Electrochemical capacitors (supercapacitors) are increasingly used in electronics, transportation, and grid storage applications. Most research strategies focus on expanding the voltage window, maximizing areal capacitance of electrodes, and increasing the operating temperature range. Although recent efforts have successfully investigated the relationship between pore size and electrolyte ion size, existing research does not describe the influence of electrode surface properties on capacitance and electrosorption dynamics. Experimental carbon electrode interfaces are not pristine and typically contain many features, including functional groups and defects. These surface features interact with electrolytes and influence orientation and ion densities in pores, localized mobilities during charge/discharge cycling, and electrochemical stability under applied potentials. Very few studies have investigated the influence of surface chemistry and structural order of carbon on key processes at the electrode-electrolyte interfaces. These efforts have yet to decouple the influence of ion confinement and comprehensively describe either the relative significance of surface defects in porous and non-porous systems or the process of ion partitioning in complex pore architectures. Our efforts focus on porous and non-porous carbons and decouple the influence of surface structure and chemistry on their interactions with electrolytes. We rely on carbide-derived carbons (CDCs) with well-controlled porosities; onion-like carbons and graphene act as model external surface systems for ion adsorption. We use chemical treatments and vacuum annealing procedures to selectively modify surface chemistry or graphitize electrodes. Neutron scattering probed the properties, orientations, filling densities, and dynamics of confined electrolytes, such as [Im+] and [Tf2N-]-containing ionic liquids. Electrochemical testing directly corresponded with confined ion dynamics and demonstrated improved charging dynamics on ionophilic electrode-electrolyte interfaces. We implemented electrolyte mixtures in unimodal and bimodal pore systems and showed how both device and electrolyte design may expand operating capabilities. Molecular dynamics provided key fundamental simulations of neutron scattering results and electrochemical measurements. We use these findings to maximize charge storage densities and rate handling capabilities of supercapacitors for novel energy storage systems.

Carbon-electrolyte interfaces and their effect on capacitive energy storage

251st National Meeting (2016)

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