Surface-active ionic liquids near the electrode surface: Development and influence on molecular dynamics simulations

To examine the changing self-assembled nanostructures of ionic liquid (IL)-based electrolytes during energy storage, electrolyte systems [P14,6,6,6][C8SO4], [N8888][C8SO4], [P4444][C8SO4], [C6mim][C8SO4], [P14,6,6,6][AOT], [Bpyr][AOT], [BMpy][AOT], [Bpip][AOT], and [Cnmim][AOT] (n = 2, 4, 6, 8, 10 and 12) were investigated using molecular dynamics simulations. The catanionic surface-active ILs (SAILs) had been used as electrolytes or components of electrolytes in supercapacitors and batteries over a wide range of temperatures, exhibiting superior performance than nonamphiphilic ILs. However, catanionic SAILs were inferior in terms of energy storage effect compared to SAILs with unsaturated heterocyclic structures. Our study showed that SAILs with unsaturated heterocycles structure exhibit unique charging processes and different performances for energy storage owing to different cation nanostructures near negative electrodes. The unsaturated heterocycles exhibited a high tendency to be oriented in parallel to the electrode plate, increasing the Coulombic interaction between the layers of the cations and the electrode surface and bringing additional cations closer to the electrode. This arrangement increases the probability of obtaining a greater energy density compared to other saturated heterocyclic SAILs or catanionic SAILs that have W-shaped cations close to the negative electrode.