1

Supporting information for

MoS2 Nanosheets Decorated Ni3S2@MoS2 Coaxial Nanofibers: Constructing an Ideal

Heterostructure for Enhanced Na-Ion Storage

Jin Wanga,b

, Jilei Liu

b, Hao Yang

c,d,*,

Dongliang Chao

b, Jiaxu Yan

b, Serguei V. Savilov

e,

Jianyi Linf and Zexiang Shen

a,b,*

a Energy Research Institute (ERI@N), Interdisciplinary Graduate School, Nanyang

Technological University, Research Techno Plaza, 50 Nanyang Drive, 637553, Singapore

b Division of Physics and Applied Physics, School of Physical and Mathematical Sciences,

Nanyang Technological University, 21 Nanyang Link, 637371, Singapore

c School of Physics and Electronic Engineering, Jiangsu Normal University, Xuzhou, 221116

Jiangsu, P.R. China

d Jiangsu Key Laboratory of Advanced Laser Materials and Devices, Jiangsu Normal

University, Xuzhou, 221116 Jiangsu, P.R. China

e Department of Chemistry, M. V. Lomonosov Moscow State University, Moscow 119991,

Russia

f Energy Research Institute (ERI@N), Nanyang Technological University, 50 Nanyang Drive,

637553, Singapore

E-mail: Zexiang@ntu.edu.sg (Z.X. Shen)

E-mail: yanghao@jsnu.edu.cn (H. Yang)

Keywords: molybdenum sulfide, Ni3S2, graphene, core/shell, sodium ion batteries

2

Materials and Methods

Growth of Ni/Graphene foams: The growth of Ni/graphene foams (Ni/GF) was achieved by chemical

vapor deposition (CVD) using First Nano's EasyTube 3000 System with a modified recipe as our

previous reported method.[1]

In a typical process, nickel foams with a size of 8×8 cm were directly

used as the scaffold templates and were loaded into a 5 in. quartz tube inside a horizaontal tube

furnace. Then, the furnace was heated to 1000 oC under Ar (500 sccm) plus H2 (200 sccm) atmosphere

and stayed at the peak temperature for 5 min in order to clean the nickel foam surfaces and eliminate

the thin surface oxide layer. After the annealing procedure, a small amount of CH4 was introduced into

the reaction tube at ambient pressure. The flow rates of CH4, H2, and Ar were 50, 100, and 800 sccm,

respectively. After two min, Ni/GF can be obtained after being rapidly cooled to room temperature at a

rate of ~100 oC min

-1 under a constant flow of Ar (500 sccm) and H2 (200 sccm).

Synthesis of few-layer MoS2 nanosheets decorated elongated core/shell Ni3S2@MoS2 coaxial

nanofibers on Ni/graphene foam: MoS2/Ni3S2@MoS2 nanofibers were prepared using a facile one-step

hydrothermal process. In a typical experiment, the mixed solution was prepared by dissolving 150 mg

of thiourea (NH2CSNH2), 75 mg of sodium molybdate and 0.2 g of Polyvinylpyrrolidone (PVP) in 30

mL of distilled water. Then, this resulting solution was transferred into Teflon-lined stainless steel

autoclave. A piece of Ni/GF with an area of 8 cm2 was immersed into the reaction solution. The

autoclave was then sealed and the hydrothermal reaction was conducted at 200 oC for 12 h. After the

autoclave was cooled down to room temperature, the samples were rinsed with DI water for several

times and then dried in an electric oven at 60 oC for 12 h. The achieved samples were thermally

decomposed in a tube furnace at 400 oC for 2 h under H2/Ar (5:95 v/v) atmosphere with a heating rate

of 10 oC min

−1. For the comparison, the samples were prepared with the same reactant concentration at

200 oC for different reaction time.

The calculation of active materials: For MoS2/Ni3S2@MoS2 nanofibers, the total mass of the active

materials includes the mass of MoS2 and Ni3S2. The mass of Ni3S2 and MoS2 can be exactly calculated

by a FeCl3 etching method. In a typical experiment, the obtained MoS2/Ni3S2@MoS2 electrode was

immersed in a mixed solution of FeCl3 (1M) and HCl (0.5M) for 48 h. Then, the Ni foam can be

removed according to the reaction: Ni + 2FeCl3 → NiCl2+ 2FeCl2. Meanwhile, the Ni3S2 can be

oxidized to NiS2 according to the reaction: Ni3S2 + 4FeCl3 → NiS2+ 4FeCl2 + 2NiCl2, which can also

be demonstrated by the XRD patterns and TEM images of the electrode after etched in a solution of

FeCl3 (Figure S1). Therefore, the calculation of Ni3S2 and MoS2 is described as following: A circular

electrode (MoS2/Ni3S2@MoS2 nanofibers supported on Ni/GF) with a diameter of 12 mm was

immersed in a solution of 1M FeCl3 and 0.5 M HCl for 48 h. The weight decrement (x mg) can be

directly calculated by weighting the electrode before and after etched, which includes the residual Ni

foam and the loss of the element Ni from Ni3S2 to NiS2 (0.488*m(Ni3S2)). Another circular Ni/GF disk

with the same size was immersed in a mixed solution of 1M FeCl3 and 0.5M HCl for 48 h. The weight

of Ni foam (y mg) can be directly calculated by weighting the obtained sample before and after

3

reaction etched in a solution of FeCl3, which is equal to the element Ni in the electrode

(MoS2/Ni3S2@MoS2 nanofibers supported on Ni/GF), including the residual Ni foam and the element

Ni in Ni3S2 (0.732*m(Ni3S2)). Then, the mass of Ni3S2, m=(y-x) mg ×MNi3S2/MNi =(y-x) mg ×

(240/58.8) = 4.08*(y-x) mg, where M is the molecular weight or atomic weight. The mass of MoS2

can be calculated by divided the mass of Ni/GF and Ni3S2 from the mass of MoS2/Ni3S2@MoS2

nanofibers. In order to get an accurate data, we always calculated the weight of MoS2 and Ni3S2 based

on at least five sets of data.

Characterization: The X-ray powder diffraction (XRD) pattern of each sample was recorded on a

Bruke D8 Advance powder X-ray diffractometer using Cu Kα radiation (λ=0.15406 nm). Field

emission scanning electron microscopy (FESEM, Model JSM-7600F, JEOL Ltd., Tokyo, Japan) was

used to characterize the morphologies of the synthesized samples. Transmission electron microscopy

(TEM) images were taken using a JOEL JEM 2100F microscope. Raman spectroscopy was recorded

by Renishaw Raman Microscopy with 2.33 eV (532 nm) excitation laser. The Si peak at 520 cm−1

was

used as a reference to calibrate the wavenumber. The XPS measurements were performed with a VG

ESCALAB 220i-XL system using a monochromatic Al Kα1 source (1486.6 eV). All XPS spectra

were obtained in the constant pass energy (CPA) mode. The pass energy of analyser was set to be 10

eV to have high measurement accuracy. The binding energy scale was calibrated with pure Au, Ag

and Cu by setting the Au 4f7/2, Ag 3d5/2 and Cu 2p3/2 at binding energy of 84.0, 368.3 and 932.7 eV,

respectively. The surface area analysis was conducted using Brunauer-Emmett-Teller (BET) theory

(Micromeritics, ASAP 2020).

Cell Assembly and Electrochemical Measurements: To test the anode performance of all synthesised

materials, CR 2032 coin cells were assembled in an Argon-filled glovebox (Mbraun, Unilab, Germany)

with the as-fabricated MoS2/Ni3S2 hybrid electrode as the working electrode (with diameter of 12 mm,

without any binder or additives). For the fabrication of lithium ion battery, the metallic lithium foil as

the counter-electrode, 1 M LiPF6 in ethylene carbonate (EC)−dimethyl carbonate (DME) (1:1 in

volume) as the electrolyte, and a polypropylene (PP) film (Cellgard 2400) as the separator. For the

fabrication of sodium ion battery, the metallic sodium foil as the counter-electrode, 1M NaPF6 in

ethylene carbonate (EC)−diethyl carbonate (DEC)−fluoroethylene carbonate (FEC) (1:1:0.03 in

volume) as the electrolyte, and glass fiber as the separator. Galvanostatic charging and discharging

tests were conducted using a battery tester (NEWARE) at different current rates. In the measurements,

both theoretical capacities of the composites for LIBs and SIBs were regarded as 1000 mAh g-1

. Cyclic

voltammetry (CV) was performed using an electrochemical workstation (CHI 760D, Chenhua,

Shanghai) from 10 mV to 3 V at a scanning rate of 0.5 mV s-1

. Electrochemical impedance

spectroscopy (EIS) were also carried out with an electrochemical workstation over a frequency range

from 106

Hz to 100 mHz at open circuit potential after two galvanostatic charging and discharging

cycles at 100 mA g-1

.

4

Table S1 A survey of electrochemical properties of MoS2 and Ni3S2 for NIBs.

Electrode

description

1st Specific

capacity

(mAhg-1

)

1st Coulombic

efficiency

Cycling stability Rate performance

MoS2/Ni3S2@Mo

S2 coaxial

nanofiber

(This work)

1045.1 mAh g-1

at 100 mA g-1

77%

462 and 330.8 mA

g−1

after 400

cycles at current

densities of 2 and

5 A g-1

856.8, 778.4, 722.1,

647.1, 578.2, 507.4

and 429.5 mAh g−1

at 100, 200, 500,

1000, 2000, 3000

and 5000 mA g−1

.

MoS2/graphene

paper [1]

520 mAh g-1

at 25 mA g-1

46.2%

218 mAh g-1

after

20 cycles at 25

mA g-1

240 and 214 mAh

g-1

at 25 and 100

mA g-1

MoS2

nanoflowers [2]

243 mAh g-1

at 200 mA g-1

88%

350 mAh g-1

at 50

mA g-1

, 300 mAh

g-1

at 1 A g-1

and

195 mAh g-1

at 10

A g-1

after 20

cycles

200 and 175 mAh

g-1

at 1 and 10 A g-1

MoS2 nanosheets [3]

998 mAh g-1

at 200 mA g-1

41%

386 mA h g-1

at 50

mA g-1

after 100

cycles

350 mA h g-1

at 80

mA g-1

, 305 mA h

g-1

at 160 mA g-1

,

and 251 mA h g-1

at

320 mA g-1

MoS2-graphene

microspheres [4]

797 mAh g-1

at 200 mA g-1

72%

480 mA h g-1

at

200 mA g-1

after

50 cycles

427, 355, 306, 273,

and 234 mA h g-1

at

1, 3, 5, 7 and 10 A

g-1

TiO2@MoS2

nanofibers [5]

985 mAh g-1

at 100 mA g-1

73%

474 mA h g-1

at

100 mA g-1

after

30 cycles

600 mA h g-1

even

at 5 C

MoS2/C

nanospheres [6]

1500 mAh g-1

at

100 mA g-1

44.7%

520 mA h g-1

at

100 mA g-1

after

50 cycles

390 mA h g-1

even

at 2 C

MoS2 embedded

in carbon

nanfibers [7]

854 mAh g-1

at 100 mA g-1

52%

484 and 253 mA h

g-1

at 1 and 10 A

g-1

after 100 cycles

854, 700, 623, 436,

331, 224, 155, and

75 mAh g-1

for

current densities of

0.1, 0.5, 1, 5, 10, 20,

30, and

50 A g-1

MoS2/C

nanofibers [8]

471.2 mAh g

-1

at 100 mA g-1

81.2%

283.9 mA h g-1

at

100 mA g-1

after

600 cycles

283.3, 246.5 and

186.3 mA h g-1

at

0.5, 1 and 2 A g-1

MoS2/graphene

composite [9]

1680 mAh g

-1

at 20 mA g-1

47.6%

340 mA h g-1

at 20

mA g-1

after 100

cycles

MoS2/graphene

microspheres [10]

640 mAh g

-1

at 100 mA g-1

62.5%

340 mAh g-1

at 100 mA g-1

after

50 cycles

230 mA h g-1

at 5 A

g-1

Ni3S2-PEDOT [11]

458 mAh g-1

at 100 mA g-1

83.6%

400 mAh g−1

after

50 cycles at

600mAg−1

600, 503, 408 and

310 mAh g-1

at 150,

300, 600 and 1200

5

mA g-1

Ball-milling of

Ni3S2 powders [12]

420 mAh g-1

at

100 mA g-1

89.5%

342 mAh g−1

after

150 cycles at

100mAg−1

6

Figure S1 (a) XRD patterns, (b) and (c) SEM images, and (d)-(f) TEM images of

Ni3S2@MoS2 electrode after etched in a FeCl3 solution.

10 20 30 40 50 602(deg)

Inte

nsit

y (

a.u

.)

MoS2

CNiS2(a)

(d)

(b) (c)

(e) (f)

1 μm 100 nm

0.69 nm

20 nm 10 nm 1 nm

MoS2 belt

0.27 nm(100)MoS2

7

Figure S2 (a) XRD patterns and (b) Raman spectra of MoS2/Ni3S2 and Ni3S2@MoS2. FESEM

images of (c) MoS2/Ni3S2 and (d) Ni3S2@MoS2

500 1000 1500 2000 2500 3000 3500

Ni3S2Ni3S2

2DG

D

MoS2

Raman Shift (cm-1)

In

ten

sit

y (

a.u

.)

MoS2@Ni3S2

MoS2/Ni3S2

10 20 30 40 50 60 70 802(deg)

Inte

nsit

y (

a.u

.)

MoS2

C

MoS2/Ni3S2

MoS2@Ni3S2

Ni3S2Ni

10 20 30 40 502(deg)

Inte

ns

ity

(a

.u.)

(a) (b)

200 nm

(d)

100 nm

(c)

8

Figure S3 (a) Charge and discharge curves and (b) cycling behavior of pure GF as anode of

SIBs at a current density of 200 mAh g–1

.

0 5 10 15 20 25 30 35

0.5

1.0

1.5

2.0

2.5

3.0 1st

2nd

3rd

(a)

Specific Capacity (mAh g-1

)

Po

ten

tia

l (V

vs.

Na )

0 50 100 150 200

0

5

10

15

20

25

30

35

Cap

acit

y (

mA

h g

-1)

Cycle number

(b)

9

Figure S4 Nyquist plots of MoS2/Ni3S2@MoS2 electrode during 400 charge/discharge cycle

at different cycles. The resistance is simulated using the inset of equivalent circuit model.

0 100 200 300 400

0

100

200

300

400

500

Z' (ohm)

-Z''

(oh

m)

Fresh cell

50 cycle

100 cycle

200 cycle

300 cycle

400 cycle

Rsf

CPE2

WRct

CPE1Ri

10

Figure S5 (a), (b) Representative photograph showing the dimension and flexibility of the

MoS2/Ni3S2@MoS2 electrode. (c) Optical images of the flexible poach SIB. (d) The voltmeter

of the flexible SIB when flat, after flexing once and after flexing for 30 cycles.

Flat After 1 flex cycle After 30 flex cycle Flat after 30 flex cycle

(a) (b) (c)

(d)

Flat After 1 flex cycle After 30 flex cycle Flat after 30 flex cycleFlat After 1 flex cycle After 30 flex cycle Flat after 30 flex cycle

11

Figure S6 SEM images of MoS2/Ni3S2 electrode as anode of SIBs after long-term cycles.

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(a) (b)

10 μm 1 μm