Supplementary Information
Ultrasmall Li2S Nanoparticles Anchored in Graphene Nanosheets for High-Energy
Lithium-Ion Batteries
Kai Zhang*, Lijiang Wang*, Zhe Hu, Fangyi Cheng & Jun Chen
* These authors contributed equally to this work.
Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), Collaborative
Innovation Center of Chemical Science and Engineering, Chemistry College, Nankai University,
Tianjin 300071, China
Correspondence
and
requests
for
materials
should
be
addressed
to
J.
C.
([email protected])
Author Contributions
K.Z. and L.W. designed the experiments, synthesized the materials, and performed the
characterization. K.Z., L.W., and Z.H. carried out the electrochemical tests. All authors
contributed to results analysis and manuscript preparation. J.C. and F.C. supervised and
directed the study.
Method
Synthesis of the graphene oxides. The graphene oxide (GO) is prepared via a Staudenmaier
method.1 Firstly, 30 mL of 65−68% HNO3 was placed in a three-necked flask with continued
stirring, and then 90 mL of 98% H2SO4 was slowly added in ice water bath. After 15 min, 2.5 g
of graphite powder was gradually added. When the mixture was stirred over 15 min, 12.5 g of
KMnO4 (purity 99%) was put into the suspension and stirred in ice water bath for about 60 min.
Afterwards the mixed solution was allowed to react for five days at 25 °C, 300 mL of de-ionized
water was slowly pour into the mixed solution. The above mixed solution was further stirred for
1 h followed by adding 15 mL of 30 wt % H2O2 (aq) and stirred for another 2 h. This suspension
S1
was continuously washed thoroughly with 1500 mL of 3% hydrogen peroxide for many times.
The resultant paste was dispersed in deioned water and then centrifuged to clear away impure
ions of oxidant origins. Finally, the obtained yellowish-brown graphite oxide dispersion was
frozen drying for 48 h under vacuum after the purification process was repeated ten more times.
Preparation of the Si thin film anode. Si thin film was deposited with a constant radio
frequency power supply of 100 W on the Cu foam substrate by using a JCP-350 magnetron
sputtering system according our previous reports.2, 3 The target was N-type monocrystalline Si
(99.99%). The distance from Si target to Cu foam in the sputtering system was fixed at 10 cm.
High-purity argon (99.999%) was introduced into the chamber after attaining a base pressure
of 5.010−4 Pa. The gas flow was 20 sccm and the working pressure was kept at 0.5 Pa during
sputtering. Before the deposition on the substrate, the target was pre-sputtered for 10 min to
remove the contaminants on the surface and then the Si thin film was obtained by sputtering for
1 h.
Figures
Figure S1. (a) Thermogravimetric analysis curves of the TG−S and in-situ TG−Li2S composites.
(b) XRD pattern of the in-situ TG−Li2S sample after heat treatment at 600 °C. The XRD result
demonstrates that the product was Li2SO4 after heating the in-situ TG−Li2S at 600 °C. The
reaction equation can be described as follows:
TG−S (C+S) + 2O2 → SO2↑ + CO2↑
(1)
TG−Li2S (C+ Li2S) + 3O2 → Li2SO4 + CO2↑
(2)
The S content is 62 wt.% for the TG−S composite. From the thermogravimetric curve of the
in-situ TG−Li2S composites, the mass increases by 60 wt.%. If the mass of the TG−Li2S is x and
the weight ratio of Li2S is y, we can write the equation as follow:
Molecular weight
Li2S
Li2SO4
46
110
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Mass
xy
(1+60%)x
xy
(1  60 %) x

46
110
(2)
According equation 2, the calculated y is 0.67, so the Li2S content is 67 wt.%.
Figure S2. Pore distribution plots obtained using the Barrett-Joyner-Halenda (BJH) method for
the TG (a), TG−S (b), and in-situ TG−Li2S (c).
Figure S3. SEM image of the ex-situ TG−Li2S composite with different magnifications.
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Figure S4. TEM images of the TG (a) and TG−S nanocompiste (b).
Figure S5. TEM (a) and HRTEM (b) images of the ex-situ TG−Li2S composite.
Figure S6. Initial potential barrier at 0.02C, 0.1C, and 0.5C (1C = 1166 mA g−1) for the in-situ
TG−Li2S (a) and ex-situ TG−Li2S (b) composites. For in-situ TG−Li2S cathode, the mass ratio of
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in-situ TG−Li2S composite: conductive carbon: binder is 8: 1: 1, with loading of ~53 wt.% Li2S
and ~1.3 mg Li2S/cm2. For ex-situ TG−Li2S cathode, the mass ratio of Li2S powder: TG:
conductive carbon: binder is 53: 27: 10: 10.
Figure S7. Cyclic performance of the in-situ TG−Li2S composite with polysulfide and LiNO3
(black), only polysulfide (red), only LiNO3 (blue), and no electrolyte additive (pink) at 0.02C
between 1.4 and 3.4 V for the first cycle and at 0.5C between 1.4 and 2.8 V for the subsequent
cycles. The mass ratio of in-situ TG−Li2S composite: conductive carbon: binder is 8: 1: 1, with
loading of ~53 wt.% Li2S and ~1.3 mg Li2S/cm2.
Figure S8. Cyclic performance of the in-situ TG−Li2S electrode with 95 wt.% in-situ TG−Li2S
composite and 5 wt.% PVdF binder. The mass ratio of Li2S in the electrode is ~64 wt.% with
loading of ~1.3 mg Li2S/cm2.
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Figure S9. Electrochemical impedance spectroscopy (EIS) for the cells made of the in-situ
TG−Li2S (a, c) and ex-situ TG−Li2S (b, d) composites tested after 10 cycles at different
temperatures and discharge states.
Figure S10. SEM images of the Si thin film on the Cu foam with different magnifications.
Figure S11. (a) Cycling performance of the Si/Li half cell at 0.2C and (b) the corresponding
S6
charge−discharge curves for the first, second, tenth, and fiftieth cycles.
Tables
Table S1. The discharge capacities at the 1st (C1), 2nd (C2), 10th (C10), 50th (C50), and the
100th (C100) cycles for the in-situ TG−Li2S
and ex-situ TG−Li2S composites at 0.02 C between
1.4 and 3.4 V for the first cycle and at 0.1C between 1.4 and 2.8 V for the subsequent cycles.
C1 (mAh g−1) C2 (mAh g−1)
C10 (mAh g−1)
C50 (mAh g−1)
C100 (mAh g−1)
In-situ
1119
953
864
814
791
933
771
632
514
452
TG−Li2S
Ex-situ
TG−Li2S
Table S2. Test values of our Li2S/Si full cell and comparison with previously reported full cells.
Specific capacity
Average discharge
(mAh g )
voltage (V)
Si thin film
900
1.7
LiNi0.5Mn1.5O4
Sn−C
120
4.0
4
LiFePO4
Li4Ti5O12
160
1.9
5
Li2S−C
Sn−C
600
1.6
6
482
1.7
7
Cathode
In-situ
TG−Li2S
Li2S/CMK-3
Anode
Si
nanowires
−1
Ref.
this
paper
Li4C8H2O6
Li4C8H2O6
208
1.8
8
LiCoO2
graphite
140
3.7
7
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