Al(TFSI)₃ as a Conducting Salt for High-Voltage Electrochemical Double-Layer Capacitors

In this study, we report for the first time about the use of aluminum bis­(trifluoromethanesulfonyl)­imide [Al­(TFSI)₃] as conducting salt for electrochemical double-layer capacitors (EDLCs). We show that using this salt it is possible to realize highly concentrated electrolytes, which are able to suppress the anodic dissolution of the aluminum current collectors. Because of this ability, the use of this electrolyte makes possible the realization of EDLCs that can retain 80% of their initial performance after floating for 1500 h at 3 V (which is comparable to ∼5000000 cycles of charge and discharge at 1 A g^–1)

Structural Investigations on Lithium-Doped Protic and Aprotic Ionic Liquids

Solutions of lithium bis­(trifluoromethanesulfonyl)­imide (LiNTf₂), in four different [NTf₂]⁻-based ionic liquids, are extensively investigated as potential electrolytes for lithium-ion batteries. Solvation of the [Li]⁺ ions in the ionic liquids and its impact on their physicochemical properties are studied herein with the aid of molecular dynamics simulations. The cationic components of the investigated liquids were systematically varied so as to individually evaluate effects of specific structural changes; increase in ring size, the addition of an alkyl chain and absence of an acidic proton, on the solvation and mobility of the [Li]⁺ cations. The studied cations also allow for a direct comparison between solutions of [Li]⁺ salt in protic and aprotic ionic liquids. Emphasis is laid on elucidating the interactions between the [Li]⁺ and [NTf₂]⁻ ions revealing slightly higher coordination numbers for the aprotic solvent, benchmarked against experimental measurements. The study suggests that the ionic liquids largely retain their structure upon salt addition, with interactions within the liquids only slightly perturbed. The rattling motion of the [Li]⁺ cations within cages formed by the surrounding [NTf₂]⁻ anions is examined by the analysis of [Li]⁺ autocorrelation functions. Overall, the solvation mechanism of [Li]⁺ salt, within the hydrogen-bonded network of the ionic liquids, is detailed from classical and <i>ab initio</i> molecular dynamics simulations

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

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

Insights into Bulk Electrolyte Effects on the Operative Voltage of Electrochemical Double-Layer Capacitors

Electrochemical double-layer capacitors (EDLCs) are robust, high-power, and fast-charging energy storage devices. Rational design of novel electrolyte materials could further improve the performance of EDLCs. Computational methods offer immense scope in aiding the development of such materials. Trends in experimentally observed operative voltages nevertheless remain difficult to predict and understand. We discuss here the intriguing case of adiponitrile (ADN) versus 2-methyl-glutaronitrile (2MGN) based electrolytes, which result in very different operative voltages in EDLCs despite structural similarity. As a preliminary step, bulk electrolyte effects on electrochemical stability are investigated by <i>ab initio</i> molecular dynamics (AIMD) and static, cluster-based quantum chemistry calculations