An asymmetric MnO2|activated carbon supercapacitor with highly soluble choline nitrate-based aqueous electrolyte for sub-zero temperatures

Sandra Schrade, Zijian Zhao, Zhazira Supiyeva, Xinman Chen, Sonia Dsoke, Qamar Abbas*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

MnO2|activated carbon supercapacitors are attractive power devices that rival the electric double-layer capacitors (EDLCs) due to high reachable voltage. However, they greatly suffer from performance loss at low temperature as most of aqueous electrolytes freeze below ca. -10°C. Here, a concentrated choline nitrate-based (5 mol/L aqueous ChNO3) electrolyte is applied to extend the working temperature range due to its eutectic-like properties. In such electrolyte, water acts as hydrogen bond donor for nitrate anion and low hydration energy for large choline cations favors ionic transport. The MnO2/CNT composite electrode with a hierarchical structure has been synthesized by hydrothermal process. The presence of CNTs as core component facilitates the electron conduction, while the two-dimensional MnO2 flakes grown on the surface provide electrolyte transport pathways and improve the interfacial processes (pseudocapacitive charge/discharge). Thanks to the low hydration of choline cation, the individual activated carbon (AC, negative) and MnO2/CNT (positive) electrodes are charged symmetrically up to a cell voltage of 1.8 V. Overall, due to the wide electrochemical stability window (∼2.0 V) and anti-freezing properties of ChNO3-based aqueous electrolyte and the hierarchical design of the MnO2/CNT composite, the asymmetric supercapacitor operates down to -40 °C and displays excellent energy and coulombic efficiency with no loss of performance after several thousand cycles. This work provides a new possibility on the low temperature application of high voltage supercapacitors.

Original languageEnglish
Article number140708
JournalElectrochimica Acta
Volume425
DOIs
Publication statusPublished - 1 Sept 2022

Keywords

  • Choline nitrate
  • CNTs
  • Low temperature
  • MnO
  • Pseudocapacitance
  • Supercapacitor

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Electrochemistry

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