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Elucidating the impact of sodium salt concentration on the cathode-electrolyte interface of Na-Air batteries
journal contribution
posted on 2018-07-12, 00:00 authored by Yafei Zhang, N Ortiz-Vitoriano, B Acebedo, Luke O'DellLuke O'Dell, D R Macfarlane, T Rojo, Maria ForsythMaria Forsyth, Patrick HowlettPatrick Howlett, Cristina Pozo-GonzaloCristina Pozo-GonzaloA 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 of the overpotential and an increase in long-term cyclability. Additionally, a distinct discharge morphology is also observed, which is demonstrated to be a result of a different oxygen reduction reaction (ORR) 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 Na+ concentrations, Na+ is strongly coordinated by 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 favouring mass transport prior to product deposition. It therefore appears that the "highly-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 cubic morphology which is typical of NaO2. This is the first work where this characteristic morphology appears when using an ionic liquid which opens new venues for future research.
History
Journal
Journal of physical chemistry CVolume
122Issue
27Pagination
15276 - 15286Publisher
American Chemical SocietyLocation
Washington, D.C.Publisher DOI
ISSN
1932-7447eISSN
1932-7455Language
engPublication classification
C1 Refereed article in a scholarly journalCopyright notice
2018, American Chemical SocietyUsage metrics
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Categories
Keywords
Na–O2 cellionic liquidpyrrolidiniumelectrolytehalf-cellsodium saltScience & TechnologyPhysical SciencesTechnologyChemistry, PhysicalNanoscience & NanotechnologyMaterials Science, MultidisciplinaryChemistryScience & Technology - Other TopicsMaterials ScienceIONIC LIQUID ELECTROLYTESNA-O-2 BATTERIESOXYGEN REDUCTIONLI-O-2 BATTERIESHIGH-CAPACITYSPECTROSCOPYNUCLEATIONMECHANISMDISCHARGEPRODUCTS