Events

Future events

Rss
NOV 20 2018

CIC energiGUNE's seminar "Towards safe and low cost high performance Na-O2 batteries"

Speaker: Dr. Cristina Pozo-Gonzalo

From: ARC Centre of Excellence for Electromaterials Science, IFM-Institute for Frontier Materials, Deakin University, Australia

 

The increasing energy demand requires new energy storage technologies to meet current and also future needs. Metal-O2 batteries are especially attractive due to their superior specific energy related to the use of a light metallic anode, and the use of oxygen as active materials in the cathode which is not stored within the battery. Among those chemistries, sodium-oxygen are attracting a great deal of attention due to their high specific energy (e.g. 1605 or 1108 Wh kg-1, depending on the final discharge product) 1 but also their low production cost and the abundance of sodium.2

On the other hand, ionic liquids are interesting alternative electrolytes due to their superior electrochemical and thermal stability, which enhances the overall safety of the battery3. Reports of the plating and stripping of sodium in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [C4mpyr][TFSI]4 exemplify their feasibility for secondary sodium batteries. Our main research is on comprehensive studies regarding the impact of the electrolyte composition on the oxygen reduction mechanism in order to deliver highly efficient rechargeable sodium-air batteries, using [C4mpyr][TFSI]. 5-6

Upon increasing the Na+ concentration in the electrolyte mixture, the O2/ O2- redox process becomes more efficient (e.g. 74%) and the onset potential of the reduction process shifts 0.35 V more positive due to a superior solvation of the superoxide anion (O2●-) by Na+.5 Radial distribution function (RDF) showed a significant decrease in the coordination number O2- - [C4mpyr]+ upon Na+ concentration increase due to the preference of O2- - Na+ coordination as already observed in the electrochemistry experiments.

Using a half cell device, we have observed that increasing the concentration of NaTFSI salt, from 1.13 to 16.6 mol%, in [C4mpyr][TFSI] bring a significant enhancement in the discharge capacity up to 10 times, reduction of the charge overpotential and also increase in long-term cyclability.7 The morphology of the deposits were investigated observing interesting differences. A film-like deposit was attained for the diluted electrolyte mixture, whereas dense coverage of spherical particles, ranging from nanometres to micron in diameter, was observed for the concentrated mixture.

Those differences on the deposit morphology, and then performance, were correlated with the coordination of Na+ by the anion of the IL ([TFSI]). In solutions with low Na+ concentration, Na+ is strongly coordinated by the anion of the IL, which decreases its mobility; however, at higher Na+ concentrations, this interaction is weaker, and mass transport is favoured before the deposition process. Such findings are extremely important from an applied perspective to understand the growth and morphology mechanism of the discharge products.

 

References:

1.             Bender, C. L.; Schroder, D.; Pinedo, R.; Adelhelm, P.; Janek, J., One- or Two-Electron Transfer? The Ambiguous Nature of the Discharge Products in Sodium-Oxygen Batteries. Angewandte Chemie 2016, 55 (15), 4640-9.

2.             Ha, S.; Kim, J. K.; Choi, A.; Kim, Y.; Lee, K. T., Sodium-Metal Halide and Sodium-Air Batteries. Chemphyschem 2014, 15 (10), 1971-1982.

3.             MacFarlane, D. R.; Tachikawa, N.; Forsyth, M.; Pringle, J. M.; Howlett, P. C.; Elliott, G. D.; Davis, J. H.; Watanabe, M.; Simon, P.; Angell, C. A., Energy applications of ionic liquids. Energy & Environmental Science 2014, 7 (1), 232-250.

4.             Mohd Noor, S. A.; Howlett, P. C.; MacFarlane, D. R.; Forsyth, M., Properties of sodium-based ionic liquid electrolytes for sodium secondary battery applications. Electrochimica Acta 2013, 114, 766-771.

5.             Pozo-Gonzalo, C.; Howlett, P. C.; MacFarlane, D. R.; Forsyth, M., Highly reversible oxygen to superoxide redox reaction in a sodium-containing ionic liquid. Electrochemistry Communications 2017, 74, 14-18.

6.             Pozo-Gonzalo, C.; Johnson, L. R.; Jónsson, E.; Holc, C.; Kerr, R.; MacFarlane, D. R.; Bruce, P. G.; Howlett, P. C.; Forsyth, M., Understanding of the Electrogenerated Bulk Electrolyte Species in Sodium-Containing Ionic Liquid Electrolytes During the Oxygen Reduction Reaction. The Journal of Physical Chemistry C 2017, 121 (42), 23307-23316.

7.             Zhang, Y. F.; Ortiz-Vitoriano, N.; Acebedo, B.; O'Dell, L.; MacFarlane, D. R.; Rojo, T.; Forsyth, M.; Howlett, P. C.; Pozo-Gonzalo, C., Elucidating the Impact of Sodium Salt Concentration on the Cathode Electrolyte Interface of Na-Air Batteries. J. Phys. Chem. C 2018, 122 (27), 15276-15286.

Ending data: 11.20.2018
  • Place: CIC energiGUNE, Seminar room, 12:00
  • We use our own and third-party cookies to analyse user browsing.

    Continuing browsing will imply acceptance of their use. The settings can be changed and further information can be found here.