Hunting ionic liquids with large electrochemical potential windows

Abstract

Ionic liquids (ILs) with large electrochemical potential windows (EPWs) are ideally suited to improve the energy and power density of electrical devices for energy storage. However, guidelines are scarcely available for the selection or systematic screening of ILs for practical applications. Here, we present theoretical predictions for the EPW of thousands of cation‐anion pairs based on a long‐range corrected hybrid density functional theory. The cathodic and anodic potential limits were estimated from the highest occupied molecular orbital and lowest unoccupied molecular orbital energies of individual cations and anions. The approximate method predicts EPWs in reasonable agreement with existing experimental data for several commonly used ionic systems and can be used as a screening tool for a large library of ILs. Five most stable anions, with the cathode stability in the order of B[CN]4 > PF6 > BF4 > BOB>NTf2, have been identified. These anions provide the largest EPWs when they are paired with conventional organic cations. The cation stability is reduced upon elongation of the alkyl chain length or branching of the molecular backbone. © 2018 American Institute of Chemical Engineers AIChE J, 65: 804–810, 2019

Nanoporous carbon for electrochemical capacitive energy storage

“…Recently, DFT calculation has been applied to predict the electrochemical potential windows for ionic liquids to accelerate the process for experimental selection. 358 Theoretical and experimental works have shown that unlike solvated electrolytes, the EDL structure of ionic liquids does not align with the classic EDL models (for details of the model see Section 2.1). 36,41,359 In ionic liquids, the existence of ion pairs and compact packing of ions result in a short-to long-range of electrostatic force based on the applied voltage.…”

Boron: Its Role in Energy‐Related Processes and Applications

“…As mentioned above, a low dynamic viscosity is a prerequisite for electrolytes because it is paralleled by a high ion mobility, as evident from a high specific conductivity. Tetracyanoborate‐ILs ( TCB ‐ILs, Figure ) were the first cyanoborate‐ILs that were synthesized and applied for electrochemical devices, for example, DSSCs . Later, applications in batteries and supercapacitors were also studied .…”

Bor in energiebezogenen Prozessen und Anwendungen

“…Wie bereits erwähnt, ist eine niedrige dynamische Viskosität eine Grundvoraussetzung für eine erfolgreiche Anwendung als Elektrolyt, da diese mit einer hohen Ionenmobilität und damit verbunden mit einer hohen spezifischen Leitfähigkeit einhergeht. Tetracyanoborat‐ILs ( TCB ‐ILs, Abbildung ) waren die ersten Cyanoborat‐Ils, die dargestellt und erfolgreich in elektrochemischen Vorrichtungen wie DSSCs eingesetzt werden konnten. In der Folge wurde das Anwendungsspektrum von TCB ‐ILs auf Batterien und Superkondensatoren ausgeweitet und in den letzten Jahren konnten zahlreiche weitere Cyanoboratanionen und deren ILs realisiert und im Detail untersucht werden.…”