Energy and power performances of binary mixtures of ionic liquids in planar and porous electrodes by molecular dynamics simulations

PHL Ferreira and AM Sampaio and LJA Siqueira, ELECTROCHIMICA ACTA, 410, 139982 (2022).

DOI: 10.1016/j.electacta.2022.139982

Binary mixtures of ionic liquids are interesting alternatives to tailor ionic liquids properties. Some of them have been proposed as electrolytes for supercapacitors. Herein, we performed molecular dynamics simulations of planar and porous electrodes with binar y mixtures of ionic liquids comprising the 1-ethyl-3-methyl- imidazoliumbis(trifluoromethane-sulfonyl)imide (EMIMNTf2) and 1-ethyl-3-methyl-imidazoliumtetrafluoroborate (EMIM BF4), increasing the mole fraction of the latter (xBF4) from 0 to 1. The energy densities calculated from the simulations increase monotonically with x(BF4), accordingly with available experimental results Angew. Chem. Int. Ed. 2015, 54, 1 - 5. Considering that the electrode simulations were dealt with the constant potential model, the characteristic charging times were calculated for planar and porous electrodes. The devices containing only EMIM NTf2 charge slower than electrolytes with x(BF4) > 0.0, and the fastest charging happens inx(BF4) = 1.0 V. These features are related to the higher NTf2-electrode interaction and also to the smaller size of BF4(-). For porous electrode, the calculated Ragone plot indicates that EMIMBF4 outperforms a l l the other electrolytes with a voltage of 3.0 V in terms of energ y and power densities. In the system of best performance, there are considerable contributions of co- ion desorption and counter-ion adsorption mechanisms in the negative and positive electrodes, respectively.

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