Computational Screening of Supercapacitors

In order to be self-sufficient with relatively constant energy output, renewable energy sources, such as solar and wind, require that energy be stored during periods of high energy production so that it can be available during periods of low or zero energy production. Among the many choices for energy storage devices, electrical double layer capacitors (EDLCs), also called supercapacitors, are attracting considerable attention. Supercapacitors store electrical energy via ion electrosorption directly in the EDLs at the electrolyte-electrode interface, suggesting that such liquid-solid interfaces play a dominant role in the underlying energy storage mechanism and the resulting device performance. Because electrical energy in supercapacitors is stored based on physical phenomena rather than chemical reaction (as in batteries), supercapacitors have fast rates of charge/discharge and a virtually limitless number of charge cycles (unlike batteries, which are often limited to 10⁴ or less cycles). Much of the goal of supercapacitor research is aimed at increasing the amount of energy stored (energy density is the strong point in favor of batteries), which in turn focuses attention on the electrolyte, the nature of the electrode, and the electrode-electrolyte interactions. In recent years, ionic liquids (ILs) have become emerging candidates for electrolytes used in supercapacitors, due to their exceptionally wide electrochemical window, excellent thermal stability, nonvolatility, and relatively inert nature; meanwhile carbons are the most widely used electrode materials in supercapacitors, due to their high specific surface area, good electrical conductivity, chemical stability in a variety of electrolytes, and relatively low cost. More recently, 2D materials known as MXenes (consisting of alternating layers of carbon and transition metal) have emerged as viable and versatile electrode materials. 

For many years, we have been using molecular modeling combined with molecular experimental probes, such as SAXS, SANS, NMR, and AFM, to investigate the interfacial phenomena occurring between the IL electrolytes and electrodes of varying geometries to understand the energy storage mechanism of supercapacitors that rely on EDLs established at IL-electrode interfaces.

Recently, we developed a molecular simulation protocol for simulating supercapacitors at constant applied electrical potential. With this protocol in hand, we are in a position to screen the supercapacitance performance of a variety of electrolyte/electrode combinations to investigate optimal supercapacitor designs. The student will implement this screening approach.