Supporting Information

High-performance 3 V “water in salt” aqueous asymmetric

supercapacitors based on VN nanowires electrode

Mingyu Ma1, Zude Shi1, Yan Li1, Yifan Yang1, Yaxiong Zhang1, Yin Wu1, Hao Zhao2, and Erqing Xie1*

Affiliations1. School of Physical Science & Technology, Lanzhou University, Lanzhou, 730000, China.2. School of Science and Technology for Opto-Electronic Information, Yantai University, Yantai, Shandong 264005, China.* Corresponding author: xieeq@lzu.edu.cn.

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2020

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0-250-200-150-100

-500

50100150200250

Spe

cific

cap

acita

nce

(F g

-1)

Potential (V vs. Ag/AgCl)

-1.2-0.7 -1.3-0.7 -1.4-0.7 -1.5-0.7 -1.6-0.7 -1.7-0.7 -1.8-0.7

20 mV s-1

Figure S1. the CV curves of VN-NWs@CC in 21 m LITFSI aquesou electrolyte at

different potential ranges

a b

Figure S2. The SEM images of magnification of (a) 100000× and (b) 167869 × for the

α-Fe2O3 materials.

-1.5 -1.0 -0.5 0.0 0.5 1.0-8

-6

-4

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0

2

4

6

0.5 V

0.7 V

Cur

rent

(mA

)

Potential (V vs. Ag/AgCl)

VN α-Fe2O3 Carbon cloth

-1.4 V

-1.2 V

Figure S3. The CV curves of VN, α-Fe2O3, and Carbon cloth electrode in 21m LITFSI

electrolyte at a scan rate of 20 mV s-1.

0.0 0.5 1.0 1.5 2.0 2.5-4.0

-3.5

-3.0

-2.5

-2.0

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-1.0

Log

i (Pe

ak c

urre

nt, m

A)

Log (Scan rate, mV s-1)

Cathodic peak Anodic peak b=0.96 b=0.95

-1.0 -0.8 -0.6 -0.4 -0.2 0.0-400-300-200-100

0100200300400

Spe

cific

cap

acita

nce

(F g

-1)

Potential (V vs. Hg/HgO)

2 mV s-1 5 mV s-1 10 mV s-1

20 mV s-1 50 mV s-1 100 mV s-1a b

Figure S4. (a) CV curves of VN-NWs@CC at various scan rates in aqueous electrolyte;

(b) b-value analysis using the relationship between the peak currents and the scan rates.

0 2000 4000 6000 8000 100000

20

40

60

80

Spe

cific

cap

acita

nce

(F g

-1)

Cycle number

71.3 F g-1

47.8 F g-1

0

20

40

60

80

100

Cou

lom

bic

effic

ienc

y (%

)

0 2000 4000 6000 8000100000

20

40

60

80

100

Spe

cific

cap

acita

nce

(F g

-1)

Cycle number

1M KOH 7.29%

69.59 F g-1

5.07 F g-1

0

20

40

60

80

100

120

Cou

lom

bic

effic

ienc

y (%

)

10 20 30 40 50 60 70 80 90

After 10000 cycles

PDF#65-7326-VN

Inte

nsity

(a.u

.)

2 Theta (degree)

Pristine

After 2000 cycles

a b

395 396 397 398 399 400 401 402

Inte

nsity

(a.u

.)

Binding energy (eV)

N 1sAfter 10000 cycles

After 2000 cycles

Pristine

c d

Figure S5. The cycling performance of VN-NWs@CC electrode for 10,000

charge/discharge tests (a) in 1M KOH electrolyte at a current density of 20 A g-1, (b) in

21 m LITFSI electrolyte at a current density of 5 A g-1, (c) the high-resolution XPS

spectra of N 1s and (d) XRD patterns for pristine VN, after 2000 cycles, and after 10000

cycles in 21 m LITFSI electrolyte.

a b

dc

Figure S6. (a) The XPS spectra of full spectrum, high-resolution (b) C 1s, (c) N 1s, and

(d) O 1s at pristine, full charge, and full discharge state.

Figure S7. The high-resolution TEM image of VN-NWs@CC of full-discharged state.

0.3 0.6 0.9 1.2 1.5 1.8 2.1

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0

200

400

600S

peci

fic c

apac

itanc

e (F

g-1)

Potential (V vs. Ag/AgCl)

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0

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Spe

cific

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(F g

-1)

Current density (A g-1)

a b

Figure S8. (a) The CV curves of VN-NWs@CC in 21 m LITFSI aquesou electrolyte at

different potential ranges, (b) the specific capacitance as a function of current densities

for the MnO2 electrode at 21m LITFSI electrolyte.

Table S1. The comparison of fiting result derived from the impedance spectra with EIS

analysis.

Samples VN α-Fe2O3 Carbon cloth

Rs (ohm) 5.975 6.142 5.523

Rct (ohm) 10.09 9.95 10.02

CPEEDL (S secn) 2.89×10-7 6.91×10-7 5.11×10-7

nEDL 0.9682 0.9279 0.9172

CPEP (S secn) 0.1067 0.0025 0.0069

nP 0.9878 0.8683 0.7879

Zw (ohm sec-1/2) 6.96 11.50 17.45

The Rs refers to resistance of electrode and electrolyte, Rct refers to the charge-transfer

resistance, Zw is Warburg impedance corresponding to semi-finite diffusion, and CPE

is the constant phase element.

Table S2. The comparison of Warburg coefficient (σ), and chemical diffusion

coefficient (D) for VN, α-Fe2O3, and Carbon cloth samples, respectively.

Samples σ (ohm s-1/2) D (cm2 s-1)

VN 15.17 5.20×10-14

α-Fe2O3 32.20 3.17×10-14

Carbon cloth 36.40 3.07×10-15