1

Supplementary Figure 1. Element analysis in electrode. Electron energy loss spectrum for SG-Si

electrode after sluggish heat treatment (SHT).

2

Supplementary Figure 2. Structure changes of PAN before and after SHT. (a) Differential scanning

calorimetry (DSC) for polyacrylonitrile (PAN) in nitrogen showing a characteristic peak at ~ 300oC,

which corresponds to PAN cyclization as proposed in (d); (b) Thermogravimetric analysis for PAN in

both air and in nitrogen. During cyclization in nitrogen there is more loss in mass which reveals it is more

efficient than in air. By cyclization PAN loses ~ 20% of its mass, (c) Nitrogen high resolution XPS of

SG-Si-PAN (before SHT), and SG-Si-C_PAN (after SHT)

50 100 150 200 250 300 350-5

0

5

10

15

20

Heat

Flo

w, m

W

Temperature, oC

100 200 300 40050

60

70

80

90

100

110

We

igh

t lo

ss

, %

Temperature, oC

N2

Air

PAN

c-PAN406 404 402 400 398 396

SG-Si-C_PAN

Inte

nsit

y,

a.u

.

Binding Energy, eV

SG-Si-PAN

a b

c d

3

Supplementary Figure 3. Effect of annealing PAN on resistance. Electrochemical impedance for a

coin cell fabricated using PAN-coated copper foil vs lithium, same method of cell testing as described in

the experimental section. The figure reveals that both the electrode series resistance and the charge

transfer resistance have been decreased after the sluggish heat treatment.

0 500 1000 1500 20000

500

1000

1500

2000

PAN-b

efore

SHT

Zim

, o

hm

s

Zre, ohms

PAN-a

fter

SHT

4

Supplementary Figure 4. Morphology of the electrode. (a) TEM image of SG-Si electrode material, (b-

f) the corresponding EDX mapping of the elements carbon, oxygen, silicon, sulfur, and nitrogen,

respectively, and (g) overlaid colour map of carbon (green), silicon (red), and sulfur (blue).

5

Supplementary Figure 5. Sulfur distribution on SG nanosheet. (a) STEM-HAADF of a SG

nanosheet in a micron size, (b) and (c) are the EDX mapping for sulfur and carbon, respectively;

(d) is the electron energy loss spectroscopy (EELS) mapping and € represent the EELS mapping

of sulfur in pixilated grey color, each pixel represent 10 x 10 nm. The figure clearly prove the

doping with sulfur in the bulk of SG nanosheet as well as on the edges.

a

b c

d e

6

Supplementary Figure 6. Morphology of SG-Si-PAN electrode. (a) The as-prepared electrode after

drying, (b) The electrode after sluggish heat treatment, and (c) The electrode extracted from a coin cell

which was cycled for 100 cycles.

SHT treatment at

450oC

SG-Si-PAN electrodeSG-Si-c_PAN electrode

After cycling in a coin cell

a b

c

7

0 50 100 150 200 250

0.00

0.05

0.10

0.15

0.20

0.25

electrode before SHT

(dV

/dlo

g(D

) P

ore

Vo

lum

e (

cm

³/g

)

Pore Diameter (nm)

electrode after SHT

Supplementary Figure 7. Porosity in the electrode. Comparison of pore size distribution for the SG-Si

electrode before and after SHT. The pore volume increases after SHT which provide void space that

compensate the volume expansion of Si during lithiation.

8

Supplementary Figure 8. Cyclic voltammogram curves of G-Si anode material in coin cell.

Supplementary Figure 9. Cycle stability of a reference cell. The cell was fabricated using SiNP (60%),

PVDF (20%) as binder, and super P (20%) as conducting carbon, the performance was tested at 0.1Ag-1

.

2 4 6 8 10 12 14 16 18 200

1000

2000

3000

4000

5000

Sp

ecif

ic c

ap

acit

y (

mA

h/g

)

Cycle No.

0

20

40

60

80

100

Eff

icie

ncy (

%)

0.0 0.3 0.6 0.9 1.2 1.5

-0.4

-0.2

0.0

0.2

0.4

Cu

rren

t d

ensi

ty, A

g-1

Potential, V vs. Li/Li+

1st cycle

2nd cycle

3rd cycle

4th cycle

5th cycle

9

Supplementary Figure 10. Reference battery testing. (a) SG-PAN, and (b) only c-PAN, after being

subjected to SHT treatment. The cells were tested at 0.1A g-1

then continued at 2 A g-1

. The SG-PAN

provide reversible capacity of ~ 250 mAh g-1

and the c-PAN provide ~ 25 mAh g-1

.

0 200 400 600 800 10000

50

100

150

200

Sp

ec

ific

Ca

pa

cit

y,

mA

h g

-1

Cycle No.

0 20 40 60 80 100 120 1400

200

400

600

800

Sp

ec

ific

Ca

pa

cit

y,

mA

h g

-1

Cycle No.

discharge

charge

0

20

40

60

80

100

Eff

icie

nc

y,

%

a

b

10

Supplementary Figure 11. Cycling performance for reference batteries. These were fabricated using

SG + SiNP + PVDF with no SHT treatment. (a) The cell subjected to rate capability at different current

then continued at 2 A g-1

. (b) The cell was tested at 0.1 A g-1

for 5 cycles then continued at 2 A g-1

for the

rest.

Supplementary Figure 12. Cycling performance for reference batteries. These were fabricated using

SiNP + Graphene oxide + PAN with SHT treatment. (a) The cell subjected to rate capability at different

current then continued at 2 A g-1

. (b) The cell was tested at 0.1 A g-1

for 5 cycles then continued at 2 A g-1

for the rest.

0 20 40 60 80 100 120 140 160 180

0

500

1000

1500

2000

2500

3000

3500

Sp

ecific

ca

pa

city (

mA

h g

-1)

Cycle (No.)

Charge

Discharge

2A/g

0.1A/g-->0.5A/g-->1.0A/g-->2.0A/g-->A/g4.0-->2.0A/g

0 20 40 60 80 100 120 140 160 180 200

0

500

1000

1500

2000

2500

3000

3500

Sp

ecific

ca

pa

city (

mA

h g

-1)

Cycle (No.)

Charge

Discharge

2A/g

0.1A/g

(a) (b)

30 60 90 120 150 180

0

500

1000

1500

2000

2500

3000

3500

4000

2 A/g

Sp

ecific

ca

pa

city (

mA

h g

-1)

Cycle (No.)

Charge

Discharge0.1 A/g

0 10 20 30 40 50 60 70 80 90

500

1000

1500

2000

2500

3000

3500

4000

2 A/g

0.1A/g-->0.5A/g-->1A/g-->2A/g-->4A/g-->2A/g

Sp

ecific

ca

pa

city (

mA

h g

-1)

Cycle (No.)

Charge

Discharge

0.1 A/g

(a) (b)

11

0 20 40 60 80 1000

500

1000

1500

2000

2500

3000

Vo

lum

etr

ic C

ap

acity, m

Ah

cm

-3

Cycle No.

Charge

Discharge

Supplementary Figure 13. Volumetric Capacity. The data presented here is for SG-Si-c-PAN electrode

for the cell performance with data shown in Figure 4b.

12

Supplementary Figure 14. Further battery performance. The results presented here is for SG-Si-c-

PAN electrode with ratio of 40:30:30, respectively. (a) The cell cycled at 0.1 A g-1

for conditioning then

continued at 1 A g-1

. (b) The cell started conditioning cycles then continued with rate capability at

different currents then continued cycling at 2 A g-1

. N.B. The Capacity measured here is per mass of

silicon and SG.

0 20 40 60 80 1000

1000

2000

3000

4000

Charge

Discharge

Efficiency

Sp

ecific

Ca

pa

city (

mA

h/g

)

Cycle number

0.1 A/g

1 A/g

0

20

40

60

80

100

Eff

icie

ncy (

%)

Si-SG-c_PAN 40:30:30

0 25 50 75 100 125 150 175 200 225 250

0

1000

2000

3000

4000

2 A/g

4 A

/g

3 A

/g2 A

/g

1.5

A/g

1 A

/g

0.5

A/g

Charge

Discharge

Efficiency

Sp

ec

ific

Ca

pa

cit

y (

mA

h/g

)

Cycle number

0.1

A/g

0

20

40

60

80

100

Eff

icie

nc

y (

%)

Si-SG-c_PAN 40:30:30

a

b

13

Supplementary Figure 15. After cycling characterization of SG-Si. (a) STEM image of SG-Si

electrode material after being cycled for 2275 cycles of charge discharge, b-f) the corresponding EDX

mapping of the elements carbon, oxygen, silicon, sulfur, and nitrogen, respectively.

Supplementary Figure 16. After cycling characterization of G-Si. The figure shows HAADF-STEM

image of the G-Si electrode after cycling for 800 cycles as shown in Figure 5e, it shows the

agglomeration of Si which explain the capacity fading.

14

Supplementary Figure 17. The optimized geometry of H passivated graphene (G). Top view (top)

and side view (bottom). C atoms are colored grey, H atoms white. Bond length is in angstrom.

15

Supplementary Figure 18. The optimized geometry of sulfur-doped graphene (S-G). top view (top)

and side view (bottom). C atoms are colored grey, H atoms are white, S atom is yellow. Bond lengths are

in angstrom.

16

Supplementary Figure 19. Geometries and bonding energy (BE) of the stable Si4 cluster adsorption

configurations. (a) On graphene, (b) On sulfur doped graphene. C atoms are colored grey, H atoms are

white, S atom is yellow, Si atoms are brown.

17

Supplementary Figure 20. Li adsorption and transition state. The figure quantifies Li diffusion barrier

for a) G-Si and b) SG-Si