Supporting Information
Performance Enhancement and Mechanistic Studies of Room-Temperature SodiumSulfur Batteries with a Carbon-Coated Functional Nafion Separator and a
Na2S/Activated Carbon Nanofiber Cathode
Xingwen Yu and Arumugam Manthiram*
Materials Science and Engineering Program & Texas Materials Institute
The University of Texas at Austin
Austin, TX 78712, USA
Table S1. Maximum Van der Waals diameter of the sodium polysulfide species estimated
from the ionic radii of sulfur and sodium, the length of the S-S bond, and the length of the NaS bond (The relevant data for estimation are from wikipedia). The maximum van der Waals
diameter of the polysulfide species was calculated by considering that the polusulfide
melecules exist as a straight-line structure without any bond angles. For instance: the
maximum van der Waals size of the Na2S4 is estimated through the sum of bond-lengths of 3
S-S bonds, 2 Na-S bonds, and 2 ionic radii of Na ions ((3*0.205) + (2*0.143) + (2*0.099) =
1.099 nm).
Ionic radius, nm
Bond length, nm
Maximum Van der
Waals diameter, nm
Na+
0.099
S20.184
S-S
Na-S
0.205
0.143
1
Na2S4
Na2S6
Na2S8
1.099
1.509
1.919
Figure S1. Scanning electron microscopy (SEM) image of an as-prepared carbon nanofiber
(CNF) paper electrode (before activation).
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Figure S2. Brunauer–Emmett–Teller (BET) surface area and pore volume of the un-activated
versus CO2-activated carbon nanofiber (CNF) paper electrodes.
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Figure S3. (a) Schematic of the formation of Na2S/AC-CNF cathode. (b) Picture of an
activated CNF paper electrode.
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Figure S4. Electrochemical impedance spectroscopy (EIS) data of a sodiated Nafion
membrane in a symmetric electrochemical cell with two blocking stainless steel electrodes.
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Figure S5. Typical charge/discharge profiles of a Na-S battery prepared with a traditional
sulfur-carbon cathode.
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Figure S6. Cyclic voltammogram (at a scan rate of 0.1 mV s-1) of the Na-S cell prepared with
the traditional sulfur-carbon cathode.
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Figure S7. Comparison of the practical energy density and energy cost (based on the active
materials of anode and cathode) of the Li-S and the Na ǁ sodiated Nafion – CNF coating ǁ
Na2S-CNF cells.
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Figure S8. SEM image of a (a) porous Celgard separator and (b) a Nafion membrane.
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Figure S9. (a) SEM image of a Na anode in the Na ǁ sodiated Nafion ǁ Na2S/AC-CNF cell
after 100 cycles. (b) Sodium and (c) sulfur elemental mappings of the Na anode in the Na ǁ
sodiated Nafion ǁ Na2S/AC-CNF cell after 100 cycles obtained with EDS.
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Figure S10. Photograph of a piece of cycled (after 100 cycles) Nafion membrane taken out
from the Na ǁ sodiated Nafion/AC–CNF coating ǁ Na2S/AC-CNF cell after removing the ACCNF coating.
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