(348e) Non-Faradic Energy Storage By Room Temperature Ionic Liquids in Nanoporous Electrodes

The enhancement of non-Faradic energy density stored by ionic electrolytes in nanostructured electrodes is an intriguing issue of great practical importance for energy storage in electric double layer capacitors (EDLC). Based on extensive molecular dynamics simulations of various carbon-based nanoporous electrodes and room temperature ionic liquid (RTIL) electrolytes we identify atomistic mechanisms and correlations between electrode/electrolyte structures that lead to capacitance enhancement. In the symmetric electrode setup with nanopores having atomically smooth walls, most RTILs showed up to 50% capacitance increase compared to infinitely wide pore.  Extensive simulations using asymmetric electrodes and pores with atomically rough surfaces demonstrated that tuning of electrode nanostructure could lead to further substantial capacitance enhancement. Therefore the capacitance in nanoporous electrodes can be increased due to a combination of two effects: i) the screening of ionic interactions by nanopore walls upon electrolyte nanoconfinement, and ii) the optimization of nanopore structure (volume, surface roughness) to take into account the asymmetry between cation and anion chemical structures. Our findings provide new insights into phenomena of energy storage by nanoconfined electrolytes and may guide the development of future materials for high energy density storage devices.