To enhance the performance of a supercapacitor with ionic liquid electrolyte at low temperature, studies have been focusing on facilitating ion accessibility to the electrode porous structure. Mitigating the Coulomb ion pairing (anion-cation attraction), such as adding organic solvent and binary mixture of ionic liquid or eutectic electrolyte, has been used to establish sufficient fluidity and improve ions mobility of electrolytes at low temperatures.4 Combining two different species of cations and only one anion mixtures (or vice versa) can lower the melting point of ionic mixture to -80 oC.5 In addition, adjusting the morphology of the electrode material is another way to enhance the ion transportation dynamically. For example, with larger inter-tube distance and more open porous structure, carbon nanotube showed a much better rate performance than that of the onion-like carbon at the temperature of -50 oC. Similarly accessible pore structures ae required for operation of organic electrolytes at low temperatures.
With a fast development of electrode materials for supercapacitor, the choice of material extends from activated carbons, carbide-derived carbons, graphene, carbon onions and nanotubes, to many pseudocapacitive materials (carbides, nitrides, oxides, etc.), and the morphology of the material also varies in dimensions and confinement. Many unique electrolyte ion behaviors have been found or are waiting to be found in various electrode material with specific physical and chemical properties. Hence, a proper design of electrode material in conjunction with an electrolyte formulation will offer many opportunities for enhancing the supercapacitor performance at low temperatures.
Reference
- Lin, X.; Salari, M.; Arava, L. M. R.; Ajayan, P. M.; Grinstaff, M. W., High temperature electrical energy storage: advances, challenges, and frontiers. Chemical Society Reviews 2016, 45 (21), 5848-5887.
- Huang, P.; Pech, D.; Lin, R.; Mcdonough, J. K.; Brunet, M.; Taberna, P.-L.; Gogotsi, Y.; Simon, P., On-chip micro-supercapacitors for operation in a wide temperature range. Electrochemistry Communications 2013, 36, 53-56.
- Abbas, Q.; Béguin, F., High voltage AC/AC electrochemical capacitor operating at low temperature in salt aqueous electrolyte. Journal of Power Sources 2016, 318, 235-241.
- Tsai, W.-Y.; Lin, R.; Murali, S.; Zhang, L. L.; McDonough, J. K.; Ruoff, R. S.; Taberna, P.-L.; Gogotsi, Y.; Simon, P., Outstanding performance of activated graphene based supercapacitors in ionic liquid electrolyte from− 50 to 80 C. Nano Energy 2013, 2 (3), 403-411.
- Lin, R.; Taberna, P.-L.; Fantini, S.; Presser, V.; Pérez, C. R.; Malbosc, F.; Rupesinghe, N. L.; Teo, K. B.; Gogotsi, Y.; Simon, P., Capacitive energy storage from− 50 to 100 C using an ionic liquid electrolyte. The Journal of Physical Chemistry Letters 2011, 2 (19), 2396-2401.