Simulation of Propylene Carbonate As Solvent for Electrochemical Double-Layer Capacitors

Simulation of Propylene Carbonate as Solvent for

Electrochemical Double-layer Capacitors

X. You, L. R. Pratt, and N. Pesika

Abstract    Propylene carbonate (PC) is a popular choice of solvent for electric double-layer capacitors (EDLCs).^1,2 Despite recent encouraging simulations of EDLCs³ based on carbon nanotube forests, thorough testing of the required force-field features has not been available. Recent work^3,4 shows that the modeled liquid PC completely wets a planar graphite surface (contact angle,  =0), in disagreement with experimental droplet formation ( =37°). Empirical adjustment of PC:graphite attractive interactions brings those results into agreement. Molecular dynamics simulations of PC droplets, bulk PC liquid, and a saturated solution of tetraethylammonium tetrafluoroborate in PC, using the GROMACS package, further characterize the assumed force-field. We present and discuss a range of interfacial properties including surface tensions, and their temperature and concentration dependences. We consider the applicability of the Kelvin equation, describing the vapor pressure of small droplets, for evaluating the curvature dependence of surface tension. ⁵

FIG: (left) Interfacial density profiles and simulation geometry for slab calculation of 1000 PC with 85 tetraethylammonium and 85 tetrafluoroborate at 300K. Compared with pure PC (surface tension = 40.8erg/cm2), the ionic material increases the surface tension to 41.5erg/cm².  (right) Simulation configuration of a droplet with 600 PC molecules.

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2.      Yang, L., Fishbine, B. H., Migliori, A., and Pratt, L. R. J. Chem. Phys. 132, 044701 (2010).

3.      W. Zhang, G. G. Hoffman¹, L. R. Pratt¹, N. Pesika¹, K. M.  Aritakula² and S. W. Rick²(¹Tulane University, ²University of New Orleans 2012)

4.      "Simulation of Propylene Carbonate as Solvent for Electrochemical Double-layer Capacitors", Hoffman, G. G., Mariano, R., Pesika, N., Pratt, L. R., Rick, S. W., and X. You (Proc. LA EPSCoR RII LA-SiGMA 2011 Symp.), p 101-104.

5.      Powles, J. G., Fowler, R. F., and Evans, W. A. B. Chem. Phys. Letts. 76, 289 (1983).