Title：Strategies of performance enhancement for supercapacitors operating at low temperature
Speaker：Xuehang Wang
Department of Materials Science and Engineering, A. J. Drexel Nanomaterials Institute, Drexel University, Philadelphia, PA 19104, USA
Time：
January 7, 2019 (Monday) 14:00-16:00
Venue：Conference Room on 9th Floor, Tang Aoqing Building, Central Campus
Abstract：
An extension of reliable operation temperature for an electrical energy storage device is required by specialized application, such as oil industry, military use, space exploration and electric vehicles.1-2 Supercapacitor, which stores charges electrostatically, is more suitable for low temperature applications, since the operation of batteries below -30 oC is limited by its faradic charge storage mechanism. Ionic liquids are attractive electrolytes for supercapacitors, because their good (electro-)/chemical stability brings about good safety, large voltage window and large energy density. However, supercapacitors using ionic liquid as electrolyte, suffer substantial drop of capacitance at low temperature. This is because a large fraction of small pores is not accessible by electrolyte ions, especially for ionic liquid with low ionic mobility and large ion size.3
To enhance the performance of 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 doping IL with 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 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.
With a fast development of electrode material for supercapacitor, the choice of material extends from mainly activated carbon to many other 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 temperature.
Reference
1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
