Acs.nanolett. lean electrolyte

Improving Lithium−Sulfur Battery Performance under Lean
Electrolyte through Nanoscale Confinement in Soft Swellable Gels
Junzheng Chen,†
Wesley A. Henderson,†
Huilin Pan,†
Brian R. Perdue,‡
Ruiguo Cao,†
Jian Zhi Hu,†
Chuan Wan,†
Kee Sung Han,†
Karl T. Mueller,†
Ji-Guang Zhang,†
Yuyan Shao,*,†
and Jun Liu*,†
†
Joint Center for Energy Storage Research (JCESR), Pacific Northwest National Laboratory, Richland, Washington 99352, United
States
‡
Joint Center for Energy Storage Research (JCESR), Sandia National Laboratories, Albuquerque, New Mexico 87185, United States
*S Supporting Information
ABSTRACT: Li−S batteries have been extensively studied using rigid carbon as the
host for sulfur encapsulation, but improving the properties with a reduced electrolyte
amount remains a significant challenge. This is critical for achieving high energy
density. Here, we developed a soft PEO10LiTFSI polymer swellable gel as a nanoscale
reservoir to trap the polysulfides under lean electrolyte conditions. The PEO10LiTFSI
gel immobilizes the electrolyte and confines polysulfides within the ion conducting
phase. The Li−S cell with a much lower electrolyte to sulfur ratio (E/S) of 4 gE/gS
(3.3 mLE/gS) could deliver a capacity of 1200 mA h/g, 4.6 mA h/cm2
, and good cycle
life. The accumulation of polysulfide reduction products, such as Li2S, on the cathode,
is identified as the potential mechanism for capacity fading under lean electrolyte
conditions.
KEYWORDS: Li−S battery, lean electrolyte, high energy cell, gel capture, failure mechanism
Li−S batteries have been widely studied as next-generation
energy storage technology since sulfur has a high
theoretical capacity (1672 mA h/g), low cost, and high earth
abundance.1,2
However, before the broad commercialization of
Li−S batteries, several technical challenges have to be
addressed, including Li metal anode degradation,3,4
polysulfide
dissolution,5,6
and electrolyte decomposition.7−9
The Li−S
reaction involves the dissolution of reaction intermediate
lithium polysulfides (Li2Sn) in the electrolyte which promotes
the reaction kinetics; however, the dissolution of Li2Sn also
causes the loss of active material from cathode architecture, as
well as side reactions between Li2Sn and Li metal (and possible
side reaction with electrolytes).10−12
Great progress has been
made using rigid nanostructured porous carbon or metal oxide
hosts to encapsulate the sulfur on the cathode, together with
advances in electrolyte additives and other electrode protection
strategies.13−16
The rigid encapsulation approach relies on the
interfacial binding between the substrate and the polysulfides
and charge transport across the interfaces. The majority of
investigation reported in the literature was conducted with a
high electrolyte amount. The careful analysis suggested that the
amount of electrolyte needs to be significantly reduced in order
for Li−S battery technology to achieve the desired high energy
density.17,18
Currently, most studies use a high electrolyte
amount with an electrolyte to sulfur (E/S) ratio in the range of
10−50 mLE/gS (flooded electrolyte condition).19,20
There have
been very few reports on rechargeable Li−S batteries using a
low electrolyte amount with an E/S ratio less than 5 mLE/gS
(lean electrolyte condition).18,21
It is increasingly recognized
now that good electrochemical performance obtained with
flooded electrolytes cannot be reproduced under lean electro-
lyte conditions.22−25
Quan et al. reported an E/S ratio at 3.5
mLE/gS operation under high sulfur loading, but the cell only
lasts for 10 cycles. The change to lean electrolyte condition is
critical for high pack-level energy density but places severe
restrictions on wetting, charge transport between the interface,
and electrochemical reaction kinetics. In addition, when a Li−S
cell operates under a lean electrolyte condition, its charge/
discharge behavior, cell failure model, and so forth may be
substantially different from those with flood electrolyte (i.e.,
with large E/S ratio) as we have always been doing. Certainly,
to gain good fundamental understanding, one has to be able to
run a Li−S cell for extended cycles under lean electrolyte
conditions.
In this paper, we demonstrate a soft PEO10LiTFSI polymer
gel as a nanoscale reservoir to trap the polysulfides under lean
electrolyte conditions.26−28
In this approach, the electrolyte and
the polysulfides are confined in the swellable, flexible polymer
phase which by itself is also ion conducting, thus provides more
efficient encapsulation and better ion transport properties.
Poly(ethylene oxide) (PEO) has been widely considered as a
polymer electrolyte (mixed with lithium salts) for batteries
Received: January 30, 2017
Revised: April 10, 2017
Published: April 27, 2017
Letter
pubs.acs.org/NanoLett
© 2017 American Chemical Society 3061 DOI: 10.1021/acs.nanolett.7b00417
Nano Lett. 2017, 17, 3061−3067

because it has a strong Li+
solvating ability.29−31
Several groups
also reported PEO as a binder material for Li−S systems.32−35
However, pure PEO tends to crystallize after solvent
evaporation, limiting its binding ability and practical application
in sulfur cathodes.36
Here, we use a combination of PEO and
LiTFSI to form a swelled amorphous gel-like polymer
nanocoating film on conductive carbon. Compared to rigid
high surface area carbon, this preformed PEO-LiTFSI gel
functions as a soft media for Li-ion conducting, electrolyte
wetting, and serves as a swellable reservior for retaining the
electrolyte and polysulfides near the conducting carbon
surfaces, thus enable extended cycling of lean electrolyte Li−
S cells. This study also provides a new insight of potential
degradation mechanism under lean electrolyte conditions that
are different from those under flooded electrolyte conditions.
Demonstration of Nanoscale Confinement with Soft
Swellable Gels for the Lean Electrolyte Li−S Operation.
First, we demonstrate that the PEO10LiTFSI soft gel as
swellable reservoir has excellent capability to solvate and retain
the electrolyte in the mixture. Figure 1a shows the swelling and
electrolyte uptake tests of different binders with the commonly
used 1 M LiTFSI/DME-DOL with the E/S ratio = 4 gE/gS (3.3
mLE/gS) The PEO10LiTFSI is well-swelled in the electrolytes
and absorbs 10 mL/g electrolyte within the gel layer phase.
There is no obvious interaction with other binders: poly-
(vinylidene fluoride) (PVDF), sodium carboxymethyl cellulose
(CMC), and LA133. The electrolyte retention is further
demonstrated by evaporation ratio test. The evaporation of
adsorbed electrolyte is shown in Figure 1b. Due to its low
boiling point, the electrolyte in traditional binders quickly
evaporates. However, the electrolyte evaporation loss in
PEO10LITFSI is significantly lower (<15%), which means a
good capture of the electrolyte. We believe that the key
characteristic of the PEO/LiTFSI gel is its ability to maintain an
amorphous state for an EO/Li ratio between 6 and 10 (a
phenomenon called “crystalline gap”).37,38
This crystalline gap
is formed mainly because the nucleation and growth of ordered
crystalline phases is slowed or inhibited when there is no
favorable way to pack the solvated PEO with LiTFSI solvates
together under this given concentration (PEO10LiTFSI in this
case).39
The XRD patterns of PEO before and after adding
LiTFSI confirmed this (Figure 1c). The crystalline phase of
pure PEO reflected two characteristic diffraction peaks at 20°
and 25°. After adding LiTFSI, the strong interaction between
PEO and LiTFSI resulted in a broadened peak around 20°,
suggesting that the crystalline structure of LiTFSI and PEO
disappeared. The TEM images also confirms a good nano-
coating layer of the PEO10LiTFSI on the host surface with
amorphous structure (Figure S1). The coating thickness is
around 20 nm. After it is swelled, the coating thickness is
expected to be around 100 nm based on the swelling test, and
this thin gel layer retains a good ion transfer property. It also
improves the wettability of the electrodes.
In traditional Li−S cells, the abundant electrolyte facilitates
continuous polysulfide dissolution and causes the loss of active
materials from the sulfur cathode and collapse of the host
scaffold. PEO has a similar chemical structure with DME; the
ether group would retain the dissolved polysulfides within the
swelled gel. To prove that, PEO10LITFSI was added into a
mixed solution of 18 mM Li2S8 + 1 M LiTFSI/DME + DOL
electrolyte. It needs to point out that, due to an ultra high
molecular weight of PEO we used, the dissolution of the PEO
into the electrolyte is significantly suppressed. After the phase
separation was completed, distinct color changes between the
liquid phase on the top and the swelled PEO gel electrolyte in
the bottom (Figure 1d, inset) indicates the selective confine-
ment of polysulfides within the swelled PEO10LiTFSI. The
UV−vis spectrum of the standard 18 mM Li2S8 solution and
liquid phase on top was shown in Figure 1d. The polysulfide
concentration was greatly decreased from 18 mM to ∼2 mM in
the liquid phase after it is mixed with PEO10LiTFSI.40,41
This
means a gel on the carbon host surface can selectively dissolve
Figure 1. (a) Up: solid binder powder before adding the electrolyte, bottom: swelling and electrolyte uptake test of binders in the 1 M LiTFIS
DME/DOL electrolyte. 1-PEO10LiTFSI, 2-LA133, 3-CMC, 4-PVDF. PEO10LiTFSI swelled more than 4 times in volume and uptaked ∼10 mL
electrolyte/g PEO10LiTFSI. (b) Solvent evaporation test of the electrolyte infiltrated in different binders showing a strong absorption ability of PEO
based gel capture mediate; (c) XRD patterns of PEO10LiTFSI composite before and after adding LiTFSI indicating an amorphous region due to the
interaction of Li+
with the ether group; (d) UV−vis spectra of 18 mM Li2S8 swelled in the PEO electrolyte and the polysulfide concentration changes
from 18 mM to ∼2 mM after resting for 12 h; (e) 13
C solid-state NMR spectra of PEO based composite before and after adding LiTFSI and Li2S8,
showing CH2 chain peak narrowing, indicating an increased carbon main chain flexibility due to the interaction of Li+
with ether group; (f) schematic
diagram of the electrode with PEO10LiTFSI nanofilm coating and the confinement of polysulfides by the swelled PEO10LiTFSI gel.
Nano Letters Letter
DOI: 10.1021/acs.nanolett.7b00417
Nano Lett. 2017, 17, 3061−3067
3062

more polysulfides species. During the swelling process, the
working electrolyte itself can be well-restricted within the gel
coating surface. Dipole moments and dielectric constants
increase with the increase in ethylene oxide chain length, and
PEO represents a longer chain glyme so that a higher Li+
solvation ability than DME is achieved after it was swelled with
DOL/DME blends.42,43
This leads to the strong interaction
between Li2Sx and the swelled LiTFSI/PEO gel matrix.44
In
addition, the solid state 13
C NMR spectrum of PEO10LiTFSI
before and after adding saturated Li2S8 polysulfide in the
electrolyte was used to better understand the polysulfide
interaction in the gel phase (Figure 1e). The crystalline phase
of pure PEO reflected a broad CH2 resonance peak, due to the
poor mobility of the polymer chain, and the amorphous
PEO10LiTFSI exhibits narrower sharp peaks.45
After adding the
polysulfide, the PEO10LiTFSI maintained amorphous as seen
from the unchanged narrow CH2 resonance peaks. Based on
the above discussion, the role of the new PEO10LiTFSI gel is
illustrated in Figure 1f. The swelled PEO10LiTFSI on the
cathode surface forms a Li+
-ion conducting gel network across
the whole sulfur cathode, and the gel surrounds S/CNT which
interacts with the polysulfides and confined the electrolyte and
polysulfides within the gel. Because of the good wetting
properties of PEO toward CNT, a uniform nanocoating of the
PEO10LiTFSI would be achieved which facilitates the charge
transfer at the interfaces.
The sulfur composite electrode was made by mixing 80 wt %
S-CNT composite powder, 10% super P carbon additive, and
10% PEO10LiTFSI (dry weight) to form a slurry in acetonitrile
and coated onto an Al current collector in a dry room. The
amorphous PEO10LiTFSI also functions as a good binder and
protective layer to enable a thick, uniform coating of the
cathode materials with a high sulfur loading (4−7 mg/cm2
,
Figure S2).
The electrochemical behavior of PEO10LiTFSI bound sulfur
cathode was evaluated in coin cells. The electrodes bound with
LA133/SBR binder(∼4 mg/cm2
sulfur loading) was also tested
for comparison. Under a flooded electrolyte condition (i.e.,
with excessive electrolyte), two typical discharge/charge
plateaus occur for all electrodes (Figure 2a, d). The one at
2.35 V corresponds to the transformation from elemental sulfur
to long-chain polysulfides; the other one at 2.05 V is due to the
further reduction of polysulfides to Li2S.46
The two cells with
LA133/SBR and PEO10LiTFSI nano coating cathode delivered
specific capacities of 900 mA h/g and 1208 mA h/g,
respectively, at E/S = 17 gE/gS (14.2 mLE/gS). Previously,
our group has reported in a flooded cell, the large amount of
the electrolyte can accelerate the polysulfide dissolution loss
from the cathode and resulted in a characteristic initial quick
capacity fades at first 10 cycles.23,47−49
However, the cell using
LA133/SBR binder shows a significant polarization when the
E/S ratio is reduced from 17 gE/gS to 6.8 gE/gS (5.6 mLE/gS),
especially in the second discharge plateau (Figure 2d). Under
E/S = 6.8 gE/gS condition, the cell initially showed only 580
mA h/g specific capacity and larger than 300 mV overpotential
in comparison with that using PEO10LiTFSI gel. In addition, a
further decrease of the E/S ratio to 4 gE/gS led to an even
poorer kinetics of polysulfides and delivered only a 120 mA h/g
capacity. However, the PEO10LiTFSI cell still functions well
without noticeable polarization under E/S = 4 gE/gS (3.3 mLE/
gS) and delivers an initial capacity of 1183 mA h/g (Figure 2b).
The Li−S cell also shows good cycling stability under various
E/S ratios. The capacity retention after 100 cycles under E/S =
4 gE/gS is 87.3%.
The electrochemical impedance spectra (EIS) (Figure 2c, f)
reveal that not only internal resistance but also the charge
transfer resistance is greatly reduced in PEO10LiTFSI cell in
comparison with the LA133/SBR binder cell. PEO not only
provides a pathway for the electrolyte to penetrate into the
thick cathode but also serves as an electrolyte/lithium ion
reservoir within the cathode architecture. As a result, the active
materials are well-connected with each other by highly
conductive swelled gel electrolyte.
Figure 2. (a, d) Charge−discharge curves of Li−S coin cells with PEO10LiTFSI or LA133 binder in coin cell level, (b, e) the cycling performance of
Li−S coin cell with PEO10LiTFSI or LA133 binder under different electrolyte amounts. (c, f) electrochemical impedance spectra of Li−S coin cells
with different binders under different electrolyte amount conditions.
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Nano Lett. 2017, 17, 3061−3067
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To further prove the effect on the cycling stability of the
electrolyte reservoir nanocoating, the electrodes with
PEO10LiTFSI gel and LA133 binder before and after 100
cycles under the E/S ratio = 6.8 gE/gS were characterized with
SEM (Figure 3). After cycles, both of the electrodes were
attached on the Al collector. The total thickness of the cathodes
remained stable at 125 um after 100 cycles for PEO10LiTFSI
based electrode, comparing to decreased thickness and rough
morphology of LA133 based electrode. This is consistent with
the speculation that the swelled PEO10LiTFSI within the
cathode scaffold would capture the electrolyte and dissolved
intermediates, then further stabilize the cathode.
Failure Mechanism of Li−S Pouch Cells under a Lean
Electrolyte Condition. In the literature, the dissolution of
polysulfides from cathode and failure of lithium anode was
assigned as the main failure mechanisms of reported Li−S
battery under the flooded electrolyte condition.50
As we
discussed above, in our system, polysulfides are well-confined
within cathode architecture. Our post-test analysis also
indicates Li metal still functioned very well (see Supporting
Information, Figure S3 for detailed discussion). Here, we focus
on the cell failure mechanisms as it seems to be one of the
biggest obstacles for practical rechargeable Li−S batteries. It
should be noted that, in our pouch cell, the anode/cathode
ratio and other parameters still need to be optimized, which is
well-known to affect the pouch cell performance. The cycling
performances of corresponding single layer pouch cell used for
NMR tests were shown in Figure S4. We could expect a further
decrease of E/S ratio in a multilayer pouch cell. The baseline is
set to the E/S ratio = 8 gE/gS (6.7 mLE/gS), and the lean
condition is set to E/S = 3 gE/gS(2.5 mLE/gS). Under this
condition, the cell is stably cycled at the initial 25 cycles, and
there is a quick fading afterward, comparing to a stable cycling
for 40 cycles at E/S = 8 gE/gS. To understand the degradation
mode under lean electrolyte conditions, solid-state 6
Li MAS
NMR techniques were used to characterize the cathode from
the cycled pouch cells (at charged state) (Figure 4a); the
cathode was vacuum-dried without solvent washing. There are
two main peaks at 2.4 ppm (Li2S) and −1.2 ppm (LiTFSI),
with a wide peak in-between.51
With the increase in E/S ratio,
the intensity of 6
Li peak at −1.2 ppm of the cathode increases
linearly, due to the residual electrolyte left inside the cathode
architecture. In contrast, the intensity of 2.4 ppm Li2S peak is 7
times higher under the lean condition than the flooded cell
(Supporting Information, Table S1 for detailed discussion).
This indicates that Li2S accumulated in the sulfur cathode after
cycling. The XRD patterns after different cycles further
confirms the Li2S accumulation under the lean electrolyte
conditionan increased Li2S characteristic peak after 30 cycles
comparing to the one after 10 cycles (Figure 4b). Under a lean
electrolyte condition, Li2S accumulation at the electrode is
potentially a huddle for long cycle life since it could lead to
electrode passivation and polarization after an extended cycle
life. EIS results with a different cycle number under the lean
condition were recorded and shown in Figure 4c. After cycles,
an additional semicircle at low-frequency region appeared
which could be attributed to the growth of the passivating layer
on the surface of the electrode.52−55
Under a lean electrolyte
condition, the consumption of the electrolyte and Li2S growth
at the electrode was critical according to the continuous
increase of both semicircles in the impedance spectrum, which
Figure 3. Cross-section SEM image of PEO10LiTFSI bounded
cathodes (a, b) and LA133 binder cathode (c, d) before and after
100 cycles at an E/S ratio = 6.8 gE/gS.
Figure 4. (a) 6
Li MAS NMR spectra of the cathodes after 30 cycles collected from Li−S pouch cell using a different amount of the electrolyte,
indicating a serious Li2S accumulation under the lean condition comparing to the flooded cell; (b) XRD spectrum of cycled cathode under a lean
condition with different cycling numbers, indicating the accumulation of Li2S with cycling. (c) AC impedance spectrum of Li−S single layer pouch
cell with different cycles under a E/S = 3 gE/gS lean condition.
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could lead to a serious polarization after an extended cycle life.
Future work should consider approaches to improve the
rechargeability and reversibility of Li2S through the control of
Li2S solubility and catalyzing the charge process using redox
mediators or additives.56−58
Conclusion. In summary, we report a soft gel encapsulation
approach for rechargeable Li−S cell under lean electrolyte
conditions. The swellable PEO10LiTFSI soft gel provides strong
binding ability within the cathode scaffold, absorbs electrolyte,
and forms a highly efficient Li+
conducting gel network within
the cathode. At the same time, the high polysulfide solubility in
the gel enables good polysulfides confinement, so that the
cycling stability can be improved under a lean electrolyte
condition. The Li−S cell with a much lower electrolyte to sulfur
ratio (E/S) of 4 gE/gS could deliver a capacity of 1200 mA h/g,
4.6 mA h/cm2
, and good cycle life. The mechanism study
points to the passivation of the cathode which needs more
undeetsanding in the future.
Experimental Section. Material Synthesis and Charac-
terization. The procedure to prepare S-coated MWCNTs (S-
CNT) has been previously reported.47,59
Elemental sulfur (S8,
Alfa Aesar) and the MWCNTs (Cheap Tubes Inc.) (80:20 w/
w) were mixed together by mechanical ball milling for 2 h. The
mixture was then sealed in a PTFE container and heated to 155
°C in an oven for 24 h under the protection of inert Ar gas.
Morphology observations were performed with a dual-FIB
scanning electron microscope (SEM) (FEI Helios). The solid
state 13
C NMR spectra for the polymers were obtained from
Fourier transformed free induction decays after a single pulse
excitation at Larmor frequencies of 233.2 and 81.4 MHz,
respectively, at ambient temperature (∼25 °C) using a 600
MHz NMR spectrometer (Agilent, USA). The 13
C chemical
shifts for TMS were used as an external reference (i.e., 0 ppm).
6
Li MAS NMR experiments for post cycled pouch cathodes
were performed at 20 °C on a Varian-Inova 850 MHz NMR
spectrometer, operating at a magnetic field of 19.975 T. The 6
Li
MAS spectra were acquired at 125.050 MHz using a single π/4
pulse sequence with a pulse width of 2 μs and a recycle delay at
10 s. A 4 mm pencil type MAS rotor at a sample spinning rate
of 10 kHz were used. 6
Li chemical shifts were externally
referenced to 1 M LiCl aqueous solution (i.e., 0 ppm). All of
the samples were collected from a single layer pouch cell and
packed into an airtight MAS rotor in an argon-filled glovebox.
The ionic conductivity of the electrolytes was measured by a
conductivity meter (Orion 3 Star, Thermo Scientific) 3 times.
The UV−vis spectrum was conducted in the Shimadzu UV−vis
3600 at room temperature using the 1 M LiTFSI and 0.2 M
LiNO3 dissolved in a mixture of 1,3-dioxolane (DOL) and 1,2-
dimethoxyethane (DME) (1:1 v/v) electrolyte as the baseline.
Electrochemical Test. PEO (Sigma-Aldrich, Mw =
4,000,000) was dried under vacuum at 120 °C for 5 days
before use. PEO10LiTFSI was prepared by mixing 40 wt %
LiTFSI and 60 wt % PEO in acetonitrile and stirred at 60 °C
for 24 h. This forms a molar ratio of EO/Li = 10. The
PEO10LiTFSI based cathode with ca. 4 mg-S cm−2
loading was
prepared by mixing 80 wt % S-CNT composite powder, 10%
super P carbon additive, and 10% PEO10LiTFSI in acetonitrile
under the dry atmosphere to form a cathode slurry. Then the
slurry was coated on a carbon coated aluminum collector (MTI
Corp.) and baked at 60 °C under vacuum overnight. The dry
electrode thickness is well-controlled to 120 um at 4 mg/cm2
sulfur loading, and the porosity of the cathode is optimized to
65−70%. The LA133/SBR reference cathode with ca. 4 mg-S
cm−2
loading was prepared similarly by mixing 80 wt % S-CNT
composite powder, 10% super P carbon additive, 5 wt % LA133
binder (Chengdu Indigo Co.), and 5 wt % SBR binder (MTI
Corp.) and forming a slurry with water. The slurries were also
coated onto a C-coated Al foil current collector. Electrodes
were punched to a 1.6 mm2
diameter size. The electrolytes used
were 1 M LiTFSI and 0.2 M LiNO3 dissolved in a mixture of
1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) (1/1
v/v), respectively. Half cells with 200 μm thick Li metal foil as
the anode and Celgard 3501 as the separator were assembled
using CR2032 coin cells in an argon-filled glovebox. The
galvanostatic discharge/charge cycles were tested using a
LANHE battery tester at 300 K in a voltage cutoff protocol
between 2.7 and 1.8 V. The specific capacity (SC) was based on
the sulfur mass in the C/S composites, and the areal capacity
(AC) was calculated by the equation AC = SC × areal sulfur
loading. AC impedance was measured using the Solartron
electrochemical workstation. The AC amplitude was ±15 mV,
and the applied frequency range was from 100 kHz to 0.1 Hz.
■ ASSOCIATED CONTENT
*S Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.nano-
lett.7b00417.
(PDF)
■ AUTHOR INFORMATION
Corresponding Authors
*E-mail: jun.liu@pnnl.gov.
*E-mail: yuyan.shao@pnnl.gov.
ORCID
Jian Zhi Hu: 0000-0001-8879-747X
Karl T. Mueller: 0000-0001-9609-9516
Ji-Guang Zhang: 0000-0001-7343-4609
Jun Liu: 0000-0001-8663-7771
Present Address
J.C.: 24 M Technologies, Inc., Cambridge, MA 02139, United
States.
Notes
The authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
This work was supported as part of the Joint Center for Energy
Storage Research (JCESR), an Energy Innovation Hub funded
by the U.S. Department of Energy (DOE), Office of Science,
Basic Energy Sciences (BES). The NMR spectroscopy and
SEM were performed in the Environmental Molecular Sciences
Laboratory (EMSL), a national scientific user facility sponsored
by the U.S. Department of Energy’s Office of Biological and
Environmental Research and located at Pacific Northwest
National Laboratory (PNNL). We gratefully acknowledge Dr.
Kevin R. Zavadil and Dr. Kevin G. Gallagher for helpful
discussions.
■ REFERENCES
(1) Manthiram, A.; Fu, Y.; Chung, S. H.; Zu, C.; Su, Y. S.
Rechargeable lithium-sulfur batteries. Chem. Rev. 2014, 114 (23),
11751−11787.
(2) Pang, Q.; Liang, X.; Kwok, C. Y.; Nazar, L. F. Review-The
Importance of Chemical Interactions between Sulfur Host Materials
Nano Letters Letter
Nano Lett. 2017, 17, 3061−3067
3065

and Lithium Polysulfides for Advanced Lithium-Sulfur Batteries. J.
Electrochem. Soc. 2015, 162 (14), A2567−A2576.
(3) Tu, Z. Y.; Nath, P.; Lu, Y. Y.; Tikekar, M. D.; Archer, L. A.
Nanostructured Electrolytes for Stable Lithium Electrodeposition in
Secondary Batteries. Acc. Chem. Res. 2015, 48 (11), 2947−2956.
(4) Cao, R.; Xu, W.; Lv, D.; Xiao, J.; Zhang, J.-G. Anodes for
Rechargeable Lithium-Sulfur Batteries. Adv. Energy Mater. 2015, 5
(16), 1402273.
(5) Luo, C.; Zhu, Y. J.; Borodin, O.; Gao, T.; Fan, X. L.; Xu, Y. H.;
Xu, K.; Wang, C. S. Activation of Oxygen-Stabilized Sulfur for Li and
Na Batteries. Adv. Funct. Mater. 2016, 26 (5), 745−752.
(6) Ma, L.; Zhuang, H. L. L.; Wei, S. Y.; Hendrickson, K. E.; Kim, M.
S.; Cohn, G.; Hennig, R. G.; Archer, L. A. Enhanced Li-S Batteries
Using Amine-Functionalized Carbon Nanotubes in the Cathode. ACS
Nano 2016, 10 (1), 1050−1059.
(7) Zhang, S.; Ueno, K.; Dokko, K.; Watanabe, M. Recent Advances
in Electrolytes for Lithium-Sulfur Batteries. Adv. Energy Mater. 2015, 5
(16), 1500117.
(8) Jin, Z. Q.; Xie, K.; Hong, X. B. Review of Electrolyte for Lithium
Sulfur Battery. Huaxue Xuebao 2014, 72 (1), 11−20.
(9) Chen, J.; Han, K. S.; Henderson, W. A.; Lau, K. C.; Vijayakumar,
M.; Dzwiniel, T.; Pan, H.; Curtiss, L. A.; Xiao, J.; Mueller, K. T.; Shao,
Y.; Liu, J. Restricting the Solubility of Polysulfides in Li-S Batteries Via
Electrolyte Salt Selection. Adv. Energy Mater. 2016, 6 (11), 1600160.
(10) Kamphaus, E. P.; Balbuena, P. B. Long-Chain Polysulfide
Retention at the Cathode of Li-S Batteries. J. Phys. Chem. C 2016, 120
(8), 4296−4305.
(11) Diao, Y.; Xie, K.; Xiong, S. Z.; Hong, X. B. Insights into Li-S
Battery Cathode Capacity Fading Mechanisms: Irreversible Oxidation
of Active Mass during Cycling. J. Electrochem. Soc. 2012, 159 (11),
A1816−A1821.
(12) Xu, R.; Belharouak, I.; Zhang, X. F.; Chamoun, R.; Yu, C.; Ren,
Y.; Nie, A. M.; Shahbazian-Yassar, R.; Lu, J.; Li, J. C. M.; Amine, K.
Insight into Sulfur Reactions in Li-S Batteries. ACS Appl. Mater.
Interfaces 2014, 6 (24), 21938−21945.
(13) Hwang, J.-Y.; Kim, H. M.; Lee, S.-K.; Lee, J.-H.; Abouimrane, A.;
Khaleel, M. A.; Belharouak, I.; Manthiram, A.; Sun, Y.-K. High-Energy,
High-Rate, Lithium−Sulfur Batteries: Synergetic Effect of Hollow
TiO2-Webbed Carbon Nanotubes and a Dual Functional Carbon-
Paper Interlayer. Adv. Energy Mater. 2016, 6 (1), 1501480.
(14) Lee, S. K.; Oh, S. M.; Park, E.; Scrosati, B.; Hassoun, J.; Park, M.
S.; Kim, Y. J.; Kim, H.; Belharouak, I.; Sun, Y. K. Highly Cyclable
Lithium-Sulfur Batteries with a Dual-Type Sulfur Cathode and a
Lithiated Si/SiOx Nanosphere Anode. Nano Lett. 2015, 15 (5), 2863−
2868.
(15) Xu, Y. H.; Wen, Y.; Zhu, Y. J.; Gaskell, K.; Cychosz, K. A.;
Eichhorn, B.; Xu, K.; Wang, C. S. Confined Sulfur in Microporous
Carbon Renders Superior Cycling Stability in Li/S Batteries. Adv.
Funct. Mater. 2015, 25 (27), 4312−4320.
(16) Hu, H.; Cheng, H. Y.; Liu, Z. F.; Li, G. J.; Zhu, Q. C.; Yu, Y. In
Situ Polymerized PAN-Assisted S/C Nanosphere with Enhanced
High-Power Performance as Cathode for Lithium/Sulfur Batteries.
Nano Lett. 2015, 15 (8), 5116−5123.
(17) Eroglu, D.; Zavadil, K. R.; Gallagher, K. G. Critical Link between
Materials Chemistry and Cell-Level Design for High Energy Density
and Low Cost Lithium-Sulfur Transportation Battery. J. Electrochem.
Soc. 2015, 162 (6), A982−A990.
(18) Hagen, M.; Hanselmann, D.; Ahlbrecht, K.; Maça, R.; Gerber,
D.; Tübke, J. Lithium−Sulfur Cells: The Gap between the State-of-the-
Art and the Requirements for High Energy Battery Cells. Adv. Energy
Mater. 2015, 5 (16), 1401986.
(19) Hagen, M.; Fanz, P.; Tubke, J. Cell energy density and
electrolyte/sulfur ratio in Li-S cells. J. Power Sources 2014, 264, 30−34.
(20) Kang, S. H.; Zhao, X.; Manuel, J.; Ahn, H. J.; Kim, K. W.; Cho,
K. K.; Ahn, J. H. Effect of sulfur loading on energy density of lithium
sulfur batteries. Phys. Status Solidi A 2014, 211 (8), 1895−1899.
(21) Urbonaite, S.; Poux, T.; Novák, P. Progress Towards
Commercially Viable Li−S Battery Cells. Adv. Energy Mater. 2015, 5
(16), 1500118.
(22) Zhang, S. S. New insight into liquid electrolyte of rechargeable
lithium/sulfur battery. Electrochim. Acta 2013, 97, 226−230.
(23) Zhang, S. S. Improved Cyclability of Liquid Electrolyte Lithium/
Sulfur Batteries by Optimizing Electrolyte/Sulfur Ratio. Energies 2012,
5 (12), 5190−5197.
(24) Urbonaite, S.; Novak, P. Importance of ’unimportant’
experimental parameters in Li-S battery development. J. Power Sources
2014, 249, 497−502.
(25) Zheng, J. M.; Lv, D. P.; Gu, M.; Wang, C. M.; Zhang, J. G.; Liu,
J.; Xiao, J. How to Obtain Reproducible Results for Lithium Sulfur
Batteries? J. Electrochem. Soc. 2013, 160 (11), A2288−A2292.
(26) Qie, L.; Manthiram, A. A Facile Layer-by-Layer Approach for
High-Areal-Capacity Sulfur Cathodes. Adv. Mater. 2015, 27 (10),
1694−1700.
(27) Qie, L.; Manthiram, A. High-Energy-Density Lithium−Sulfur
Batteries Based on Blade-Cast Pure Sulfur Electrodes. ACS Energy Lett.
2016, 1 (1), 46−51.
(28) Hu, G. J.; Xu, C.; Sun, Z. H.; Wang, S. G.; Cheng, H. M.; Li, F.;
Ren, W. C. 3D Graphene-Foam-Reduced-Graphene-Oxide Hybrid
Nested Hierarchical Networks for High-Performance Li-S Batteries.
Adv. Mater. 2016, 28 (8), 1603−1609.
(29) Mao, G.; Saboungi, M.-L.; Price, D. L.; Armand, M. B.; Howells,
W. S. Structure of Liquid PEO-LiTFSI Electrolyte. Phys. Rev. Lett.
2000, 84 (24), 5536−5539.
(30) MacGlashan, G. S.; Andreev, Y. G.; Bruce, P. G. Structure of the
polymer electrolyte poly(ethylene oxide)6:LiAsF6. Nature 1999, 398
(6730), 792−794.
(31) Lightfoot, P.; Mehta, M. A.; Bruce, P. G. Crystal Structure of the
Polymer Electrolyte Poly(ethylene oxide)3:LiCF3SO3. Science 1993,
262 (5135), 883.
(32) Zhang, S. S. A Concept for Making Poly(ethylene oxide) Based
Composite Gel Polymer Electrolyte Lithium/Sulfur Battery. J.
Electrochem. Soc. 2013, 160 (9), A1421−A1424.
(33) Zhang, S. S. Liquid electrolyte lithium/sulfur battery:
Fundamental chemistry, problems, and solutions. J. Power Sources
2013, 231, 153−162.
(34) Jeong, S. S.; Lim, Y.; Choi, Y. J.; Cho, G. B.; Kim, K. W.; Ahn,
H. J.; Cho, K. K. Electrochemical properties of lithium sulfur cells
using PEO polymer electrolytes prepared under three different mixing
conditions. J. Power Sources 2007, 174 (2), 745−750.
(35) Li, Y. J.; Zhan, H.; Huang, K. L.; Zhou, Y. H. All Solid State
Lithium Sulfur Rechargeable Battery with PEO-based Polymer
Electrolytes. Acta Chim. Sinica 2010, 68 (18), 1850−1854.
(36) Lacey, M. J.; Jeschull, F.; Edstrom, K.; Brandell, D. Functional,
water-soluble binders for improved capacity and stability of lithium-
sulfur batteries. J. Power Sources 2014, 264, 8−14.
(37) Henderson, W. A. Crystallization Kinetics of Glyme−LiX and
PEO−LiX Polymer Electrolytes. Macromolecules 2007, 40 (14), 4963−
4971.
(38) Lascaud, S.; Perrier, M.; Vallee, A.; Besner, S.; Prud’homme, J.;
Armand, M. Phase Diagrams and Conductivity Behavior of Poly-
(ethylene oxide)-Molten Salt Rubbery Electrolytes. Macromolecules
1994, 27 (25), 7469−7477.
(39) Han, S.-D.; Borodin, O.; Seo, D. M.; Zhou, Z.-B.; Henderson,
W. A. Electrolyte Solvation and Ionic Association: V. Acetonitrile-
Lithium Bis(fluorosulfonyl)imide (LiFSI) Mixtures. J. Electrochem. Soc.
2014, 161 (14), A2042−A2053.
(40) Patel, M. U.; Dominko, R. Application of In Operando UV/Vis
Spectroscopy in Lithium-Sulfur Batteries. ChemSusChem 2014, 7 (8),
2167−2175.
(41) Patel, M. U. M.; Demir-Cakan, R.; Morcrette, M.; Tarascon, J.
M.; Gaberscek, M.; Dominko, R. Li-S Battery Analyzed by UV/Vis in
Operando Mode. ChemSusChem 2013, 6 (7), 1177−1181.
(42) Yoshida, K.; Tsuchiya, M.; Tachikawa, N.; Dokko, K.;
Watanabe, M. Change from Glyme Solutions to Quasi-ionic Liquids
for Binary Mixtures Consisting of Lithium Bis-
(trifluoromethanesulfonyl)amide and Glymes. J. Phys. Chem. C 2011,
115 (37), 18384−18394.
Nano Letters Letter
Nano Lett. 2017, 17, 3061−3067
3066

(43) Tang, S.; Zhao, H. Glymes as versatile solvents for chemical
reactions and processes: from the laboratory to industry. RSC Adv.
2014, 4 (22), 11251−11287.
(44) Fan, F. Y.; Pan, M. S.; Lau, K. C.; Assary, R. S.; Woodford, W.
H.; Curtiss, L. A.; Carter, W. C.; Chiang, Y.-M. Solvent Effects on
Polysulfide Redox Kinetics and Ionic Conductivity in Lithium-Sulfur
Batteries. J. Electrochem. Soc. 2016, 163 (14), A3111−A3116.
(45) Wickham, J. R.; York, S. S.; Rocher, N. M.; Rice, C. V. Lithium
Environment in Dilute Poly(ethylene oxide)/Lithium Triflate Polymer
Electrolyte from REDOR NMR Spectroscopy. J. Phys. Chem. B 2006,
110 (10), 4538−4541.
(46) Zhou, G. M.; Li, L.; Ma, C. Q.; Wang, S. G.; Shi, Y.; Koratkar,
N.; Ren, W. C.; Li, F.; Cheng, H. M. A graphene foam electrode with
high sulfur loading for flexible and high energy Li-S batteries. Nano
Energy 2015, 11, 356−365.
(47) Chen, J. Z.; Wu, D. X.; Walter, E.; Engelhard, M.; Bhattacharya,
P.; Pan, H. L.; Shao, Y. Y.; Gao, F.; Xiao, J.; Liu, J. Molecular-
confinement of polysulfides within mesoscale electrodes for the
practical application of lithium sulfur batteries. Nano Energy 2015, 13,
267−274.
(48) Lv, D. P.; Zheng, J. M.; Li, Q. Y.; Xie, X.; Ferrara, S.; Nie, Z. M.;
Mehdi, L. B.; Browning, N. D.; Zhang, J. G.; Graff, G. L.; Liu, J.; Xiao,
J. High Energy Density Lithium-Sulfur Batteries: Challenges of Thick
Sulfur Cathodes. Adv. Energy Mater. 2015, 5 (16), 1402290.
(49) Gordin, M. L.; Dai, F.; Chen, S. R.; Xu, T.; Song, J. X.; Tang, D.
H.; Azimi, N.; Zhang, Z. C.; Wang, D. H. Bis(2,2,2-trifluoroethyl)
Ether As an Electrolyte Co-solvent for Mitigating Self-Discharge in
Lithium-Sulfur Batteries. ACS Appl. Mater. Interfaces 2014, 6 (11),
8006−8010.
(50) Rosenman, A.; Markevich, E.; Salitra, G.; Aurbach, D.; Garsuch,
A.; Chesneau, F. F. Review on Li-Sulfur Battery Systems: an Integral
Perspective. Adv. Energy Mater. 2015, 5 (16), 1500212.
(51) Xiao, J.; Hu, J. Z.; Chen, H.; Vijayakumar, M.; Zheng, J.; Pan,
H.; Walter, E. D.; Hu, M.; Deng, X.; Feng, J.; Liaw, B. Y.; Gu, M.;
Deng, Z. D.; Lu, D.; Xu, S.; Wang, C.; Liu, J. Following the Transient
Reactions in Lithium−Sulfur Batteries Using an In Situ Nuclear
Magnetic Resonance Technique. Nano Lett. 2015, 15 (5), 3309−3316.
(52) Cañas, N. A.; Hirose, K.; Pascucci, B.; Wagner, N.; Friedrich, K.
A.; Hiesgen, R. Investigations of lithium−sulfur batteries using
electrochemical impedance spectroscopy. Electrochim. Acta 2013, 97,
42−51.
(53) Fronczek, D. N.; Bessler, W. G. Insight into lithium-sulfur
batteries: Elementary kinetic modeling and impedance simulation. J.
Power Sources 2013, 244, 183−188.
(54) Kolosnitsyn, V. S.; Kuzmina, E. V.; Karaseva, E. V.; Mochalov, S.
E. A study of the electrochemical processes in lithium-sulphur cells by
impedance spectroscopy. J. Power Sources 2011, 196 (3), 1478−1482.
(55) Yuan, L. X.; Qiu, X. P.; Chen, L. Q.; Zhu, W. T. New insight
into the discharge process of sulfur cathode by electrochemical
impedance spectroscopy. J. Power Sources 2009, 189 (1), 127−132.
(56) Gerber, L. C. H.; Frischmann, P. D.; Fan, F. Y.; Doris, S. E.; Qu,
X.; Scheuermann, A. M.; Persson, K.; Chiang, Y. M.; Helms, B. A.
Three-Dimensional Growth of Li2S in Lithium-Sulfur Batteries
Promoted by a Redox Mediator. Nano Lett. 2016, 16 (1), 549−554.
(57) Meini, S.; Elazari, R.; Rosenman, A.; Garsuch, A.; Aurbach, D.
The Use of Redox Mediators for Enhancing Utilization of Li2S
Cathodes for Advanced Li-S Battery Systems. J. Phys. Chem. Lett. 2014,
5 (5), 915−918.
(58) Zheng, J.; Gu, M.; Wang, C.; Zuo, P.; Koech, P. K.; Zhang, J. G.;
Liu, J.; Xiao, J. Controlled Nucleation and Growth Process of Li2S2/
Li2S in Lithium-Sulfur Batteries. J. Electrochem. Soc. 2013, 160 (11),
A1992−A1996.
(59) Wu, F.; Chen, J.; Li, L.; Zhao, T.; Liu, Z.; Chen, R.
Polyethylene-Glycol-Doped Polypyrrole Increases the Rate Perform-
ance of the Cathode in Lithium−Sulfur Batteries. ChemSusChem 2013,
6 (8), 1438−1444.
Nano Letters Letter
Nano Lett. 2017, 17, 3061−3067
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