Flexible self-supporting interconnected cobalt sulfide nanosheets enable high-loading and long-cycling Li-S batteries with high areal capacity

Abstract

Lithium-sulfur batteries (LSB) with high theoretical specific capacity/energy density still face some practical challenges, for instance shuttle effect, sluggish redox kinetics and corrosion of Li anode, which leads to rapid capacity decay. To overcome these challenges, herein, a porous and flexible sulfur host composed of interconnected Co 9 S 8 nanosheets in-situ grown on carbon cloth surface was constructed by a one-pot solvothermal method and applied as binder-free self-supporting electrode of LSB. The interconnected carbon fiber skeleton and highly conductive Co 9 S 8 nanosheets can provide abundant electron-transport channels to ensure excellent electric conductibility for electrode. Meanwhile, the abundant adsorption and catalytic sites provided by Co 9 S 8 nanosheets can effectively inhibit dissolution of polysulfides and improve conversion kinetics of polysulfides, effectively suppressing “shuttle effect” and protecting Li anode. The interconnected Co 9 S 8 nanosheets can also offer adequate void to facilitate penetration for Li 2 S 6 solution/electrolyte, accelerate lithium-ion diffusion and accommodate volume expansion of sulfur, thus ensuring high sulfur utilization and remarkable cycle stability of electrode. The Co 9 S 8 -CC/Li 2 S 6 electrode achieves impressive lithium-storage performance, including high discharge capacity (1315.1 mA h g − 1 , 0.1 C), excellent rate capability (872.4 mA h g − 1 , 2 C) and outstanding cyclic stability (decay of 0.02%/cycle over 1500 cycles, 2 C). Under a high sulfur-loading of 6.2 mg cm − 2 , the Co 9 S 8 -CC/Li 2 S 6 electrode still delivers high discharge capacity (1115.1 mAh g − 1 , 0.1 C) and good cycling stability (decay of 0.129%/cycle during 200 cycles, 0.5 C). This study offers insights for rational designing and structure engineering of self-supporting metal sulfide based composite host for high-performance LSB application.

Full text

Page 1/25
Flexible self-supporting interconnected cobalt
sulde nanosheets enable high-loading and long-
cycling Li-S batteries with high areal capacity
Xiaohui Tian
Wuhan University of Science and Technology
Lukang Che
Wuhan University of Science and Technology
Mengdie Liu
Wuhan University of Science and Technology
Naomie Beolle Songwe Selabi
Wuhan University of Science and Technology
Yingke Zhou (  zhouyk@wust.edu.cn )
Wuhan University of Science and Technology
Research Article
Keywords: Co9S8 nanosheet, Self-supporting sulfur host, Strong adsorption ability, Highly-ecient
electrocatalysis
Posted Date: February 22nd, 2023
DOI: https://doi.org/10.21203/rs.3.rs-2552696/v1
License:   This work is licensed under a Creative Commons Attribution 4.0 International License. 
Read Full License

Page 2/25
Abstract
Lithium-sulfur batteries (LSB) with high theoretical specic capacity/energy density still face some
practical challenges, for instance shuttle effect, sluggish redox kinetics and corrosion of Li anode, which
leads to rapid capacity decay. To overcome these challenges, herein, a porous and exible sulfur host
composed of interconnected Co9S8 nanosheets in-situ grown on carbon cloth surface was constructed by
a one-pot solvothermal method and applied as binder-free self-supporting electrode of LSB. The
interconnected carbon ber skeleton and highly conductive Co9S8 nanosheets can provide abundant
electron-transport channels to ensure excellent electric conductibility for electrode. Meanwhile, the
abundant adsorption and catalytic sites provided by Co9S8 nanosheets can effectively inhibit dissolution
of polysuldes and improve conversion kinetics of polysuldes, effectively suppressing “shuttle effect”
and protecting Li anode. The interconnected Co9S8 nanosheets can also offer adequate void to facilitate
penetration for Li2S6 solution/electrolyte, accelerate lithium-ion diffusion and accommodate volume
expansion of sulfur, thus ensuring high sulfur utilization and remarkable cycle stability of electrode. The
Co9S8-CC/Li2S6 electrode achieves impressive lithium-storage performance, including high discharge
capacity (1315.1 mA h g− 1, 0.1 C), excellent rate capability (872.4 mA h g− 1, 2 C) and outstanding cyclic
stability (decay of 0.02%/cycle over 1500 cycles, 2 C). Under a high sulfur-loading of 6.2 mg cm− 2, the
Co9S8-CC/Li2S6 electrode still delivers high discharge capacity (1115.1 mAh g− 1, 0.1 C) and good cycling
stability (decay of 0.129%/cycle during 200 cycles, 0.5 C). This study offers insights for rational
designing and structure engineering of self-supporting metal sulde based composite host for high-
performance LSB application.
1 Introduction
With continuous consumption of non-renewable fossil energy and environmental pollution, it is
particularly important to develop high energy density electrode materials and clean electrochemical
energy-storage system to meet the rapid development of smart grids and electric automobiles [1–4].
Lithium-sulfur batteries (LSB) with Li metal anode and sulfur cathode possess high theoretical specic
capacity (1675 mAh g− 1) and energy density (2600 Wh kg− 1), abundant sulfur reserves, low cost,
environmental friendliness, and are ideal new generation high energy density batteries [5, 6]. Nevertheless,
Li-S batteries still face challenges of the dissolution and shuttle effect of the intermediate product lithium
polysuldes (LiPSs), insulative properties of sulfur/Li2S, sluggish redox kinetics, high volume expansion,
low areal sulfur-loading and Li anode corrosion [7–10].
To conquer these challenges, several strategies including construction of sulfur composite cathodes,
designing of functional separators, protection of Li metal and application of electrolyte additives have
been proposed [11–17]. Various carbon matrixes, including carbon nanober, carbon nanotube, carbon
cloth and graphene, have been applied to encapsulate sulfur to construct the composite sulfur cathode
[18–21]. Among them, the 3D conductive carbon skeleton of carbon cloth (CC) possesses high
mechanical strength, high conductivity and elasticity, which is benecial to decrease damage from

Page 3/25
volume expansion/contraction, accelerate ion/electron transport, and has great potential as the exible
self-standing sulfur host (without conductive agent, current collector and binder) in LSB [22–24].
However, the surface of the carbon ber comprising the carbon cloth is naturally dense and non-porous,
resulting in a small specic surface area and lower polysuldes adsorption capacity compared to other
carbon matrix such as graphene. Meanwhile, the weak physical adsorption of the non-polar carbon ber
surface cannot effectively inhibit the diffusion of lithium polysuldes during long cycling, especially for
high sulfur-loading LSB [22]. Therefore, it is necessary to modify the structure or surface of carbon cloth
to gain high performance LSB.
A variety of transition-metal compounds (oxides, suldes, nitrides, carbides, phosphides) have
demonstrated powerful chemical adsorption for sulfur species and can accelerate redox conversion
kinetics in Li-S batteries [25, 26]. However, the electric conductivity of most metal compounds is low,
which greatly hinders transport of electrons and reduces the sulfur utilization and rate capability.
Recently, the metallic Co9S8 has attracted attention for its intrinsic conductivity, strong LiPSs adsorption
and catalytic ability [27–29], but high-surface-area Co9S8 nanostructures need to be further designed to
maximize the active sites and fully exploit the adsorption and catalytic ability for lithium polysuldes.
Compared to 0-D nanoparticle and 1-D nanowire (nanotube, nanorod), the 2-D nanosheet demonstrates
large specic surface area and high structure stability for effective adsorption and catalysis. The
nanosheet assembled 3-D porous structure can further offer abundant pores to host the sulfur species
and shorten ion diffusion path to improve stability during cycling, and can also provide plenty of
continuous electron conduction paths for fast electrochemical reaction. Therefore, the nanosheet
assembled 3-D porous sulfur host is expected to signicantly improve the lithium storage performance of
LSB.
In this work, a three-dimensional self-supporting conductive carbon cloth decorated with in-situ grown
polar Co9S8 nanosheets (Co9S8-CC) was constructed for enhancing the performance of sulfur composite
cathode. The Co9S8 nanosheets in-situ grown on carbon cloth surface are interwoven into a porous
structure, which can offer sucient space to physically adsorb lithium polysuldes, increase
electron/lithium-ion diffusion, and accommodate volumetric change during electrochemical reactions.
Polar Co9S8 nanosheets can also chemically anchor lithium polysuldes and catalyze the lithium
polysulde conversion, therefore effectively inhibit the "shuttle effect" even under high sulfur loading. The
three-dimensional conductive carbon cloth substrate with good exibility can not only improve the
structural stability of the electrode, but also provide a porous interconnected conductive frame, which
helps rapid electron/ion transfer. The Co9S8-CC/Li2S6 composite cathode obtained by direct adsorption
of Li2S6 solution on Co9S8-CC (sulfur loading: 2.5 mg cm− 2) displays high discharge specic capacity
(1315.1 mAh g− 1, 0.1 C), excellent rate performance (872.4 mAh g− 1 for 2 C) and outstanding cycle
stability (decay of 0.02%/cycle for 1500 cycles, 2 C). Even at a high sulfur loading of 6.2 mg cm− 2, the
Co9S8-CC based composite cathode still shows good electrochemical performance (low decay of
0.129%/cycle during 200 cycles at 0.5 C and high specic capacity of 1115.1 mAh g− 1 at 0.1 C). This

Page 4/25
study indicates the rational design and effectivity of self-supporting metal-sulde based composite
cathode for high-performance and high-sulfur-loading LSB.
2 Experimental
2.1 Preparation for interconnected Co9S8 nanosheets
The commercially available textile carbon cloths were cut into required sizes and pre-treated with acetone,
ethanol and deionized water in sequence for further use. The Co9S8 nanosheets on CC substrate surface
(Co9S8-CC) were synthesized via a one-pot solvothermal method and subsequent calcination. In a typical
synthesis, cobalt (II) acetate tetrahydrate (1 mmol) and thiourea (0.5 mmol) were dissolved in ethylene
glycol (10 mL) under magnetic stirring to form a transparent solution, which was transferred into an
autoclave with pre-treated carbon cloth (2 × 3 cm) and kept for 5 h at 200°C. The CC was taken out from
the solution and washed after natural cooling, and dried for 6 h at 80°C in vacuum and annealed in Ar/H2
(650°C/3 h) to get Co9S8-CC composite. The calculated mass loading of Co9S8 is about 2 mg cm-2. For
comparison, the pristine carbon cloth (CC) was processed under the same conditions without addition of
cobalt (II) acetate tetrahydrate and thiourea.
2.2 Material characterization
Structure, morphology and composition of the samples were characterized by scanning electron
microscopy (SEM, PHILIPS XL30TMP), X-ray diffraction (XRD, Xpert Pro MPD diffractometer),
transmission electron microscopy (TEM, JEM-2000 UHR SETM/EDS), UV-Vis adsorption spectra
(Shimadzu UV-2600) and X-ray photoelectron spectroscopy (XPS, VG Multilab 2000 apparatus).
2.3 Electrochemical measurements
The obtained CC or Co9S8-CC samples were punched into circular disks (Φ: 14 mm) and used directly as
cathode. Celgard 2400 microporous polypropylene lm and Li metal were respectively used as separator
and anode. When assembling coin cells, 20 or 50 µL Li2S6/(DME + DOL) with the concentration of 1.0 M
(corresponding to 3.84 or 9.60 mg of S) were used as the catholyte, and 10 µL commercial electrolyte (1.0
M LiTFSI electrolyte solution in 1 : 1 DME/DOL, with 1 wt% of LiNO3 additive) was used as anolyte. The
nal areal sulfur-loading of the electrodes were respectively 2.5 and 6.2 mg cm− 2, corresponding to the
electrolyte/sulfur (E/S) ratios of about 7.81 and 6.25 µL mg− 1, respectively. A Neware BTS-5V50mA
battery test system was used to conduct galvanostatic charging-discharging measurements from 1.7 to
2.8 V. The specic capacity was calculated according to S mass in Li2S6/(DME + DOL) solution. A Bio-
Logic VMP3 electrochemical workstation was used to obtain the cyclic voltammetry (CV) curves (1.7 ~
2.8 V at 0.1 mV s− 1) and electrochemical impedance spectroscopy (EIS) curves (10 mHz ~ 100 kHz).
For symmetrical cells, CC or Co9S8-CC electrodes were used as identical working/counter electrodes
directly. 1.0 M LiTFSI in DOL/DME (1 : 1) solution with (or without) 0.5 M Li2S6 was used as electrolyte.

Page 5/25
CV measurements were performed from − 0.8 to 0.8 V at 100 mV s− 1, EIS spectroscopies were acquired
from 100 kHz to 10 mHz.
2.4 Adsorption experiment of Li2S6 solution
Li2S6 solution was prepared by mixing Li2S and sublimed S (1 : 5) in mixed solvent containing DME and
DOL (1 : 1), followed by stirring under argon atmosphere (60°C/6 h). The whole piece of CC or Co9S8-CC
samples with the same weight of 20 mg were individually soaked in 2 mL Li2S6 solution (1 mM in DME +
DOL) for 1 h and the corresponding digital photographs were recorded. In addition, the precipitates and
supernatant of mixtures were further investigated by XPS and UV-vis spectrophotometry.
2.5 Computational method
Density functional theory (DFT) with Vienna ab initio simulation package (VASP) was used to calculate
binding energies (
E
b) between LiPSs or S8 and Co9S8 (311) or graphene (001) [30]. Perdew-Burke-
Ernzehof (PBE) functional within generalized gradient approximation (GGA) was used to evaluate
exchange-correlation interaction [31, 32]. 1×2×1 Monkhorst Pack k-points were used to sample the
Brillouin zone and 400 eV energy cutoff for plane wave was used in geometry optimization calculations.
Total energy of 1×10− 4 eV and ionic force convergence of 0.05 eV/Å were used to optimize structures.
The (311) surface of Co9S8 containing 136 atoms and graphene (001) containing 48 atoms were chosen
as substrates, and a 15-Å vacuum thickness between slabs was used. To investigate the interaction
between LiPSs or S8 and Co9S8 (311) or graphene (001), the binding energies ( ) of LiPSs or S8 with
Co9S8 (311) or graphene (001) were calculated with the following equation [33]:
1
where , and are respectively total energies of substrate, LiPSs or S8
and substrate+LiPSs or S8, and more positive value indicates stronger binding energy between LiPSs
or S8 and Co9S8 or graphene from Eq.(1).
3 Results And Discussion
3.1 Materials characterization
Figure1a-c displays the synthesis process for in-situ grown interconnected Co9S8 nanosheets on the
surface of CC substrate. During the solvothermal process, the pre-treated CC substrate with plenty of
functional groups can adsorb Co2+ in solution by electrostatic attraction (Fig.1a). The Co2+ adsorbed on
the surface of CC can act as nucleation centre and further adsorb sulfur ions released by thiourea
hydrolysis to generate low crystallinity Co9S8 nucleus at the early stage of the solvothermal procedure.
With the extension of reaction time, the crystal growth gradually becomes a kinetic-controlling process,
Eb
Eb
=
E
(
sub
)+
E
(
LiPSsorS
8) −
E
(
sub
+
LiPSsorS
8)
E
(sub)
E
(
LiPSsorS
8)
E
(
sub
+
LiPSsorS
8)
E
b

Page 6/25
some nanosheets grow from the initial nucleation position and nally form the interconnected porous
structure of low crystallinity nanosheets due to the combined effects of heterogenous nucleation and
Owstald ripening [34]. After further calcination, the low crystallinity Co9S8 nanosheets were transformed
into high crystallinity Co9S8 nanosheets on the surface of CC (Fig.1b). The obtained Co9S8-CC composite
can be cut into circular disks and directly used as the cathode for LSB without using conductive additive,
binder and current collector (Fig.1c). The anisotropic high crystallinity Co9S8 nanosheets are in-situ
grown on conductive CC surface and form the porous structure, which is conducive to Li ion diffusion
and electron transport. Figure1d shows the optical photos of CC and as-synthesized Co9S8-CC
composite, indicating the good exibility of CC and the self-supporting Co9S8-CC
composite with in-situ grown Co9S8 nanosheets on CC substrate. XRD pattern for Co9S8-CC composite is
displayed in Fig.1e. Except for two distinct wide peaks originated from CC substrate marked with
asterisk, all diffraction peaks are assignable to the cubic-phase Co9S8 (JCPDS No. 86-2273) [35–37],
indicating that the phase-pure Co9S8 is successfully synthesized by the solvothermal method and
subsequent heat treatment.
Figure2. SEM images of the CC (a-c) and Co9S8-CC composite (d-f). (g-i) The corresponding elemental
mapping of Co, S and C elements from (f). TEM image (j) and HRTEM image (k) of Co9S8 nanosheets
separated from CC substrate.
adjacent carbon bers, which provides a porous conductive framework. The high-magnication SEM
images (Fig.2b and c) display the relatively smooth surface of carbon bers with an average diameter of
around 10 µm. Figure2d-f show the representative SEM images of Co9S8 grown on CC substrate,
indicating that the CC is uniformly covered with a layer of nanosheets, which is well aligned on the
substrate in a large scale. As revealed in Fig.2d and e, the uniformly grown porous Co9S8 nanosheets on
the carbon bers do not destroy the original structure of pristine CC, indicating the excellent structural
stability of the substrate. The high-magnication SEM image (Fig.2f) clearly shows that the Co9S8
nanosheets with thickness of 60–100 nm grown on the CC substrate intertwine to form a porous
structure with pore size of 0.5 to 1 µm, leading to an open and three-dimensional porous structure, which
is benecial to high sulfur-loading, electrolyte access and electron transport during electrochemical
reactions. Moreover, the corresponding EDX elemental mapping of C, Co and S elements (Fig.2g-i) further
shows the homogeneous distribution of all elements throughout the entire porous structure of Co9S8-CC
composite.
Further insights into the morphological and structural features of the as-obtained Co9S8 separated from
CC substrate by ultrasonication were obtained by TEM. As revealed in Fig.2j, the nanosheet-like
structures of Co9S8 are clearly observed and the nanosheets are randomly distributed and interconnected
throughout the visible region. High-resolution TEM image (Fig.2k) demonstrates high-crystalline nature
of Co9S8 nanosheets. As indicated, the interplanar spacings are 0.30 and 0.18 nm, matching well with
(311) and (440) planes of the cubic phase Co9S8 [38–40]. The porous and high-crystalline Co9S8

Page 7/25
nanosheets can offer abundant active surface to adsorb Li2S6 solution and achieve high-sulfur loading
when directly using as cathode in LSB.
3.2 Electrochemical performances
As shown in Fig.1c, the Li2S6 solution was directly dropped and adsorbed on CC and self-supporting
Co9S8-CC before assembling the coin cells to evaluate the electrochemical performance. The E/S ratio
and areal sulfur-loading of electrodes were 7.81 uL mg− 1 and 2.5 mg cm− 2, and the specic capacity is
based on sulfur mass. Figure3a exhibits galvanostatic discharge and charge curves for CC/Li2S6 and
Co9S8-CC/Li2S6 cathodes at 0.1 C. Two discharge platforms at ~ 2.35 and ~ 2.1 V are respectively related
to sulfur reduction to polysuldes (Li2S
x
, 4 ≤
x
≤ 8, dened as Δ
Q
1) and subsequent polysuldes
conversion to lithium suldes (Li2S2/Li2S, the corresponding discharge capacity is dened as Δ
Q
2), and
the Δ
Q
2/Δ
Q
1 ratio can be used to evaluate the electrocatalytic capability of lithium polysulde redox
reaction [41, 42]. The conversion of Li2S to sulfur corresponds to the platform of charge curve [43, 44]. As
shown in Fig.3a, the Co9S8-CC/Li2S6 electrode provides discharge capacity of 1315.1 mAh g− 1 at 0.1 C,
much larger than pristine CC/Li2S6 electrode (1098.8 mAh g− 1), implying the signicantly improved sulfur
utilization due to the polysuldes trapping of Co9S8 nanosheets. Meanwhile, the Co9S8-CC/Li2S6 cathode
displays smaller polarization value (167 mV) compared to CC/Li2S6 cathode (226 mV). The reduced
polarization and enhanced specic capacity demonstrate the accelerated electrochemical reaction
kinetics in LSB caused by Co9S8 nanosheets. Moreover, the Δ
Q
2/Δ
Q
1 ratio of Co9S8-CC/Li2S6 electrode is
calculated to be 2.23, higher than that of CC/Li2S6 electrode (1.89), further conrming that the
introduction of polar Co9S8 nanosheets can promote the conversion of sulfur to Li2S2/Li2S [45]. The
lithium storage behavior of Co9S8-CC
electrode without Li2S6 between 1.7 to 2.8 V was evaluated to reveal the possible capacity contribution
from Co9S8-CC. As shown in Fig. S1, the Co9S8-CC electrode only displays specic discharge capacities
of 35 mAh g− 1 initially and 20 mAh g− 1 after 100 cycles, indicating very minor capacity contribution of
Co9S8-CC host to the Li2S6-containing Co9S8-CC cathode.
Figure S2 and Fig.3b further show the discharge/charge curves and rate capability for both CC/Li2S6 and
Co9S8-CC/Li2S6 electrodes at different rates. As displayed in Figure S2a, Co9S8-CC/Li2S6 electrode
exhibits reversible discharge capacities of 1315.1, 1222.7, 1106.0, 1006.3 and 872.4 mAh g-1 at 0.1, 0.2,
0.5, 1 and 2 C, respectively. The capacity and polarization for Co9S8-CC/Li2S6 electrode are respectively
slightly decreased and increased with current density increasing, probably caused by the large ohmic
resistance under high current density [44]. The Co9S8-CC/Li2S6 electrode maintains the apparent charging
and discharging platforms and high discharge capacity even at high rate of 2 C, probably due to strong
adsorption of LiPSs on Co9S8 and the accelerated reaction kinetics between sulfur and Li2S2/Li2S by
Co9S8. In sharp contrast, the CC/Li2S6 electrode suffers from fast capacity attenuation under identical
rates (Figure S2b), displaying lower discharge capacities of 1098.8, 866.4, 660.4, 480.9 and 235.4 mAh g-

Page 8/25
1 at respectively 0.1, 0.2, 0.5, 1 and 2 C. No obvious discharge potential plateau appears at 2 C for the
CC/Li2S6 electrode due to large polarization, indicating that high-rate capability for LSB is dominated by
the kinetic factor. Moreover, the Co9S8-CC/Li2S6 cathode shows larger discharge specic capacities and
superior cyclic stability under the same conditions compared to CC/Li2S6 electrode (Fig.3b). These
results demonstrate that the introduction of Co9S8 nanosheets can greatly increase reaction kinetics of
polysuldes and enhance rate capability of LSB.
Figure3c shows the cyclic performance for CC/Li2S6 and Co9S8-CC/Li2S6 electrodes at 0.5 C. The Co9S8-
CC/Li2S6 electrode displays a reversible discharge capacity of 1105.4 mAh g-1 (coulombic eciency :
99%) at the rst cycle and remains 1050.3 mAh g-1 (coulombic eciency : 99%) even after 100 cycles
(corresponding to 95% capacity retention), indicating that the dissolution and shuttling of LiPSs are well
inhibited in the Co9S8-CC/Li2S6 battery due to the strong binding effect of LiPSs on polar Co9S8. In
contrast, the CC/Li2S6 electrode displays lower specic capacity (860.9 mAh g-1) and coulombic
eciency (97%) at the rst cycle. Meanwhile, after 100 cycles the specic capacity decreases rapidly and
remains only 63% (coulombic eciency89%), implying the greatly reduced sulfur utilization due to the
dissolution of LiPSs. The electrochemical impedance spectroscopy (EIS) of CC/Li2S6 and Co9S8-CC
/Li2S6 electrodes before and after cycling at 0.5 C were further tested to explore the charge-transfer
kinetics (Fig. S3). EIS curves before cycling shown in Fig. S3a are composed of a high-frequency
semicircle and a low-frequency inclined line. The rst and second intercepts of the semicircle and X-axis
are related to the electrolyte impedance (Re) of the cell and the charge transfer impedance (Rct) across the
interface between electrode and electrolyte, respectively, and the inclined line is associated to Warburg
impedance of Li-ion diffusion in the electrode (Wo) [46–48]. After 100 cyclings (Fig. S3b), another
semicircle appears in high-frequency region of both EIS curves, relevant to SEI lm formed on electrode
surface (Rs) [49]. Inset in Fig. S3b and Table S1 show the equivalent circuit and the electrode resistance
obtained by tting the experimental data, respectively. Before cycling, Re and Rct values of the Co9S8-
CC/Li2S6 electrode (3.9 and 14.6 Ω) are lower than those of the CC/Li2S6 electrode (4.5 and 34.4 Ω),
indicating that the highly conductive Co9S8 nanosheets grown uniformly on CC surface greatly promote
charge-transfer process of Co9S8-CC/Li2S6 cathode. After 100 cycling at 0.5 C, Re values of both
electrodes show a slight increase, probably due to the production of soluble LiPSs during the charging
and discharging processer, which leads to an increase of the electrolyte viscosity and resistance [50]. On
contrary, Rct values for both electrodes decrease sharply, which may be due to the chemical activation
process of dissolution and redistribution of the active materials, which greatly improve the contact of
active material/host. Furthermore, both Rs and Rct values of Co9S8-CC/Li2S6 electrode are 0.9 and 4.4 Ω,
much smaller than those of CC/Li2S6 electrode (12.7 and 13.6 Ω). These results indicate that chemical
interactions between metallic polar Co9S8 nanosheets and sulfur species signicantly enhance the
contact of Co9S8-CC/active material [50]. Fig. S3c and d further show the correlation between Zre and
ω
-1/2 of Co9S8-CC/Li2S6 and CC/Li2S6 cathodes before and after 100 cycles, where the slope reects
Warburg factor correlated with Li+ diffusion [11]. Slope for Co9S8-CC/Li2S6 cathode is much smaller

Page 9/25
compared to CC/Li2S6 cathode before and after cycling, indicating that the Li+ diffusion coecient of
Co9S8-CC/Li2S6 electrode is higher, attributed to the open porous structure formed by the interwoven
Co9S8 nanosheets which signicantly accelerates the diffusion rate of Li+.
Long-cycling stability for Co9S8-CC/Li2S6 cathode at high current density of 2 C is also obtained and
displayed in Fig.3d. High discharge specic capacity of 872.5 mAh g-1 with a high coulombic eciency
(99.9%) can be initially obtained for the Co9S8-CC electrode. After 1500 cycles, a discharge specic
capacity of 612.3 mAh g-1 (70.2% capacity retention) is maintained with 99.6% coulombic eciency and
a very low attenuation of 0.02%/cycle. The remarkable cyclic stability for Co9S8-CC/Li2S6 electrode may
be ascribed to the chemical action between Co9S8 nanosheets and LiPSs which can eciently prevent
dissolution of LiPSs and alleviate the shuttle effect, and the 3D interconnected porous structure which
can supply enough space to buffer the volumetric change during the charge-discharge processes. SEM
images for Co9S8-CC/Li2S6 electrode after 1500 cycles at 2 C are further investigated, as shown in Fig.
S4. The Co9S8-CC/Li2S6 electrode after long cycling still maintains the initial porous structure of
interconnected Co9S8 nanosheets on CC, implying the excellent structure stability for Co9S8-CC host.
The fast redox kinetics and the 3D interconnected porous framwork for Co9S8-CC host are also benecial
to construct high sulfur-loading electrodes, which is vital for practical application of high-energy-density
LSB. High areal sulfur-loading Li-S cells (6.2 mg cm-2) were also constructed, and the corresponding rate
performance and cycling performance were investigated. As revealed in Fig. S5a and b, discharge
capacities for Co9S8-CC/Li2S6 electrode (6.2 mg cm-2) are respectively 1115.1, 966.4, 881.4, 700.9 and
435.4 mAh g-1 at rates of 0.1, 0.2, 0.5, 1 and 2 C. When returning to 0.1 C, a reversible discharge capacity
of ~ 1000.2 mAh g-1 is still retained, indicating the outstanding rate capability and excellent cycle
durability. In addition, Co9S8-CC/Li2S6 electrode (6.2 mg cm-2) also displays outstanding cycle stability at
0.5 C (Fig. S5c). Discharge capacity for Co9S8-CC/Li2S6 electrode still maintains 654.8 mAh g-1 after 200
cycles, which corresponds to a high areal capacity of about 4 mAh cm-2, capacity retention rate of about
74.3% and capacity decay of about 0.129%/cycle. The impressive specic capacity and stability indicate
that the self-supported porous composite structure composed of polar Co9S8 nanosheets and highly
conductive CC can effectively immobilize the soluble LiPSs and greatly reduce “shuttle effect” even at
high sulfur-loading. Compared to previously reported LSBs based on Co9S8 composite hosts shown in
Fig.3e and Table S2 [27, 36, 37, 39, 51–56], the self-supporting Co9S8-CC/Li2S6 battery possesses
superior areal and mass discharge specic capacities, outstanding rate performance and excellent cycle
performance, which is hopeful for application in high-performance LSBs.
3.3 Adsorption of LiPSs by Co9S8 nanosheets
In order to conrm the adsorption of Co9S8 nanosheets in Co9S8-CC composite for LiPSs, the cells with
the self-supporting CC and Co9S8-CC cathodes were disassembled after 100 cycles at 0.5 and the
separators were taken out to investigate. The corresponding optical photos of separators were shown in

Page 10/25
Fig. S6. The colour change of the separator can be attributed to dissolution and shuttling of soluble
LiPSs in electrolyte during the charging/discharging processes. As shown in Fig. S6, compared to the
yellow separator used in the CC/Li2S6 cell (Fig. S6a), the colour change of separator used in the Co9S8-
CC/Li2S6 electrode is nearly negligible (Fig. S6b), indicating that the porous structure formed by the
interwoven Co9S8 nanosheets in-situ grown on the CC substrate can effectively adsorb soluble LiPSs
produced during charge/discharge processes and signicantly reduce dissolution and diffusion of
soluble LiPSs in the electrolyte.
During charge/discharge processes, surface corrosion of Li metal anode caused by LiPSs can be
considered as another indicator to evaluate the adsorption capability of cathode host. Fig. S7 shows SEM
images and S mappings for the Li metal anodes used in CC/Li2S6 and Co9S8-CC/Li2S6 cells after 100
cycles. As revealed in Fig. S7a, the Li metal anode surface of CC/Li2S6 cell suffers serious damage and
shows plenty of cracks. The formation of cracks may be caused by the corrosion effect of soluble LiPSs
on Li metal surface, indicating the weak adsorption of CC on soluble LiPSs [57]. The obvious S element
distribution on Li metal surface (Fig. S7b) further veries the substantial deposition of Li2S/Li2S2 on Li
metal surface. For Li metal used in Co9S8-CC/Li2S6 cell (Fig. S7c), the surface is remarkably smooth and
the corresponding S element distribution is rather small, indicating less deposition of Li2S/Li2S2 on Li
metal surface and conrming that polar Co9S8 nanosheets have a strong trapping ability for soluble
LiPSs and can eciently protect lithium anode during cycling processes.
20 mg of CC and Co9S8-CC composite were also respectively soaked in the as-prepared 2 mL Li2S6 (1
mM) solution and stood for 1 h to further compare the adsorption capability. As displayed in Fig.4a,
colour for Li2S6 solution containing pristine CC remains almost unchanged of bright yellow after 1 h.
However, colour for Li2S6 solution of Co9S8-CC becomes colorless after 1 h, indicating that the adsorption
capacity of Co9S8-CC is superior to that of pristine CC, due to the strong chemisorption of metallic and
polar porous Co9S8 nanosheets with LiPSs, which may benet catalytic conversion of soluble LiPSs and
stable cycling of the Co9S8-CC/Li2S6 electrode. The concentration variation of Li2S6 in the supernatant
obtained from the Li2S6, CC and Co9S8-CC samples after adsorption experiments for 1 h was further
determined by UV-vis spectroscopy (Fig.4b). Compared to the pristine Li2S6 solution, the intensities of
characteristic S62- peaks located at ~ 280 nm of CC and Co9S8-CC in the absorption spectra decrease
obviously after absorption for 1 h [22]. The much lower S62- peak intensity of Co9S8-CC than that of CC
implies again that the polar Co9S8 nanosheets possess strong anity and adsorption to trap LiPSs and
suppress the shuttle effect during charging/discharging processes [11].
XPS analysis of Co9S8-CC and Co9S8-CC + Li2S6 after the adsorption test was performed to evaluate
chemical interaction of Co9S8 and Li2S6. As displayed in Fig.4c, the Co 2
p
3/2 spectrum of Co9S8-CC
displays three peaks. Two peaks at 780.9 and 778.3 eV are originated from the spin-orbit doublets,
corresponding respectively to the Co atoms occupying the tetrahedral and octahedral sites of Co9S8 [29,

Page 11/25
52]. After adsorption of Li2S6 solution, the Co 2
p
3/2 peaks of Co9S8-CC + Li2S6 shift towards lower binding
energy of 777.4 and 778.6 eV (Fig.4c). The change of peak positions is resulted from the electron
transfer to Co atoms from Li2S6, demonstrating the strong chemical-interaction of Li2S6 and Co atoms in
Co9S8-CC + Li2S6 [29]. The comparison of high-resolution S 2
p
spectrum for both Co9S8-CC and Co9S8-CC
+ Li2S6 is displayed in Fig.4d. Both S 2
p
XPS peaks can be tted with four peaks of various sulfur
species. For Co9S8-CC, two peaks located at 162.5 and 161.5 eV correspond to 2
p
1/2 and 2
p
3/2 of S2- in
Co9S8, whereas a peak at 163.5 eV is ascribed to C-S-C bond originating from the interfaces between
carbon cloth and Co9S8. The peak at 168.6 eV corresponds to SO42-, which is related to the partly oxidized
sulfur species on the surface of material [58, 59]. After the Li2S6 solution adsorption on Co9S8-CC, the
corresponding 2
p
3/2 and 2
p
1/2 for S2- in Co9S8-CC + Li2S6 are located at 161.8 and 163.0 eV. The overall
positive shift implies chemisorption of Li2S6 on Co9S8 surface [50]. Meanwhile, the enhanced SO42- peak
further conrms more Li2S6 adsorption on Co9S8-CC [60]. The XPS analysis indicates the strong chemical
anity of polar Co9S8 nanosheets to LiPSs, which may play a critical role in chemically capturing LiPSs
instead of physically preventing the loss of LiPSs.
The adsorption mechanism of polar Co9S8 with LiPSs and S8 was further probed through DFT
calculations. Figure5 and Fig. S8 exhibit the optimal congurations and corresponding binding energies
of different LiPSs and S8 clusters adsorbed on Co9S8 (311) and graphene (001). As displayed in Fig. S8,
the binding energies of LiPSs and S8 on graphene (001) are less than 1, indicating that the carbon-based
substrate cannot x LiPSs (S8) in Li-S batteries through strong chemical bonds [61]. The binding energies
of Li2S, Li2S2, Li2S4, Li2S6, Li2S8 and S8 clusters on Co9S8 (311) are about 5.39, 7.15, 7.32, 5.92, 7.29 and
6.04 eV, respectively (Fig.5a-f), much higher than those on graphene (001) (Fig.5g), implying that the
polar Co9S8 possesses much stronger anchoring ability for LiPSs and S8 compared to graphene. New Li-
S and S-Co bonds between LiPSs or S8 and Co9S8 (311) can be observed and are ascribed to the bonds
between Li atom of LiPSs and S atom of Co9S8 or between S atom of LiPSs (S8) and Co atom of Co9S8
due to the coulomb interaction of cation and anion [29]. The differential charge density analysis of the
adsorption system was further conducted to probe the charge transfer of LiPSs or S8 and Co9S8 (311)
(Fig.5). As shown in Fig. S9, the strong electron density accumulation on the newly formed S-Co and Li-S
bond is clearly observed, implying the formation of chemical bonds between LiPSs or S8 and
Co9S8 (311) [62]. Therefore, the introduction of Co9S8 can effectively anchor the LiPSs and S8 through
the strong chemical bonds during the charge/discharge processes in LSB, which is benecial to inhibit
shuttle effect and reduce the loss of active materials.
3.4 Redox kinetics analysis
Symmetrical cells with two identical electrodes were assembled to further explore catalytic effect of
Co9S8 on LiPSs conversion, and symmetrical cells without Li2S6 were also constructed. As displayed in
Fig.6a, symmetric cells of both CC and Co9S8-CC electrodes without Li2S6 display inappreciable current

Page 12/25
density, indicating the polarization curves mainly originate from the redox reaction of Li2S6 [43]. For
symmetrical cells with Li2S6, higher current density of the Co9S8-CC electrode with evident redox peaks is
clearly observed compared to CC electrode, indicating that Co9S8 plays a catalytic role in LiPSs
conversion [63]. Fig. S10 displays the EIS curves of symmetric cells with Li2S6. The Co9S8-CC
symmetrical cell displays much smaller Rct value than CC symmetrical cell, implying the enhanced
electrode reaction kinetics [64].
Figure6b displays CV proles of both CC/Li2S6 and Co9S8-CC/Li2S6 cathodes with the same sulfur-
loading at 0.1 mV s-1. Both proles exhibit representative lithiation/delithiation features of sulfur
cathodes with two cathodic peaks (Peak 1 and Peak 2) and one anodic peak (Peak 3), revealing the
transformation between sulfur and LiPSs. Compared to CC/Li2S6 cathode, Co9S8-CC/Li2S6 electrode
displays sharper peaks with higher intensities, indicating the improved charge transfer and redox
reaction. The corresponding peak potentials for lithiation/delithiation reactions of both CC/Li2S6 and
Co9S8-CC/Li2S6 electrodes are shown in Fig.6c. For Co9S8-CC/Li2S6 electrode, the peak potentials of
Peaks 1, 2 and 3 are respectively 2.32, 2.05 and 2.41 V (
vs
. 2.31, 1.97 V and 2.46 V for CC/Li2S6
electrode). The negative-shift anodic peak and positive-shift cathodic peak for Co9S8-CC/Li2S6 electrode
demonstrate that Co9S8 can effectively restrain the polarization of electrochemical reactions, which is
resulted
from the catalytic effect of Co9S8 on reduction/oxidation of S/Li2S [56]. Figure6d further displays the
corresponding variation of onset potentials, which is similar to that of peak potentials. The larger onset-
potential values in discharge process and smaller values in charge process for Co9S8-CC/Li2S6 electrode
indicate again the more favourable reaction kinetics of LiPSs because of the excellent catalytic effect of
Co9S8 for redox reaction of polysuldes [43]. Figure6e and f show the 1st and 5th CV proles for both
CC/Li2S6 and Co9S8-CC/Li2S6 electrodes at 0.1 mV s-1. Compared with the changed position and shape
of peaks of CC/Li2S6 electrode (Fig.6e), the Co9S8-CC/Li2S6 electrode displays almost identical position
and shape of peaks from the 1st to the 5th cycle (Fig.6f), demonstrating the reversible redox conversion
and high cyclic stability.
From the above results and discussion, the Co9S8-CC/Li2S6 electrode exhibits higher discharge capacity
and coulomb eciency, excellent cyclic stability and superior rate capability compared with CC/Li2S6
electrode. The enhancement of electrochemical performance for Co9S8-CC/Li2S6 electrode is mainly
attributed to the unique 3D multifunctional self-supporting Co9S8-CC structure that simultaneously acts
as the polar sulfur host, adsorber and catalyst. The corresponding electrochemical performance
improvement mechanism of Co9S8-CC host for LSB is displayed in Fig.7. The interconnected Co9S8
nanosheets grown uniformly on CC substrate can effectively adsorb soluble LiPSs and prevent them
from diffusion to the Li anode through abundant polar sites and high specic surface area, thus
inhibiting shuttle effect and protecting Li anode to ensure outstanding cyclic stability of LSB. The Co9S8
with both good conductivity and abundant catalytically active sites can promote electrochemical redox

Page 13/25
kinetics for LiPSs conversion and increase the active materials utilization. The integration of
nanostructured Co9S8 onto highly conductive carbon
cloth can greatly maximize the catalytic surface for LiPSs redox, provide rapid electron/Li+ transport
paths for redox reactions and improve the structural stability for sulfur composite host. The Co9S8-CC
composite is promising to serve as a self-supporting sulfur host for high-sulfur-loading and high-
performance LSB.
4 Conclusions
In conclusion, the self-supporting 3D interconnected Co9S8 nanosheets on conductive carbon cloth was
prepared and directly served as the high-eciency sulfur host for high performance LSB. Owing to the
synergistic effect between strong capture and catalytic ability of 3D interconnected polar Co9S8
nanosheets on LiPSs and the fast charge transfer from the carbon cloth substrate, the Co9S8-CC
composite sulfur host signicantly accelerates electron and Li ions transport, connes LiPSs and
enhance the redox kinetics, thus effectively inhibiting the shuttle effect during continuous charge and
discharge processes. The 3D porous structure composed of interconnected Co9S8 nanosheets provides
large space to effectively alleviate the volume change upon cycling and accommodate high content of
sulfur. Beneting from the excellent conductivity, high specic surface, strong adsorption and catalytic
ability, the Co9S8-CC/Li2S6 based Li-S batteries display excellent specic capacity, remarkable rate
capability and outstanding cyclic stability with low decay, even with high-areal sulfur loading. The self-
supporting metal sulde with unique structure and properties can be applied in high-performance LSB
and other energy storage and conversion devices.
Declarations
Author Contributions Xiaohui Tian and Lukang Che contributed equally to this work. Xiaohui Tian and
Lukang Che contributed to the material preparation, data collection and analysis, and writing - original
draft. Mengdie Liu and Naomie Beolle Songwe Selabi contributed to the investigation and formal
analysis. Yingke Zhou contributed to the validation, project administration and writing - review & editing.
All authors discussed the results and reviewed the manuscript.
Acknowledgements Authors are grateful to High-Performance Computing Center of Wuhan University of
Science and Technology for the numerical calculation.
Funding This work was supported by the National Natural Science Foundation of China (No. 51974209).
Competing interests The authors declare no competing interests.
References

Page 14/25
1. Dang CC, Mu Q, Xie XB, Sun XQ, Yang XY, Zhang YP, Maganti S, Huang MN, Jiang QL, Seok I, Du W,
Hou CX (2022) Recent progress in cathode catalyst for nonaqueous lithium oxygen batteries: a
review. Adv Compos Hybrid Ma 5:606–626
2. Wang YC, Chu FL, Zeng J, Wang QJ, Naren T, Li YY, Cheng Y, Lei YP, Wu FX (2021) Single atom
catalysts for fuel cells and rechargeable batteries: Principles, advances, and opportunities. ACS Nano
15:210–239
3. Chen L, Lin XH, Dang WQ, Huang H, Liu GX, Yang ZY (2023) Tantalum oxide
nanosheets/polypropylene composite separator constructing lithium-ion channels for stable lithium
metal batteries. Adv Compos Hybrid Ma 6:12
4. Maurya DK, Dhanusuraman R, Guo ZH, Angaiah S (2022) Composite polymer electrolytes: progress,
challenges, and future outlook for sodium-ion batteries. Adv Compos Hybrid Ma 5:2651–2674
5. Chen H, Wu ZZ, Zheng MT, Liu TC, Yan C, Lu J, Zhang SQ (2022) Catalytic materials for lithium-sulfur
batteries: mechanisms, design strategies and future perspective. Mater Today 52:364–388
. Liu YT, Liu S, Li GR, Gao XP (2021) Strategy of enhancing the volumetric energy density for lithium-
sulfur batteries. Adv Mater 33:2003955
7. Wang JL, Zhu YL, Wu N, Kan YC, Hu Y (2022) Designing thermotolerant and ame-resistant PAN-
based separator via surface engineering with heteroatoms doped carbon framework encapsulated
with CoS2 nanocatalysts towards safe lithium-sulfur batteries. Compos B Eng 233:109644
. Deng WJ, Phung J, Li G, Wang XL (2021) Realizing high-performance lithium-sulfur batteries via
rational design and engineering strategies. Nano Energy 82:105761
9. Wang P, Xi BJ, Huang M, Chen WH, Feng JK, Xiong SL (2021) Emerging catalysts to promote kinetics
of lithium-sulfur batteries. Adv Energy Mater 11:2002893
10. Gao WJ, Jin QW, Liu YY, Zhang YG, Wang X, Bakenov Z (2021) Promoting polysuldes redox
conversion by sulfur-decient ZnS1-x hollow polyhedrons for lithium-sulfur batteries. Mater Design
210:110060
11. Tian XH, Zhou YK, Zhang BY, Songwe Selabi NB, Wang GR (2022) Monodisperse polar NiCo2O4
nanoparticles decorated porous graphene aerogel for high-performance lithium sulfur battery. J
Energy Chem 74:239–251
12. Ng SF, Ling Lau MY, Ong WJ (2021) Lithium-sulfur battery cathode design: Tailoring metal based
nanostructures for robust polysulde adsorption and catalytic conversion. Adv Mater 33:2008654
13. Xie PF, Zhang BY, Zhou YK, Li P, Tian XH (2021) A dual-coated multifunctional separator for the high-
performance lithium-sulfur batterie. Electrochim Acta 395:139181
14. Liu Y, Wei HJ, Zhai XL, Wang F, Ren XY, Xiong Y, Akiyoshi O, Pan KM, Ren FZ, Wei SZ (2021)
Graphene-based interlayer for high-performance lithium-sulfur batteries: A review. Mater Design
211:110171
15. Angulakshmi N, Baby Dhanalakshmi R, Półrolniczak P, Walkowiak M, Xie PF, Tian XH, Zhou YK,
Manuel Stephan A (2020) An ecient bi-functional permselective separator coated with cubic type-

Page 15/25
Li7La3Zr2O12 and activated carbon for lithium-sulfur batteries. Sustain Energ Fuels 4:3500–3510
1. Zhao HJ, Deng NP, Yan J, Kang WM, Ju JG, Ruan YL, Wang XQ, Zhuang XP, Li QX, Cheng BW (2018)
A review on anode for lithium-sulfur batteries: Progress and prospects. Chem Eng J 347:343–365
17. Liu G, Sun QJ, Li Q, Zhang JL, Ming J (2021) Electrolyte issues in lithium-sulfur batteries:
Development, prospect, and challenges. Energ Fuel 35:10405–10427
1. Zhang XQ, He B, Li WC, Lu AH (2018) Hollow carbon nanobers with dynamic adjustable pore sizes
and closed ends as hosts for high-rate lithium-sulfur battery cathodes. Nano Res 11:1238–1246
19. Cheng XB, Huang JQ, Zhang Q, Peng HJ, Zhao MQ, Wei F (2014) Aligned carbon nanotube/sulfur
composite cathodes with high sulfur content for lithium-sulfur batteries. Nano Energy 4:65–72
20. Li BY, Xiao Q, Luo YZ (2018) A modied synthesis process of three-dimensional sulfur/graphene
aerogel as binder-free cathode for lithium–sulfur batteries. Mater Design 153:9–14
21. Tian XH, Cheng YN, Zhou YK, Zhang BY, Wang GR (2023) Long-cycling and high-loading lithium-
sulfur battery enabled by free-standing three-dimensional porous NiCo2O4 nanosheets. Appl Energ
334:120694
22. Wang MS, Yang H, Shen KQ, Xu H, Wang WJ, Yang ZL, Zhang L, Chen JC, Huang Y, Chen MY, Mitlin D,
Li X (2020) Stable lithium sulfur battery based on in situ electrocatalytically formed Li2S on metallic
MoS2-carbon cloth support. Small Methods 4:2000353
23. Tian CX, Wu JW, Ma Z, Li B, Zhang X, Zu XT, Xiang X, Li SA (2020) A melt-diffusion strategy for
tunable sulfur loading on CC@MoS2 for lithium-sulfur batteries. Energy Rep 6:172–180
24. Fu Y, Cheng K, Hu J, Zhou LM (2020) Integrating hierarchical porous nanosheets in the design of
carbon cloth-based sandwiched sulfur cathodes to achieve high areal capacity in lithium sulfur
batteries. Sustain Energ Fuels 4:3293–3299
25. Zhang XY, Zhang ST, Tan YJ g, Huang X, Pang H (2022) Recent advances and challenges of metal-
organic framework/graphene-based composites. Compos B Eng 230:109532
2. Li YY, Shapter JG, Cheng H, Xu GY, Gao G (2021) Recent progress in sulfur cathodes for application
to lithium-sulfur batteries. Particuology 58:1–15
27. Sun WW, Li YJ, Liu SK, Guo QP, Zhu YH, Hong XB, Zheng CM, Xie K (2020) Catalytic Co9S8 decorated
carbon nanoboxes as ecient cathode host for long-life lithium-sulfur batteries. Nano Res 13:2143–
2148
2. Liu YP, Ma SY, Liu LF, Koch JL, Rosebrock M, Li TR, Bettels F, He T, Pfnür H, Bigall NC, Feldhoff A, Ding
F, Zhang L (2020) Nitrogen doping improves the immobilization and catalytic effects of Co9S8 in Li-S
batteries. Adv Funct Mater 30:2002462
29. Dai CL, Lim JM, Wang MQ, Hu LY, Chen YM, Chen ZY, Chen H, Bao SJ, Shen BL, Li Y, Henkelman G, Xu
MW (2018) Honeycomb-like spherical cathode host constructed from hollow metallic and polar
Co9S8 tubules for advanced lithium-sulfur batteries. Adv Funct Mater 28:1704443
30. Perdew JP, Burke K, Ernzerhof M (1996) Generalized gradient approximation made simple. Phys Rev
Lett 77:3865–3868

Page 16/25
31. Nosé S (1984) A unied formulation of the constant temperature molecular dynamics methods. J
Chem Phys 81:511–519
32. Kresse G, Furthmüller J (1996) Ecient iterative schemes for ab initio total-energy calculations using
a plane-wave basis set. Phys Rev B 54:11169–11186
33. Pang Q, Kundu DP, Nazar LF (2016) A graphene-like metallic cathode host for long-life and high-
loading lithium-sulfur batteries. Mater Horiz 3:130–136
34. Liu GJ, Wang B, Wang L, Liu TF, Gao TT, Wang DL (2016) Facile controlled synthesis of a hierarchical
porous nanocoral-like Co3S4 electrode for high-performance supercapacitors. RSC Adv 6:54076–
54086
35. Ge RX, Chen L (2022) Ultra-small RuO2 nanoparticles supported on carbon cloth as a high-
performance pseudocapacitive electrode. Adv Compos Hybrid Ma 5:696–703
3. Xu JL, Liu L, Sun YH, Lu RF, Wan ZR g, Sun Q (2020) Engineering of three-dimensional nanohybrids:
Co9S8 nanocrystal coated hollow carbon nanosphere for advanced lithium storage. Appl Surf Sci
514:146092
37. Chen SX, Luo JH, Li NY, Han XX, Wang J, Deng Q, Zeng ZL, Deng SG (2020) Multifunctional
LDH/Co9S8 heterostructure nanocages as high-performance lithium-sulfur battery cathodes with
ultralong lifespan. Energy Storage Mater 30:187–195
3. Zhao SY, Tian XH, Zhou YK, Ma B, Angulakshmi N (2020) Three-dimensionally interconnected
Co9S8/MWCNTs composite cathode host for lithium-sulfur batteries. J Energy Chem 46:22–29
39. Chen L, Xie XF, Zhang ZA, Kong XZ, Liang SQ, Pan AQ (2020) One-pot synthesis of hetero-Co9S8-NiS
sheets on graphene to boost lithium-sulfur battery performance. Inorg Chem Front 7:2160–2167
40. Xi YK, Angulakshmi N, Zhang BY, Tian XH, Tang ZH, Xie PF, Chen GZ, Zhou YK (2020) A Co9S8
microsphere and N-doped carbon nanotube composite host material for lithium-sulfur batteries. J
Alloy Compd 826:154201
41. Yao WQ, Zheng WZ, Xu J, Tian CX, Han K, Sun WZ, Xiao SX (2021) ZnS-SnS@NC heterostructure as
robust lithiophilicity and sulphilicity mediator toward high-rate and long-life lithium-sulfur batteries.
ACS Nano 5:7114–7130
42. Li DM, Li HT, Zheng SM, Gao N, Li S, Liu J, Hou LL, Liu JC, Miao BB, Bai J, Cui ZM, Wang N, Wang B,
Zhao Y (2022) CoS2-TiO2@C core-shell bers as cathode host material for high-performance lithium-
sulfur batteries. J Colloid Interf Sci 607:655–661
43. Wang SZ, Liao JX, Yang XF, Liang JN, Sun Q, Liang JW, Zhao FP, Koo A, Kong FP, Yao Y, Gao XJ, Wu
MQ, Yang SZ, Li RY, Sun XL (2019) Designing a highly ecient polysulde conversion catalyst with
paramontroseite for high-performance and long-life lithium-sulfur batteries. Nano Energy 57:230–
240
44. Xu ZL, Lin SG, Onofrio N, Zhou LM, Shi FY, Lu W, Kang K, Zhang Q, Lau SP (2018) Exceptional
catalytic effects of black phosphorus quantum dots in shuttling-free lithium sulfur batteries. Nat
Commun 9:4164

Page 17/25
45. Xu J, Yang LK, Cao SF, Wang JW, Ma YM, Zhang JJ, Lu XQ (2021) Sandwiched cathodes assembled
from CoS2-modied carbon clothes for high-performance lithium-sulfur batteries. Adv Sci 8:2101019
4. Tian XH, Zhou YK, Tu XF, Zhang ZT, Du GD (2017) Well-dispersed LiFePO4 nanoparticles anchored on
a threedimensional graphene aerogel as high-performance positive electrode materials for lithium-
ion batteries. J Power Sources 340:40–50
47. Zhang BY, Zhao SY, Tang ZH, Xie PF, Angulakshmi N, Zhou YK, Tian XH (2022) High–performance
three–dimensional ower–like CoS/MWCNT composite host for Li-S batteries. J Solid State Electr
26:389–400
4. Tian XH, Zhou YK, Wu G, Wang PC, Chen J (2017) Controllable synthesis of porous LiFePO4 for
tunable electrochemical Li-insertion performance. Electrochim Acta 229:316–324
49. Li ZQ, Li CX, Ge XL, Ma JY, Zhang ZW, Li Q, Wang CX, Yin LW (2016) Reduced graphene oxide
wrapped MOFs-derived cobalt-doped porous carbon polyhedrons as sulfur immobilizers as cathodes
for high performance lithium sulfur batteries. Nano Energy 23:15–26
50. Chong WG, Huang JQ, Xu ZL, Qin XY, Wang XY, Kim JK (2017) Lithium-sulfur battery cable made
from ultralight, exible graphene/carbon nanotube/sulfur composite bers. Adv Funct Mater
27:1604815
51. Liu XF, Wang D, Yang XZ, Zhao ZZ, Yang H, Feng M, Zhang W, Zheng WT (2019) Synergistic dual-
connement effect: Merit of hollowly metallic Co9S8 in packaging enhancement of electrochemical
performance of Li-S batteries. ACS Appl Energy Mater 2:1428–1435
52. Chen T, Ma LB, Cheng BR, Chen RP, Hu Y, Zhu GY, Wang YR, Liang J, Tie ZX, Liu J, Jin Z (2017)
Metallic and polar Co9S8 inlaid carbon hollow nanopolyhedra as ecient polysulde mediator for
lithium-sulfur batteries. Nano Energy 38:239–248
53. Yu Y, Zhan ZH, Tang PJ, Xu QY, Fan Q, Wang W, Shen K (2021) Promoting polysulde redox kinetics
by Co9S8 nanoparticle-embedded in N-doped carbon nanotube hollow polyhedron for lithium sulfur
batteries. J Alloys Compd 869:159306
54. Wei J, Chen B, Su H, Jiang C, Li XT, Qiao SS, Zhang H (2021) Co9S8 nanotube wrapped with graphene
oxide as sulfur hosts with ultra-high sulfur content for lithium-sulfur battery. Ceram Int 47:2686–
2693
55. Wei J, Su H, Qin CM, Chen B, Zhang H, Wang JM (2019) Multifunctional Co9S8 nanotubes for high-
performance lithium-sulfur batteries. J Electroanal Chem 837:184–190
5. Tong W, Huang Y, Jia W, Wang X, Guo Y, Sun Z, Jia D, Zong J (2018) Leaf like interconnected network
structure of MWCNT/Co9S8/S for lithium-sulfur batteries. J Alloys Compd 731:964–970
57. Xie PF, Yang RY, Zhou YK, Zhang BY, Tian XH (2022) Rationally designing composite gel polymer
electrolyte enables high sulfur utilization and stable lithium anode. Chem Eng J 450:138195
5. Li MB, Zhou HH, Yang WJ, Chen L, Huang Z, Zhang NS, Fu CP, Kuang YF (2017) Co9S8 nanoparticles
embedded in a N, S co-doped graphene-unzipped carbon nanotube composite as a high performance
electrocatalyst for the hydrogen evolution reaction. J Mater Chem A 5:1014–1021

Page 18/25
59. Qiu J, He DY, Zhao R, Sun BL, Ji H, Zhang N, Li YZ, Lu XF, Wang C (2018) Fabrication of highly
dispersed ultrane Co9S8 nanoparticles on carbon nanobers as low-cost counter electrode for dye-
sensitized solar cells. J Colloid Interf Sci 522:95–103
0. Liu B, Huang S, Hu J, Kong D, Yang HY (2019) Bifunctional NiCo2S4 catalysts supported on a carbon
textile interlayer for ultra-stable Li-S battery. J Mater Chem A 7:7604–7613
1. Zheng Y, Li H, Yuan H, Fan H, Li W, Zhang J (2018) Understanding the anchoring effect of Graphene,
BN, C2N and C3N4 monolayers for lithium-polysuldes in Li-S batteries. Appl Surf Sci 434:596–603
2. Wang Q, Zhao HQ, Li BY, Yang CH, Li MY, Li YN, Han P, Wu MM, Li TY, Liu RP (2021) MOF-derived
Co9S8 nano-ower cluster array modied separator towards superior lithium sulfur battery. Chinese
Chem Lett 32:1157–1160
3. Yang CY, Li Y, Peng WC, Zhang FB, Fan XB (2022) In situ N-doped CoS2 anchored on MXene toward
an ecient bifunctional catalyst for enhanced lithium-sulfur batteries. Chem Eng J 427:131792
4. Pu J, Shen ZH, Zheng JX, Wu WL, Zhu C, Zhou QW, Zhang HG, Pan F (2017) Multifunctional
Co3S4@sulfur nanotubes for enhanced lithium-sulfur battery performance. Nano Energy 37:7–14
Figures

Page 19/25
Figure 1
(a-c) Schematic illustration for the synthesis of Co9S8-CC composite and assembly of Li-S cell. (d) Free-
standing and exible features of the CC and as-synthesized Co9S8-CC composite. (e) XRD pattern of
Co9S8-CC composite.

Page 20/25
Figure 2
SEM images of the CC (a-c) and Co9S8-CC composite (d-f). (g-i) The corresponding elemental mapping of
Co, S and C elements from (f). TEM image (j) and HRTEM image (k) of Co9S8 nanosheets separated from
CC substrate.

Page 21/25
Figure 3
(a) The initial galvanostatic discharge-charge proles of the CC/Li2S6 and Co9S8-CC/Li2S6 electrodes at
0.1 C. (b) Rate performance of the CC/Li2S6 and Co9S8-CC/Li2S6 electrodes at various rates. (c) Cycle
performance and the corresponding Coulombic eciency of CC/Li2S6 and Co9S8-CC/Li2S6 electrodes at
0.5 C. (d) Long-term cycling performance and the corresponding Coulombic eciency of Co9S8-CC/Li2S6

Page 22/25
electrodes at 2 C. (e) Comparison of rate capabilities of Li-S batteries based on Co9S8-CC (with different
sulfur loadings) in this work with other previously reported Co9S8 composite hosts.
Figure 4
(a) Adsorption ability comparison of CC and Co9S8-CC composite in the solution of Li2S6 in mixed
DME/DOL solvents. (b) UV-vis spectra of supernatant of Li2S6 solution after the adsorption test. High-
resolution XPS spectra of Co 2
p
3/2 (c) and S 2
p
(d) of both Co9S8-CC and Co9S8-CC+Li2S6.

Page 23/25
Figure 5
Optimal congurations and corresponding binding energies of (a) Li2S, (b) Li2S2, (c) Li2S4, (d) Li2S6, (e)
Li2S8 and (f) S8 adsorbed on Co9S8 (311). (g) Comparison of the binding energies of LiPSs or S8 on
graphene (001) and Co9S8 (311).

Page 24/25
Figure 6
(a) CV curves of CC and Co9S8-CC symmetric cells. (b) CV curves of CC/Li2S6 and Co9S8-CC/Li2S6
electrodes at a scan rate of 0.1 mV s-1. Comparison of the peak potentials (c) and onset potentials (d)
from the CV data in (b). The 1st and 5th CV curves of CC/Li2S6 electrode (e) and Co9S8-CC/Li2S6 electrode
(f) at 0.1 mV s-1.

Page 25/25
Figure 7
Electrochemical performance improvement mechanism of Co9S8-CC composite host for Li-S batteries.
Supplementary Files
This is a list of supplementary les associated with this preprint. Click to download.
Supportinginformation.docx