartók, C. J. Pickard, A. C. Forse and C. Merlet, Phys. Chem. Chem. Phys., 22, 13746 (2020)