Ion Bridging by Carbon Dioxide Facilitates Electrochemical Energy Storage at Charged Carbon–Ionic–Liquid Interfaces

Affiliation
Institute of Environmental Science and Engineering, School of Metallurgy and Environment Central South University Changsha 410083 P. R. China
Liu, Mingren;
Affiliation
Department of Materials and Environmental Chemistry Arrhenius Laboratory Stockholm University Stockholm SE‐106 91 Sweden
Wang, Yong‐Lei;
GND
1258897423
Affiliation
Institute for Technical Chemistry and Environmental Chemistry Center for Energy and Environmental Chemistry Jena (CEEC Jena) Friedrich‐Schiller‐University Jena Philosophenweg 7a 07743 Jena Germany
Schutjajew, Konstantin;
Affiliation
Institute of Environmental Science and Engineering, School of Metallurgy and Environment Central South University Changsha 410083 P. R. China
Chai, Liyuan;
GND
1070230448
ORCID
0000-0003-2377-1214
Affiliation
Institute for Technical Chemistry and Environmental Chemistry Center for Energy and Environmental Chemistry Jena (CEEC Jena) Friedrich‐Schiller‐University Jena Philosophenweg 7a 07743 Jena Germany
Oschatz, Martin

Abstract Solvent free ionic liquid (IL) electrolytes facilitate high‐voltage supercapacitors with enhanced energy density, but their complex ion arrangement and through that the electrochemical properties, are limited by strong Coulombic ordering in the bulk state and like‐charged ion repulsion at electrified interfaces. Herein, a unique interfacial phenomenon resulting from the presence of carbon dioxide loaded in 1‐Ethyl‐3‐methylimidazoliumtetrafluorborate electrolyte that simultaneously couples to IL ions and nitrogen‐doped carbonaceous electrode is reported. The adsorbed CO 2 molecule polarizes and mitigates the electrostatic repulsion among like‐charged ions near the electrified interface, leading to an ion “bridge effect” with increased interfacial ionic density and significantly enhanced charge storage capability. The unpolarized CO 2 possessing a large quadrupole moment further reduces ion coupling, resulting in higher conductivity of the bulk IL and improved rate capability of the supercapacitor. This work demonstrates polarization‐controlled like‐charge attraction at IL–electrode–gas three‐phase boundaries, providing insights into manipulating complex interfacial ion ordering with small polar molecule mediators.

Solvent‐free ionic liquid (IL) electrolytes enable high‐voltage and high‐energy‐density applications. The proposed bridge effect with CO 2 loaded in an IL electrolyte acting as a mediator on the nitrogen‐doped electrode surface, alleviates the undesired Coulombic ordering and interfacial like‐charged ion repulsion. By breaking the limitation of interfacial ion packing density, this effect results in a significant enhancement of charge storage capability. image

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