Classical Density Functional Theory Insights for Supercapacitors

Abstract

The most urgent issue for supercapacitor is to improve their energy density so that they can better compete with batteries. To design materials and interfaces for supercapacitor with higher energy density requires a deeper understanding of the factors and contributions affecting the total capacitance. In our recent works, the classical density functional theory (CDFT) was developed and applied to study the electrode/electrolyte interface behaviors, to understand capacitive energy storage. For porous electrode materials, we studied the pore size effect, curvature effect, and the surface modification of porous materials on the capacitance. Thought CDFT, we have found that the curvature effects on convex and concave EDLs are drastically different and that materials with extensive convex surfaces will lead to maximized capacitance; CDFT also predicts oscillatory variation of capacitance with pore size, but the oscillatory behavior is magnified as the curvature increases; an increase in the ionophobicity of the nanopores leads to a higher capacity for energy storage, and a pore-like impurity can enter the pore, makes the pore ionophobic and storage more energy. We also find the mixture effect, which makes more counterions pack on and more co-ions leave from the electrode surface, leads to an increase of the counterion density within the EDL and thus alargercapacitance.

Classical dynamical density functional theory: from fundamentals to applications

“…[333,356,474]. Finally, electrochemical systems containing ions of different charge [53,184,185,192,349,354,414,415,[475][476][477][478][479][480][481][482][483][484][485] are an important application of DDFT for mixtures (see Section 8.1.10). An option for future work is the investigation of systems with nonreciprocal interactions [547].…”

“…Impedance resonance can be studied by analyzing the effects of a time-dependent external electric field on the ions in DDFT [53]. Further applications include reversible heating [484], viscosity effects [185], ion dynamics in nanopores [480,485,977], and colloid-interface interactions [354]. Lee et al [978] mentioned the assumption that the ion density is low compared to the solvent density as a limitation of DDFT.…”

Theory and Simulations of Ionic Liquids in Nanoconfinement

“…We refer the interested readers to a review by Hartel, 178 which covers the application of DFT to confined ILs before 2017, with a particular focus on technicalities. There is also a more recent review by Lian and Liu, 179 who mainly focused on their own contribution.…”

Ion Desolvation in Microporous Electrodes with Liquid Electrolytes

“…CDFT has been applied to predict the capacitances by accurately accounting for the excluded volume effect and electrostatic correlation in confined simple electrolytes. [38][39][40] By combining the MDFT and CDFT, the ion desolvation and its contribution to the capacitance of the microporous electrodes are investigated. We show that this combination can unravel the ion desolvation effect to electrochemical properties, and give satisfactory predictions on the capacitances of practical microporous electrodes with liquid electrolytes as long as the pore size distribution (PSD) is provided.…”