Charge storage mechanism of α-MnO2 in protic and aprotic ionic liquid electrolytes

S. Lindberg, S. Jeschke, Piotr Jankowski, M. Abdelhamid, T. Brousse, J. Le Bideau, P. Johansson, A. Matic*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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In this work we have investigated the charge storage mechanism of MnO2 electrodes in ionic liquid electrolytes. We show that by using an ionic liquid with a cation that has the ability to form hydrogen bonds with the active material (MnO2) on the surface of the electrode, a clear faradaic contribution is obtained. This situation is found for ionic liquids with cations that have a low pKa, i.e. protic ionic liquids. For a protic ionic liquid, the specific capacity at low scan rate rates can be explained by a densely packed layer of cations that are in a standing geometry, with a proton directly interacting through a hydrogen bond with the surface of the active material in the electrode. In contrast, for aprotic ionic liquids there is no interaction and only a double layer contribution to the charge storage is observed. However, by adding an alkali salt to the aprotic ionic liquid, a faradaic contribution is obtained from the insertion of Li+ into the surface of the MnO2 electrode. No effect can be observed when Li+ is added to the protic IL, suggesting that a densely packed cation layer in this case prevent Li-ions from reaching the active material surface.

Original languageEnglish
Article number228111
JournalJournal of Power Sources
Number of pages8
Publication statusPublished - 2020


  • Hybrid
  • Ionic liquid
  • MnO2
  • Protic
  • Supercapacitor


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