Toward New Solvents for EDLCs: From Computational Screening to Electrochemical Validation

Abstract

The development of innovative electrolytes is a key aspect of improving electrochemical double layer capacitors (EDLCs). New solvents, new conducting salts as well as new ionic liquids need to be considered. To avoid time-consuming "trial and error" experiments, it is desirable to "rationalize" this search for new materials. An important step in this direction is the systematic application of computational screening approaches. Via the fast prediction of the properties of a large number of compounds, for instance all reasonable candidates within a given compound class, such approaches should allow to identify of the most promising candidates for subsequent experiments. In this work we consider the toy system of all reasonable nitrile solvents up to 12 heavy atoms. To investigate if our recently proposed computational screening strategy is a feasible tool for the purpose of rationalizing the search for new EDLC electrolyte materials, we correlatein the case of EDLCs for the first timecomputational screening results with experimental findings. For this, experiments are performed on those compounds for which experimental data is not available from the literature. We find that our screening approach is well suited to pick good candidates out of the set of all reasonable nitriles, comprising almost 5000 compounds.

Predictions of Physicochemical Properties of Ionic Liquids with DFT

“…Density functional theory (DFT) computational methods are widely applied to calculate the electronic properties of ionic liquids on the case-by-case basis. Meanwhile, the so-called high-throughput approach is applied to conduct screening of components of aqueous and organic solvent electrolytes in search for the best candidates for their practical applications [3][4][5][6][7][8][9], for example, in the so-called electrolyte genome project [10]. However, this approach has not yet been fully applied for screening ionic liquids.…”

“…Then, the process is repeated on a smaller number of candidates, and usually using accurate methods. The high-throughput approach was used to find the best components for energy storage systems [3][4][5][6][7][8][9][10]. Cheng et al screened 1400 organic molecules for use in non-aqueous redox-flow batteries [11]; they down-selected the candidates using DFT-based descriptors for redox potentials, solubility, and stability.…”

Molecular modelling of carbon/ionic liquid interfaces for electric double – layer capacitors

“…Computational screening approaches have therefore recently been proposed to tackle this difficult problem. 67 Interestingly, the capacitance dependence observed here contrasts quite strongly with the results in Chapter 4, which showed strong capacitance dependence on the concentration of ACN. The origin of the difference observed could occur from either, or a combination of, fundamental differences in the electrode structures, or inaccuracies of the CDC model in capturing real behaviour.…”

“…31 Interestingly, the observed capacitance of Ti CDC-950 exceeded that of Ti CDC-1200 by 43% 31 , even though the PSD and average pore diameters were similar (0.93 nm and 0.95 nm). 67 This indicates that local structure can affect the capacitance, since the smaller capacitance of Ti CDC-1200 was correlated with higher occurrences of graphitic zones.…”

“…Simulations that use accurate electrodes in combination with well-validated all-atom or coarse-grained electrolyte models is critical for future research that aims to provide further insight into the complex EDL phenomena that occurs at the confined RTIL -nanoporous electrode interface. Keeping up with material researchers who are consistently producing novel electrode materials is a challenging area for simulation researchers due to the large effort required to accurately reproduce electrode models of complex structures [67][68] and is worthy of more focus.…”