Heteroatomic Te: XS1- x molecule/C nanocomposites as stable cathode materials in carbonate-based electrolytes for lithium-chalcogen batteries

Article abstract of DOI:10.1039/c8ta02751j

A stable cathode material in a conventional carbonate-based electrolyte for high-energy lithium-chalcogen batteries was successfully fabricated by homogeneously confining heteroatomic Te_xS_1-x molecules into ordered mesoporous carbon CMK-3 via a facile melt-impregnation route. The Te-S bonds in the heteroatomic Te_xS_1-x molecules endow them with higher intrinsic electrical conductivity and electrochemical reaction activity with Li than the homoatomic S₈ molecules. Moreover, Te-containing polychalcogenide intermediates could induce the formation of solid electrolyte interphase (SEI) layers on the Te_xS_1-x/CMK-3 surfaces in the carbonate-based electrolyte, which efficiently prevent polychalcogenides from the shuttle effect and side reactions with the carbonate solvent. With further assistance of mesopore confinement of CMK-3, the Te_xS_1-x/CMK-3 composites can be reversibly charged and discharged in the carbonate-based electrolyte with long cycling stability and high rate capability. Therefore, the Te_0.1S_0.9/CMK-3 composite with an optimal Te/S mole ratio of 1/9 maintains high reversible capacities of 845 mA h g^-1 after 100 cycles at 250 mA g^-1 and 485 mA h g^-1 after 500 cycles at 1 A g^-1. These encouraging results suggest that the heteroatomic Te_xS_1-x molecule/C composite could be a promising cathode material for long cycle life and high power density lithium batteries.

Full text of DOI:10.1039/c8ta02751j

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ARTICLE
Heteroatomic Te S
molecule/C nanocomposites as stable
x 1-x
cathode materials in carbonate-based electrolytes for lithium-
chalcogen batteries
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Fugen Sun,* Bo Zhang, Hao Tang, Zhihao Yue, Xiaomin Li, Chuanqiang Yin and Lang Zhou*
www.rsc.org/
A stable cathode material in a conventional carbonate-based electrolyte for high-energy lithium-chalcogen batteries was
successfully fabricated by homogeneously confining heteroatomic Te
CMK-3 via a facile melt−impregnaꢀon route. The Te-S bonds in the heteroatomic Te
higher intrinsic electrical conductivity and electrochemical reaction activity with Li than the homoatomic S
Moreover, the Te-containing polychalcogenide intermediates could induce the formation of solid electrolyte interphase
SEI) layers on the Te 1-x/CMk-3 surfaces in the carbonate-based electrolyte, which efficiently prevent polychalcogenides
from shuttle effect and side reaction with the carbonate solvent. With further assistance of mesopore confinement of
CMK-3, the Te 1-x/CMk-3 composites can be reversibly charged and discharged in the carbonate-based electrolyte with
long cycling stability and high rate capability. Therefore, the Te0.1 0.9/CMK-3 composite with an optimal Te/S mole ratio of
x
S
1-x molecules into ordered mesoporous carbons
1-x molecules endow them with
molecules.
x
S
8
(
x
S
x
S
S
-
1
-1
-1
1
/9 maintains the high reversible capacities of 845 mAh g after 100 cycles at 250 mA g and 485 mAh g after 500 cycles
-
1
at 1 A g . These encouraging results suggest that the heteroatomic Te
x
S1-x molecule/C composite could be a promising
cathode material for the long cycle life and high power density lithium battery.
and cycling stability for efficient Li ion storage.
Introduction
From this perspective, selenium and tellurium, the other
two solid nonradioactive chalcogen element, have much
The rapidly developing market for mobile electronics and
electric vehicles (EVs) has prompted the urgent need for high
energy density and long-lasting rechargeable batteries.
Current Li-ion batteries using electrodes based on transition
metal oxides and phosphates cannot satisfy this demand in
−
higher electronic conductivity (Se: 1×10 S m ; Te: 2×10 S m
3
-1
2
-
1
)
than S and comparable theoretical volumetric capacity (Se:
[7-9]
It is also reported
-
3
-3
240 mAh cm ; Te: 2621 mAh cm ) to S.
3
that Se and Te have higher utilization rate, better
electrochemical activity and faster electrochemical reaction
terms of specific energy. Elemental sulfur
nontoxic has been considered to be one of the most
promising cathode materials because of its high theoretical
，abundant and
[10-12]
with Li than S.
Nevertheless, Se and Te have much lower
，
-1
theoretical gravimetric capacity (Se: 675 mAh g ; Te: 419 mAh
[13-15]
-1
-1
[1, 2]
g ) as compared with S.
The major stream of previous
specific capacity (1675 mAh g ).
However, the practical
studies on these chalcogen-based cathode materials has
focused on the structural design of S/Se/Te hosts, but
3, 4] molecular modification on the S/Se/Te-containing guests could
be a new way to improve the performance of the Li-chalcogen
batteries. Due to the above-mentioned opposite but
application of Li-S batteries is still restricted by their inherent
problems, including the insulating nature of S and the high
[
solubility of polysulfide intermediates into the electrolyte.
Many strategies, such as coupling S with porous carbons or
polar hosts, surface coating
S and choosing suitable
complementary features among these chalcogen elements,
heteroatomization of chalcogen molecules has been proposed
as an attractive strategy to obtain advanced comprehensive Li-
storage performances. However, rational integration and
design of the heteroatomic chalcogen molecules for advanced
lithium-chalcogen batteries is still great challenging.
electrolytes, have been employed to trap sulfur species in the
[5, 6]
cathode side.
Although improvements have been achieved,
the applications of sulfur cathodes are still suffered by its
-28
-1
intrinsically low electrical conductivity (5×10 S m ) and
limited long term cycling performance. Therefore, it is of great
importance to explore new high-energy cathode materials,
beyond the present S, with improved electronic conductivity
In addition to S/Se/Te hosts, the molecular structures and
electronic features of the different chalcogen-chalcogen bonds
in heteroatomic chalcogen molecules should be also critically
important on the performances of chalcogen-based cathode
Institute of Photovoltaics, Nanchang University, 999 Qianhu Road, Nanchang
3
30031, China.
Corresponding author. E-mail: sunfugen@ncu.edu.cn; lzhou@ncu.edu.cn.
materials. Heterocyclic Se
x y
S molecules with Se-S covalent
*
Electronic Supplementary Information (ESI) available: [XRD, N
results and electrochemical performances]. See DOI: 10.1039/x0xx00000x
2
sorption, XPS, DFT bonds have been reported to possess higher specific capacities
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than Se alone, and improved conductivity and cycling stability dissolved in 5.0 mL water containing 0.14 g concentrated
[20]
[
16-19]
compared to
S
alone.
Qian et al.
reported that
2 4
H SO . Then, 1.0 g SBA-15 was dispersed in the solution and
o
introducing a small amount of Se into S molecules could sonicated for 1 h. The mixture was heated at 100 C for 12 h
o
anchor S during cycling, and thus effectively reduce the and at 160 C for another 12 h, followed by repetition of
dissolution of polysulfides and shuttle effect. Similarly, a broad impregnation process once with another 5 mL aqueous
[22]
[
21]
class of Se
x
S
y
cathode materials, such as SeS
2
,
Se0.7S,
solution containing 0.8 g sucrose and 0.09 g H
2 4
SO . The
[23]
[24]
Se0.4
S
0.6
and Se
electrochemical performance. Recently, our group discovered carbonized at 900 C for 5 h in an Ar flow. To remove the SBA-
that the Se 8-n cathodes exhibited unique electrochemical 15 template, the carbonized product was stirred in a 5% HF
behavior rather than a simple hybrid of Li-S and Li-Se solution for 4 h. The as-prepared CMK-3 was collected by
2 5
S
demonstrated greatly improved obtained dark brown intermediate product was completely
o
n
S
[25]
batteries.
The selenium sulfide molecules are able to centrifugation, repeatedly washed by distilled water and finally
o
recover through the highly reversible conversion of dried at 80 C.
polysulfoselenide intermediates during discharge-charge Preparation of the Te
cycles. Density functional theory calculations (DFT) further
x
S1-x/CMK-3 composites
The TexS1-x/CMK-3 nanocomposites were prepared following a facile
melt-diffusion strategy. In a typical synthesis procedure, 0.97 g
sulfur (30.6 mmol) and 0.43 g tellurium (3.4 mmol) were mixed
homogeneously. The mixture was degassed in a vessel and then
reveal that heteroatomic selenium sulfide molecules with
higher polarizability could bind more strongly with hosts than
homoatomic sulfur molecules, which provides more efficient
suppression of the shuttling phenomenon and improvement of
electrochemical performance.
o
sealed under vacuum, followed by heating at 550 C for 4 h. The
obtained Te-S solid solution was homogeneously mixed with 0.60 g
CMK-3. The melt infiltration was further carried out in the vacuum-
sealed vessel at 550 °C for 12 h. In this work, by controlling the
composition of tellurium, sulfur and carbon in the precursors, three
composites with different Te/S mole ratios and a fixed Te-S solid
solution content (70 wt.%) were prepared, which were denoted as
In this sense, tellurium has higher polarizability and
[26-28]
conductivity than selenium.
anticipate that the Te-S bonds with higher polarizability could
enable heteroatomic Te molecules to promise better
lithium-chalcogen batteries. Herein, we demonstrate the
heteroatomic Te 1-x molecule with the highly heteropolar Te-S
bond as an attractive cathode material in the commerical and
low-cost carbonate-based electrolyte for the high- the composites.
performance lithium battery. The Te 1-x (x=0.05, 0.1 and 0.2) Material characterization
It is therefore rational to
x y
S
x
S
x
Te S1-x/CMK-3, where x/(1-x) represented the Te/S mole ratios in
x
S
molecules were homogeneously confined in the ordered
mesoporous carbons CMK-3 via a facile melt-impregnation
route starting from elemental Te, S and CMK-3. Due to the
The thermogravimetric analysis (TA Instrument Q600 Analyzer) of
samples was carried out in a nitrogen flow. The samples were
o
o
-1
heated to 800 C with a rate of 10 C min . The surface chemistry of
the samples was analysed using an Axis Ultra DLD X-ray
photoelectron spectroscopy. The X-ray source operated at 15 kV
introduction of Te atoms with higher
heteroatomic Te 1-x molecules have higher intrinsic electrical
conductivity than the homoatomic S molecules. The Te-S
p orbitals, the
x
S
8
-8
and 10 mA. The working pressure was lower than 2×10 Torr (1Torr
bonds could strongly anchor S in the CMK-3 frameworks, and
thus effectively reduce the formation and dissolution of
polysulfides, which could be also favorable for the fast
formation of stable electrode interfaces. Moreover, the Te-
containing polychalcogenide intermediates could induce the
formation of solid electrolyte interphase (SEI) layers on the
=
133.3 Pa). The C 1s, S 2p, Te 3d and Te 4s XPS spectra were
measured at 0.1 eV step size. The binding energies were calibrated
taking C 1s as a standard with a measured typical value of 284.6 eV.
The S 2p, Te 3d and Te 4s XPS signals were fitted with mixed
Lorentzian-Gaussian curves, and a Shirley function was used to
subtract the background using a XPS peak processing software. The
x
surfaces of Te S1-x/CMk-3 electrodes, which further pretect
polychalcogenides from dissolution and side reaction with X-ray diffraction (XRD) patterns were acquired on a Rigaku D/max
carbonate-based electrolytes. Therefore, the Te
1-x/CMK-3 2550 diffractometer operating at 40 KV and 20 mA using Cu Kα
x
S
composite with an optimal Te/S mole ratio exhibits excellent radiation (λ = 1.5406 Å). The FTIR analysis of the samples was
long-term cycling stability and high rate capability. These carried out using a BRUKER-VERTEX 70 instrument with high-
encouraging results suggest that the heteroatomization of sensitivity detector MCT. Nitrogen adsorption/desorption isotherms
chalcogen (such as S, Se, or Te) molecules in mesostructured
carbon hosts is promising strategy in enhancing the
were measured at 77 K with a Quadrasorb SI analyser. The
Brunauer-Emmett-Teller (BET) method was utilized to calculate the
specific surface area. The total pore volume was calculated using a
single point at relative pressure of 0.985. The pore size distributions
were derived from desorption branch by using the Barrett-Joyner-
Halenda (BJH) model. The morphologies of samples were observed
under scanning electron microscopy (SEM, JEOL 7100F) and
transmission electron microscopy (TEM, JEOL 2100F). The scanning
a
electrochemical performances of chalcogen/carbon-based
cathodes for Li batteries.
Experimental section
Preparation of CMK-3
The CMK-3 was prepared by a nanocasting method as transmission electronic microscope (STEM) was conducted on a
described in Nazar’s paper.
[29]
Typically, 1.25 g sucrose was Tecnai G2 F30.
2
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Electrochemical tests
as the S/CMK-3 and Te/CMK-3 composites, were obtained by
tuning the mole ratio of Te to S in the mixed precursors. The
total contents of Te and S in these composites were fixed at 70
wt. %. SEM images in Figure 1a-b display that the obtained
composites still retain the short rod-like morphology of CMK-3
The Te
x
S
1-x/CMK-3 samples were slurry-cast onto an aluminium
1-x/CMK-3 sample, 10
current collector. Typically, 80 wt. % of Te
x
S
wt. % carbon black (Super P Conductive Carbon Black) and 10 wt. %
sodium alga acid (SA) binder were mixed in water solvent. The areal
after Te and S loading. No Te0.1
were observed on the external surfaces of CMK-3, suggesting
0.9 were well penetrated into the mesoporous
channels of carbon hosts. There are no distinct differences
between the XRD patterns of the Te0.1 0.9/CMK-3 and CMK-3 in
Figure S2, indicating that the Te0.1 0.9 confined in the
S0.9 particle agglomerations
x
mass loadings of the Te S1-x/CMK-3 samples were all controlled to
-2
be 2.5-2.9 mg cm . The slurries were coated on aluminium current
the Te0.1
S
o
collectors and dried at 80 C overnight. Electrochemical tests of
these electrode materials were performed using coin cells with the
TexS1-x/CMK-3 cathodes and lithium metal as the counter
S
S
electrodes. The electrolyte was electrolyte was 1 M LiPF
in a mixture ofethylene carbonate (EC) and dimethyl carbonate
DMC) (1:1 by volume). The separator was a microporous
6
dissolved
mesopores are very small nanocrystals or in an amorphous
form. The relative ratios of Te to S and uniform distribution of
Te and S in the TexS1-x/CMK-3 composites can be further
(
membrane (Celgard 2400). The cell was assembled in an argon filled evidenced by STEM elemental mapping images in Figure 1c-e.
glove box. The galvanostatic charge-discharge tests and cyclic
voltammetry measurements (CV) were conducted using an Arbin
battery cycler (Arbin, BT2000, USA). Electrochemical impedance
spectroscopy (EIS) was performed with an electrochemical working
station PCI4/300 (Gamry Instrument, Warminster, PA, USA). The
sinusoidal excitation voltage applied to the coin cells was 5 mV,
with frequency range from 100 kHz to 0.01 Hz. All the
electrochemical tests were performed at room temperature.
2
-1
Figure 2. (a) Pore size distribution of CMK-3 (BET surface area=1110 m g , pore
3
-1
2
-1
volume=1.3 cm g ) and Te0.1
S
0.9/CMK-3 (BET surface area=55 m g , pore volume=0.1
3
-1
cm g ). (b) TGA and DTG curves of Te0.1 0.9/CMK-3, S/CMK-3 and Te/CMK-3.
S
Result and discussion
The porous structures of the Te
analyzed by N sorption. As shown in Figure 2a and S3, in
comparison with the pristine CMK-3, the specific surface area
and pore volume of the Te0.1 0.9/CMk-3 sample exhibit the
expected decrease, demonstrating the successful
incorporation of Te0.1 0.9 into the inner surface of the ordered
x
S1-x/CMk-3 samples were
2
S
S
mesoporous channels. TGA analysis in Figure 2b shows that all
samples exhibit a weight loss of approximately 70 wt. %
o
between 150 and 650 C in a nitrogen flow, corresponding to
the evaporation of Te and S during the heating process.
Moreover, the Te0.1S0.9 in the Te0.1S0.9/CMK-3 sample
evaporates at a intermediate temperature between that of the
Te/CMK-3 and S/CMK-3 samples, suggesting the possible
existence of Te-S interaction in the Te0.1
It is known that heteroatomic Te
covalent Te-S bonds are formed in molten mixtures of Te and S
S0.9/CMK-3 sample.
x
S1-x molecules with
[30-34]
at a high temperature.
To confirm the presence of Te-S
bonds in the Te 1-x/CMk-3 composites, the high resolution X-
x
S
ray photoelectron spectroscopy (XPS) analysis was conducted.
As shown in Figure 3a, the Te/CMK-3 sample presents
Figure 1. SEM images of (a) CMK-3 and (b) Te0.1
images of (c) Te0.05 0.95/CMK-3, (d) Te0.1 0.9/CMK-3 and (e) Te0.2
the magnified SEM image of CMK-3.
S
0.9/CMK-3. STEM elemental mapping characteristic Te 3d5/2 and 3d3/2 peaks located at
∼
573.6 and
584.0 eV for the Te-Te homopolar bond, accompanied by a
doublet signal at 576.5/ 586.9 eV for the Te-O bond which
S
S
S0.8/CMK-3. Inset in (a) is
∼
∼
∼
could be originated from the oxidized Te on the surface of the
The TexS1-x-based composites were prepared via a facile melt-
sample. However, in addition to the Te-Te and Te-O bonds, a
impregnation method, in which the melt tellurium and sulfur
o
were miscible with each other at 550 C in the vacuum-sealed
doublet peak at
574.7/ 585.1 eV, which corresponds to the Te-S heteropolar
bond, was deconvoluted and curve-fitted in the Te0.1S0.9/CMk-
a
intermediate binding energy of
∼
∼
vessel and then infiltrated into the order mesopores of CMK-3
(
The order mesoporous structure of CMK-3 is shown in Figure
S1) during the heating procedure. In this way, the TexS1-x/CMK-
composites with different x value of 0.05, 0.1 and 0.2, as well
3
sample. The existence of tellurium sulfide compounds in the
3
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Te0.1
S
0.9/CMk-3 sample was also evidenced by the S 2p XPS
spectras in Figure S4.
To further reveal the reaction and phase transition in the Te- carbonate-based electrolytes. We pay special attention to the
S mixtures during heating process based on the sulfur- integrated advantages of the heteroatomic Te in
tellurium binary phase diagram (Figure S5), XRD analysis was comparison with the homoatomic S or Te , confined in CMK-3
employed. As shown in Figure 3b, all the diffraction peaks of as cathode materials. As shown in the CV curves of the S/CMK-
the obtained bulk Te0.1 0.9 without the addition of CMK-3 are 3 sample (Figure S6), no oxidation and reduction current peaks
similar to the P2/c monoclinic phase of S , rather than the are observed after the first cathodic scanning. It is well known
mixed precusors of the Fddd orthorhombic S phase and the that such electrochemical incompatibility of the S/CMK-3
P3121 hexagonal Te phase. It has been known that the sample in the carbonate-based electrolytes should be due to
monoclinic phase (S ) usually exists only at high temperatures (> the polysulfide consumption by an undesired chemical
5.3 C), and only the orthorhombic (S ), rhombohedral (S reaction with carbonates which occurs when the polysulfides
and hexagonal (S ) phases are stable at room temperature. dissolve into the electrolytes to form single-phase
However, for the Te0.1S0.9/CMK-3 sample (Figure
The electrochemical properties of the Te
x
S1-x/CMK-3 (x=0.05,
0.1 and 0.2) composites were evaluated in the conventional
x 1-x
S ,
8
8
S
8
8
8
o
9
8
6
)
35]
[
a
8
[36, 37]
Therefore, it is deduced that the Te doping into S molecules solution.
8
endow the monoclinic phase with improved room- 4a), in addition to two reduction peaks at 2.3 and 1.6 V in the
temperature stability. The obtained monoclinic TexS1-x consists first cathodic process, one intense oxidation peak at 2.0 V is
of 8-membered cyclic molecules, where the Te and S atoms also present in the subsequent anodic process, suggesting the
appear to be struggling for the atomic positions. The possible high electrochemical reversibility of the Te0.1S0.9/CMK-3
crystal structure of the P2/c monoclinic phase Te0.1S0.9 is sample in the carbonate-based electrolytes. It has been
shown in Figure 3c. Statistically, the struggle and occupation of reported that polytellurides can also react with carbonates,
Te and S over the whole molecules guarantee their uniform but form the solid electrolyte interface (SEI) layers on the
[38, 39]
cathode surfaces.
distribution in the final amorphous TexS1-x/CMK-3 sample.
Therefore, it is deduced that the high
electrochemical reversibility of the Te0.1S0.9/CMK-3 sample
should be owing to the Te-induced formation of SEI layers on
the Te0.1S0.9/CMK-3 surfaces.
Density functional theory calculations (DFT) were conducted
to calculate the binding energy of the carbons with Te-S
containing species, as shown in Figure S7. It is revealed that
the Te-S bonds could strongly anchor S in the CMK-3
frameworks and effectively reduce the formation and
dissolution of polysulfides, which could be also favorable for
the fast formation of stable electrode interfaces, as well as the
SEI layers. In the CV curves of the Te0.1S0.9/CMK-3 sample
(Figure 4a), the reduction peak at 2.3 V in the first cathodic
process is corresponding to the conversion of Te0.1S0.9 to
polysulfides, polytellurides and possible new intermediates of
polysulfotellurides (Li Te S , 4 ≤ x + y ≤ 8) generated by the
2
x y
disproportionate reactions in the Te-S system; the reduction
peak at 1.6 V in the first cathodic process is attributed to the
conversion of polysulfides/polytellurides/polysulfotellurides to
Li S/Li Te. In the second and subsequent cycles of the
Figure 3. (a) High-resolution Te 3d XPS spectras of Te0.1
XRD patterns of the bulk Te, bulk S and as-prepared bulk Te0.1
of CMK-3. (c) Possible crystal structure of the monoclinic phase Te0.1
S
0.9/CMK-3 and Te/CMK-3. (b)
0.9 without the addition
0.9 at different
2
2
S
Te0.1S0.9/CMK-3 sample, only one pronounced reduction and
oxidation peaks centered at 1.8 V and 2.0 V, respectively, are
clearly observed. Such one-step reduction and oxidation
process is also observed for the sulfur encapsulated in the
S
view orientations. The yellow and red balls in (c) represent the S and Te atoms,
respectively.
[40, 41]
micropores where electrolyte solvent is deficient.
indicated that the conversion process between Li S/Li
It is
2
2
Te and
Te0.1
S
0.9 after the SEI coating is dominated by the one-step
“
quasi-solid-state” reaction mechanism which involves the
desolvation of Li ions before migrating through the SEI layer.
The overlapped redox onset potential after the first cycle
promises the excellent electrochemical reversibility of the
Te0.1S0.9/CMK-3 sample under the protection of the in-situ
-
1
Figure 4. (a) CV curves of Te0.1
S
0.9/CMK-3 at 0.1 mV s . (b) Schematic diagram of the Te-
formed SEI layer, which prevent the polychalcogenides from
shuttling and irreversibly reacting with the carbonates (Figure
induced formation of SEI layers on the Te
x
S1-x/CMK-3 electrode surfaces.
4b).
4
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The discharge and charge properties of the Te
x
S
1-x/CMK-3
The Te-induced formation of the SEI layer on the Te
/CMK-3 surface in the carbonate-based electrolyte, was
electrolytes at a current density of 250 mA g were further further demonstrated by the survey XPS spectra of the
investigated. As shown in Figure 5a and S8, two discharge Te0.1 0.9/CMK-3 electrode after the first discharge-charge cycle
plateaus and one charge plateaus are clearly observed in the at 3.0 V. As shown in Figure 6a, the Na XPS peak in both the
first cycle for the Te 1-x/CMK-3 samples. The electrochemical fresh and the cycled Te0.1 0.9/CMK-3 electrodes is resulted
beheviors of the Te 1-x/CMK-3 samples are different from that from the sodium alginate binder. Compared with the fresh
x 1-
S
(
x=0.05, 0.1 and 0.2) composites in the carbonate-based
x
-1
S
x
S
S
x
S
of the S/CMK-3 sample which no longer work after the first electrode, the obviously increased O content and the presence
discharge, as shown in Figure 5b. These two discharge plateaus of strong F XPS peak in the cycled electrode, further prove the
in the first cycle of the Te
attributed to the formation of polysulfides, polytellurides and on the cycled Te0.1
polysulfotellurides at 2.3 V, and the formation of Li S/Li Te at composition of the SEI layer on the cycled Te0.1
.6 V, respectively. The single voltage plateau in the second surface is further revealed by the FTIR spectra in Figure S9. The
x
S
1-x/CMK-3 composites could be formation of the SEI layer with the F/O-containing components
0.9/CMK-3 surface. The chemical
0.9/CMK-3
S
2
2
S
1
and subsequent cycles of the TexS1-x/CMK-3 composites could TEM and STEM elemental mapping images (Figure 6c-d) of the
be corresponding to the “quasi-solid-state” reaction path, cycled Te0.1S0.9/CMK-3 electrode show that the amorphous SEI
which agrees well with the CV results. The initial discharge and layer with
a thickness of ~ 10 nm is coated on the
charge capacities of the Te0.1S0.9/CMK-3 sample are 1250 and Te0.1S0.9/CMK-3 surface. Furthermore, the existence of charge
-
1
9
89 mAh g , respectively, corresponding to a large initial transfer resistance of the SEI layer on the cycled Te0.1S0.9/CMK-
-1
irreversible capacity of 261 mAh g . Such large initial 3 electrode is confirmed by the EIS analysis, as shown in Figure
irreversible capacity should be due to the formation of the SEI 6b. Instead of the only one semicircle in the EIS spectra of the
layer through the irreversible reaction of carbonates with fresh electrode, two depressed semicircles were observed for
polytellurides and polysulfotellurides in the first cycle. In the the cycled Te0.1S0.9/CMK-3 electrode, suggesting the “two RC
second and third cycle, the Te0.1S0.9/CMK-3 sample still exhibits parallel circuits”-typed electrochemical impedance behavior of
-1
the high discharge capacities of 995 and 960 mAh g , the cycled Te0.1S0.9/CMK-3 electrode. The semicircles of the
respectively, with the high coulombic efficiencies of 96.0% and high- and middle-frequency ranges in the EIS spectra of the
99.0%. These imply that the TexS1-x molecules confined in the Te0.1S0.9/CMK-3 electrode are corresponding to the charge
CMK-3 possess high electrochemical activity and reversibility transfer resistances of the SEI layer and the electrode material,
after the formation of effective SEI layers on the electrode respectively. The overlapped EIS spectras of the Te0.1S0.9/CMK-
surfaces.
3 electrode after varied cycles further confirm the formed SEI
layer is highly stable on the Te0.1S0.9/CMK-3 surface. The stable
SEI layer combined with the CMK-3 framework could
effectively
prevent
the
polysulfides/polytellurides/polysulfotellurides from dissolving
and irreversibly reacting with the carbonate-based electrolyte,
which is expected to improve the cycling stability of the TexS1-
x/CMK-3 electrode.
Figure 5. The charge-discharge curves of (a) Te0.1S0.9/CMK-3 and (b) S/CMK-3 at 250 mA
-
1
g .
−
1
Figure 7. (a) Cycling performance of Te
b) Rate performances of Te 1-x/CMK-3 at different current densities. (c) Long-term
cycling performance of Te 1-x/CMK-3 at 1 and 3 A g . Inset in (a) shows the coulombic
efficiency of Te0.1 0.9/CMK-3 at 250 mA g
x
S1-x/CMK-3 (n = 0.05, 0.1 and 0.2) at 250 mA g .
(
x
S
-
1
x
S
Figure 6. (a) The survey XPS spectras of the fresh and cycled Te0.1
after 1 cycle at 3.0 V). (b) EIS of the fresh and cycled Te0.1 0.9/CMK-3 electrode. (c) TEM
and (d) STEM elemental mapping images of the cycled Te0.1 0.9/CMK-3 electrode.
S
0.9/CMK-3 electrode
−1
.
S
(
S
S
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ARTICLE
Journal Name
The cycle performances of the Te
x
S1-x/CMK-3 (x=0.05, 0.1 polychalcogenides from dissolution and irreversible reaction
and 0.2), S/CMK-3 and Te/CMK-3 composites in the carbonate- with carbonates. As Te and S are infinitely miscible, with many
-
1
based electrolyte at 250 mA g are compared in Figure 7 and readily available solid solutions, the heteroatomic Te
S10. The Te0.1 0.9/CMK-3 sample exhibits the best cathodes represent a broad class of battery electrodes, which
electrochemical performance with the highest reversible could pave the way for promising opportunities to enable high
x y
S -based
S
-1
capacity of 845 mAh g after 100 cycles (Figure 7a). A high energy batteries for transportation and grid applications.
coulombic efficiency of 99.6% is also obtained for the
Te0.1
S
0.9/CMK-3 sample after 100 cycles (Inset of Figure 7a),
revealing the diminished shuttle effect and side reaction
between polychalcogenides and carbonate-based electrolytes. There are no conflicts to declare.
The cycling of the Te0.1 0.9/CMK-3 sample is also quite stable at
the higher rates of 1 and 3 A g , with stable capacities of 485
Conflicts of interest
S
-1
-1
and 387 mAh g achieved after 500 cycles (Figure 7c). When Acknowledgements
the reversible capacity, the initial coulombic efficiency, the
This work was financially supported by National Natural
Te/Se/S loading and the used electrolyte are all considered,
the electrochemical performance of the Te0.1
Science Foundation of China (No. 51502090), Natural Science
Foundation of Jiangxi Province (No. 20171BAB216007) and
Jiangxi Provincial Education Department Technology Landing
Program (No. KJLD14008).
S
0.9/CMK-3
sample is among the best series of chalcogen-based cathode
materials in the commerical and low cost carbonate-based
electrolyte (as listed in Table S1). In addition, the expected
decline in the specific capacity is found by increasing the Te/S
mole ratio from 1/9 to 2/8 in the Te
undoubtedly due to the limitation of the theoretical capacity,
as shown in Figure S11. The Te0.1 0.9/CMK-3 sample also
presents excellent cycling response to continuously varying
x
S1-x/CMK-3 composites,
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Journal of Materials Chemistry A
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Table of Contents
A stable cathode material in a conventional carbonate-based electrolyte was successfully
fabricated by homogeneously confining heteroatomic Te 1-x molecules into CMK-3.
x
S
1