Bildiriler Kitabı
TMMOB Metalurji ve Malzeme Mühendisleri Odası
The Use of Polysulfide Barriers to Improve the Performance
of Room-Temperature Sodium-Sulfur (Na-S) Batteries
Abstract
Limited resources of lithium paves a way to
extensive research of room temperature sodiumsulfur batteries with the reason of being earthabundant nature and cheapness of sodium element.
However, LWIDFHV³6KXWWOH(IIHFW´as seen in lithiumsulfur batteries. To suppress this effect, an ion
selective membrane was inserted between the
separators located among cathode and anode. It is
expected that this design would entrap soluble
polysulfides on the cathode side and suppress the
shuttle effect.
1.
Introduction
Lithium-Sulfur (Li-S) batteries are one of the most
promising type among lithium-based batteries with
high theoretical capacity (1672 mAh/g) and energy
density (2600 Wh/kg). However limited resource of
lithium makes researchers find alternative anodic
materials. Sodium is one of the most suitable anode
materials among them. By combining sulfur with
sodium at room temperature provides all advantages
of lithium-sulfur batteries besides decreasing battery
cost.
Na-S batteries have similar charge-discharge process
and same limitations with Li-S batteries which are i)
insulating nature of sulfur, (ii) dissolution of
polysulfides in electrolyte which results in loss of
active material and capacity fading, (iii) shuttle
effect of dissolved polysulfides, (iv) dendrite
formation on lithium metal anode which causes
safety problems. 1-12
Herein, in order to eliminate the poisoning of the
sodium anode from polysulfide attacks, an ion
selective membrane was used between anode and
Elif Ceylan Cengiz, Rezan Demir-Çakan
Gebze Technical University - Türkiye
cathode as barrier, Na2S5 dissolved into electrolyte
(so-called catholyte) was used as cathode while
sodium is as anode side. With this configuration, we
aim to keep dissolved polysulfides on the cathode
side and thereafter their electrochemical
performance was investigated. Firstly, different
solvent-salt combinations were tried to determine the
best performing combination for Na-S batteries
followed by determination of solvent-salt complex.
Additionally, different cut-off voltages were tried to
observe their effect on the cell performance.
2.
Experimental Procedure
2.1. Synthesis of Na2S5 Powder and Preparation
of Catholyte
Stochiometric amounts of sulfur powder and sodium
particles were dissolved into ethylene glycol diethyl
HWKHU DW ƒ& IRU VHYHUDO GD\V $IWHU GU\LQJ
procedure, catholyte was prepared as including 0.1
M Na2S5 powder in electrolytes. Catholyte was used
directly as active material.
2.2. Preparation of C/S Composite
Mesoporous Carbon/Sulfur (MCS) composite which
gave the one of the best result in Li-S batteries was
used for comparison.13 For the synthesis of
mesoporous carbon, a sacrificial SBA-15 template
was synthesized according to the method described
by Stucky et al.15. After the synthesis, the pores of
the SBA-15 template were completely filled with an
aqueous solution of sucrose/H2SO4. The resulting
wet sucrose/SBA- ZDVFDOFLQHGDWƒ&XQGHU
an inert atmosphere. The silica was thereafter
removed from the composites using a 4 M aqueous
solution of ammonium hydrogen difluoride yielding
carbon replicas. Then mesoporous carbon and sulfur
18. Uluslararası Metalurji ve Malzeme Kongresi
|
IMMC 2016
749
UCTEA Chamber of Metallurgical & Materials Engineers
2.3. Cell Assembly
Measurements
and
electrolytes (catholyte) were at cathode side. Since
Nafion has SO3- groups, the polysulfides Sn2- formed
during discharge are pushed from the membrane.
Thus, they are not able to migrate from anode side
and are kept at cathode side. According to Fig. 1, 1
M NaOTF in TEGDME gave the best
9ROWDJH9YV1D
(50/55 wt%) were placed in a crucible and mixed.
7KHPL[WXUHZDVKHDWHGWRƒ&DQGQRDGGLWLRQDO
washing procedure was applied afterward. The
carbon/sulfur composite (MCS) after impregnation
DW ƒ& KDV ZW sulfur, as proven by
thermogravimetric analysis (TGA) (data not shown).
Prior to testing, the composite was hand-milled with
20 wt% Ketjen Black carbon. Final composite
contains 40% S. For the battery in which MCS was
used as cathode, 0.2 mL bare electrolyte (1 M
NaOTF in TEGDME) is used.
Proceedings Book
Electrochemical
Classical two-electrode Swagelok-typeTM cells were
assembled in an Argon filled glove box. At first,
different solvent-salt combinations were tried. These
are 1 M NaClO4 (Sodium perchlorate) in TEGDME
(Tetra ethylene glycol dimethyl ether), 1 M
NaCF3SO3 (Sodium trifluoromethanesulfonateNaOTF) in TEGDME, 1 M NaOTF in TMS (Tetra
methylene sulfone), 1 M NaOTF in DOL:DME (1,3Dioxolane:
1,2-Dimethoxyethane).
Each
Na/dissolved polysulfide cell includes 0.1 mL of
Na2S5 containing 1 M salt in solvent and 0.1 mL bare
electrolyte. After seeing that "1 M NaOTF in
TEDGME" gave the best result, the other cells were
made with this electrolyte.
And additionally, different cut-off voltages were
used to see their effect on battery performance.
3.
Results and Discussion
Electrolytes are very important component in Li-S
battery systems, because they effect the chargedischarge mechanism substantially. Thus, herein the
performance of electrolytes were investigated at
first. Figure 1 shows the effect of electrolyte on
Na/polysulfide batteries. To do so, four different
combinations of electrolytes were prepared, these
are 1 M NaOTF salt in TEGDME, 1 M NaOTF in
TMS, 1 M NaOTF in DOL:DME, 1 M NaClO4 in
TEGDME. All of these batteries had Nafion between
the separators which were both located between
anode and cathode. While bare electrolytes were
present at the anode side, 0.1 M Na2S5 contained
750
IMMC 2016
|
01D27)LQ7(*'0(
01D27)LQ706
&DSDFLW\P$KJ
01D27)LQ'2/'0(
01D&O2LQ7(*'0(
'LVFKDUJH&DSDFLW\P$KJ
Galvanostatic
cycling
measurements
were
performed using with the C/10 current density using
a galvanostat/potentiostat VMP3. The voltage range
is between 1.2-2.8 V vs Na. The amount of catholyte
was fixed to 0.1 mL for all batteries. Nafion NR-212
membranes were used directly during battery
assembly.
01D27)'2/'0(
01D&O27(*'0(
01D27)LQ7(*'0(
01D27)LQ706
&\FOH1XPEHU
Fig. 1 Na-S cells with different electrolytes. (a)
galvanostatic charge/discharge curves (C/10), (b)
Discharge capacities as a function of the cycle
number.
result, because TEGDME which is a glyme-based
solvent can dissolve polysulfides to a large extent,
since it has high donor number and low dielectric
constant. Although DOL:DME is commonly used in
Li-S batteries, by means of showing good
performances, which did not perform well in Na-S
batteries. Moreover, polarization is lower than the
RWKHUHOHFWURO\WHVLQWKHFDVHRIXVLQJ³0NaOTF
LQ7(*'0(´HOHFWURO\WH
Conventional C/S cathode and Na/polysulfide
batteries with and without Nafion were compared.
These cells were operated between 1.2-2.8 V at C/10
current density. The capacity of the battery with
Nafion has higher capacity than conventional C/S
cathode and battery without Nafion. The reason of
the low capacity of the battery with Nafion at first
18 th International Metallurgy & Materials Congress
Bildiriler Kitabı
cycle can be because of non-wettability of Nafion.
After several cycles, capacity started to increase and
even at 40th cycle, ~300 mAh/g discharge capacity
was obtained. Thus, Nafion barrier enhances the
sulfur utilization of Na-S batteries. In addition to
these, the reduction of polarization can be clearly
seen in the case of battery with Nafion.
The end-of discharge product Na2S is the main
reason of capacity fading. Eliminating of this
product may enhance the capacity and stability of
cells. Na2S formation can be prevented by varying
the cut-off voltages. It is known that Na2S is formed
approximately 1.5 V, so if battery operates above
this voltage, i.e. 1.7 V, it is thought that Na2S
formation can be hindered. In this regard, different
cut-off voltages which are 1.2-2.2 V, 1.7-2.8 V and
1.2-2.8 V were applied to the cells. Expectedly, 1.72.8 V results the best performance.
CONCLUSION
In this work, using Nafion barrier in roomtemperature Na-S batteries was investigated. It is
obvious that confinement of sulfur into carbon pores
is not a permanent solution, so different ideas are
needed. Adding barrier to battery system is a good
option for this reason. In this article, NR-212 type
Nafion was used to prevent polysulfide shuttle and
results show that this configuration is very effective
to increase discharge capacity. In addition to this, it
was thought that tuning the cut-off voltage may
prevent the Na2S formation which is one of the
biggest problems seen in Na-S batteries.
TMMOB Metalurji ve Malzeme Mühendisleri Odası
[5] S. Wenzel, H. Metelmann, C. Raiss, A. K. Durr,
J. Janek, P. Adelhelm, J. Power Sources 2013,243,
758.
[6] I. Kim, J.Y. Park, C.H. Kim, J.W. Park, J.P. Ahn,
J.-H. Ahn, K.W. Kim, H.J. Ahn, J. Power
Sources,2016, 301, 332-337.
[7] I. Bauer, M. Kohl, H. Althues, S. Kaskel, Chem.
Commun. 2014, 50, 3208.
[8] X. W. Yu, A. Manthiram, J. Phys. Chem.
Lett. 2014, 5, 1943.
[9] X.W.Yu,A.Manthiram, ChemElectroChem 2014
, 1, 1275.
[10] X. W. Yu., A. Manthiram, J. Phys. Chem.
C 2014, 118, 22952.
[11] X. W. Yu., A. Manthiram, Adv. Energy
Mater. 2015, 1500350.
[12] X.Y. Liu, Z.Q. Shan, K.L. Zhu, J.Y. Du, Q.W.
Tang, J.H. Tian, J. Power Sources, 2015, 274 85±93.
[13] X. Ji, K. T. Lee and L. F. Nazar, Nat. Mater.,
2009, 8, 500.
ACKNOWLEDGEMENTS
This work is partially supported by National Young
Researchers Career Development Grant of
TUBITAK (contract no: 213M374).
REFERENCES
[1] C. W. Park, J. H. Ahn, H. S. Ryu, K. W. Kim, H.
J. Ahn, Electrochem. Solid St. 2006, 9, A123.
[2] D. J. Lee, J. W. Park, I. Hasa, Y. K. Sun, B.
Scrosati, J. Hassoun, J. Mater. Chem. A 2013, 1,
5256.
[3] T. H. Hwang, D. S. Jung, J. S. Kim, B. G. Kim,
J. W. Choi, Nano Lett. 2013, 13, 4532.
[4] S. Xin, Y. X. Yin, Y. G. Guo, L. J. Wan, Adv.
Mater. 2014, 26, 1261.
18. Uluslararası Metalurji ve Malzeme Kongresi
|
IMMC 2016
751