Elucidating the Impact of Sodium Salt Concentration on the Cathode-Electrolyte Interface of Na-Air Batteries

Yafei Zhang, Nagore Ortiz-Vitoriano, Begoña Acebedo, Luke O'Dell, Douglas R. MacFarlane, Teófilo Rojo, Maria Forsyth, Patrick C. Howlett, Cristina Pozo-Gonzalo

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7 Citations (Scopus)

Abstract

A promising approach to improve the specific capacity and cyclability in a Na-O2 cell using a pyrrolidinium-based ionic liquid electrolyte in a half-cell has been explored in this work. Increasing the concentration of sodium salt in an ionic liquid electrolyte produces a significant enhancement in the discharge capacity of up to 10 times, a reduction in the overpotential and an increase in the long-term cyclability. Additionally, a distinct discharge morphology is also observed, which is demonstrated to be result of a different oxygen reduction reaction mechanisms. These improvements are likely due to the solvation of Na+ in the electrolyte mixtures containing different Na+ concentrations; the coordination of Na+ by the anion of the ionic liquid dictates the discharge product morphology. At low concentrations, Na+ is strongly coordinated to the anion of the ionic liquid, and this also can have an effect on its mobility; however, at high Na+ concentration, this interaction is weakened and favors mass transport before product deposition. It therefore appears that the concentrated electrolyte strategy is a useful route to enhance the performance of Na-O2 batteries. Interestingly, when using a pressurized Swagelok-type cell, the discharge product presents a cubic morphology, which is typical of NaO2. This is the first work where this characteristic morphology appears when using an ionic liquid, opening new venues for future research.

Original languageEnglish
Pages (from-to)15276-15286
Number of pages11
JournalJournal of Physical Chemistry C
Volume122
Issue number27
DOIs
Publication statusPublished - 12 Jul 2018

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