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Novel Na+ Ion diffusion mechanism in mixed organic-inorganic ionic liquid electrolyte leading to high Na+ transference number and stable, high rate electrochemical cycling of sodium cells

Forsyth, Maria, Yoon, Hyungook, Chen, Fangfang, Zhu, Haijin, MacFarlane, Douglas R., Armand, Michel and Howlett, Patrick C. 2016, Novel Na+ Ion diffusion mechanism in mixed organic-inorganic ionic liquid electrolyte leading to high Na+ transference number and stable, high rate electrochemical cycling of sodium cells, Journal of physical chemistry C, vol. 120, no. 8, pp. 4276-4286, doi: 10.1021/acs.jpcc.5b11746.

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Title Novel Na+ Ion diffusion mechanism in mixed organic-inorganic ionic liquid electrolyte leading to high Na+ transference number and stable, high rate electrochemical cycling of sodium cells
Author(s) Forsyth, Maria
Yoon, Hyungook
Chen, Fangfang
Zhu, HaijinORCID iD for Zhu, Haijin orcid.org/0000-0001-6352-7633
MacFarlane, Douglas R.
Armand, Michel
Howlett, Patrick C.ORCID iD for Howlett, Patrick C. orcid.org/0000-0002-2151-2932
Journal name Journal of physical chemistry C
Volume number 120
Issue number 8
Start page 4276
End page 4286
Total pages 11
Publisher American Chemical Society
Place of publication Washington, D.C.
Publication date 2016
ISSN 1932-7447
1932-7455
Keyword(s) Science & Technology
Physical Sciences
Technology
Chemistry, Physical
Nanoscience & Nanotechnology
Materials Science, Multidisciplinary
Chemistry
Science & Technology - Other Topics
Materials Science
N-METHYLPYRROLIDINIUM BIS(FLUOROSULFONYL)IMIDE
SECONDARY BATTERIES
SELF-DIFFUSION
TEMPERATURE
TRANSPORT
SOLUTES
Summary Ambient temperature sodium batteries hold the promise of a new generation of high energy density, low-cost energy storage technologies. Particularly challenging in sodium electrochemistry is achieving high stability at high charge/discharge rates. We report here mixtures of inorganic/organic cation fluorosulfonamide (FSI) ionic liquids that exhibit unexpectedly high Na+ transference numbers due to a structural diffusion mechanism not previously observed in this type of electrolyte. The electrolyte can therefore support high current density cycling of sodium. We investigate the effect of NaFSI salt concentration in methylpropylpyrrolidinium (C3mpyr) FSI ionic liquid (IL) on the reversible plating and dissolution of sodium metal, both on a copper electrode and in a symmetric Na/Na metal cell. NaFSI is highly soluble in the IL allowing the preparation of mixtures that contain very high Na contents, greater than 3.2 mol/kg (50 mol %) at room temperature. Despite the fact that overall ion diffusivity decreases substantially with increasing alkali salt concentration, we have found that these high Na+ content electrolytes can support higher current densities (1 mA/cm2) and greater stability upon continued cycling. EIS measurements indicate that the interfacial impedance is decreased in the high concentration systems, which provides for a particularly low-resistance solid-electrolyte interphase (SEI), resulting in faster charge transfer at the interface. Na+ transference numbers determined by the Bruce-Vincent method increased substantially with increasing NaFSI content, approaching >0.3 at the saturation concentration limit which may explain the improved performance. NMR spectroscopy, PFG diffusion measurements, and molecular dynamics simulations reveal a changeover to a facile structural diffusion mechanism for sodium ion transport at high concentrations in these electrolytes.
Language eng
DOI 10.1021/acs.jpcc.5b11746
Field of Research 030301 Chemical Characterisation of Materials
030304 Physical Chemistry of Materials
030604 Electrochemistry
Socio Economic Objective 850602 Energy Storage (excl. Hydrogen)
HERDC Research category C1 Refereed article in a scholarly journal
ERA Research output type C Journal article
Copyright notice ©2016, American Chemical Society
Persistent URL http://hdl.handle.net/10536/DRO/DU:30082973

Document type: Journal Article
Collection: Institute for Frontier Materials
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