Supporting Information

Electrospun Li3V2(PO4)3 nanocubes/carbon nanofibers as free-

standing cathodes for high-performance lithium-ion batteries

Yi Peng,a Rou Tan, a Jianmin Ma,b Qiuhong Li, Taihong Wang,a and Xiaochuan

Duan*a

a Pen-Tung Sah Institute of Micro-Nano Science and Technology, Xiamen University,

Xiamen, 361005, PR China.

b School of Physics and Electronics, Hunan University, Changsha, 410082, PR China.

Corresponding author: Prof. Xiaochuan Duan, Email: xcduan@xmu.edu.cn

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2019

S1. Results and Discussion

Figure S1. Digital photographs of the preparation process of LVP-NC/NCNF free-

standing electrodes using an IL-assisted electrospinning method: (a) the nanofiber

membrane after electrospinning process; (b) the free-standing membrane after

calcination; (c, d) the circular free-standing electrodes with a diameter of 12 mm

prepared by a punching machine; (e) the as-prepared free-standing electrode can be

easily bent, showing its good mechanical property.

Figure S2. XRD pattern and Rietveld refinement of the as-prepared LVP-NC/NCNF

free-standing electrodes.

800 700 600 500 400 300 200 100

Inte

nsity

(a.u

.)

Binding energy (eV)

O1s

V2pN1s

C1s

P2s P2p

Figure S3. The wide XPS survey spectrum of the LVP-NC/NCNF free-standing

electrodes.

Figure S4. The low-magnification TEM images of the obtained LVP-NC/NCNF

sample.

0.0 0.2 0.4 0.6 0.8 1.0

0

20

40

60

80

100

120

140

Volu

me

adso

rbed

(cm

3 g-

1 , S

TP)

Relative pressure (P/P0)

LVP-NC/NCNF LVP-NP/CNF LVP-NP

Figure S5. Nitrogen adsorption/desorption isotherms of the as-prepared LVP-

NC/NCNF, LVP-NP/CNF, and LVP-NP samples. The BET surface area of LVP-

NC/NCNF is about 247.1 m2∙g-1, which is much higher than that of LVP-NP/CNF

(32.2 m2∙g-1) and LVP-NP (19.9 m2∙g-1).

Figure S6. (a) Temperature-dependent XRD patterns of the samples obtained from

500 oC to 800 oC. (b) SEM images of the samples obtained from 500 oC to 800 oC.

The scale bar is 1 μm. (c) FT-IR spectra of IL ([Bmim]H2PO4), IL-LVP/CNF, pure

LVP and PAN, respectively.

Figure S7. (a) TGA curve of LVP-NC/NCNF precursor under N2 atmosphere. (b)

TGA curve of LVP-NC/NCNF under air.

Figure S8. Representative phases and morphologies of the contrastive LVP-NP/CNF

and LVP-NP samples: (a) XRD pattern, (b) low-magnification and (c) high-

magnification SEM images of LVP-NP/CNF; (d) XRD pattern, (e) low-magnification

and (f) high-magnification SEM images of LVP-NP.

Figure S9. (a) Low-magnification and (b) high-magnification SEM images of the

LVP-NC/NCNF free-standing electrode after 1750 cycles at 1C.

Figure S10. The adopted quivalent circuit model for EIS analysis.

The calculation of lithium ion diffusion coefficient: In order to investigate the

electrochemical kinetics features of LVP-NC/NCNF, LVP-NP/CNF and LVP-NP,

EIS and CV measurements were both carried out. As shown in Figure 4a, all the EIS

curves contain a semicircle in the high-frequency region and a sloping straight line in

the low-frequency region, which corresponding to the charge transfer resistance (Rct)

between the electrode/electrolyte interfaces and the Warburg impedence (Zw) related

to the Li+ diffusion. According to the simulating results (Table S2) obtained by an

equivalent circuit using the Zview software, the charge transfer resistance (Rct) of

LVP-NC/NCNF (46.7 Ω) is much smaller than those of LVP-NP/CNF (113 Ω ) and

LVP-NP (210.3 Ω ), which demonstrating that the ILP enhances the conductivity of

LVP. What’s more, the Li+ diffusion coefficient can be calculated from the low

frequency plots by the following equation:

DLi+ = R2T2/2A2n4F4C22

where R is gas constant (8.314 Jmol-1K-1), T is absolute temperature (298.15 K), A is

the surface area (1.13 cm2), n is the number of electrons of per molecule during

oxidation (n = 1), F is faraday constant (96485 C mol-1), C is the concentration of

lithium ions in the electrode material (1×10-3 mol cm-3) and is Warburg factor

which is related to Z and -1/2 through the following formula:

Z = Rs + Rct + -1/2

Figure 4b displays the relationship between Z and -1/2 in the low frequency region.

As a result of calculation in Table S2, LVP-NC/NCNF exhibites the lowest Warburg

factor and the highest lithium ion diffusivity followed by LVP-NP/CNF and LVP-NP

in sequence, confirming that the ILP facilitates the Li+ diffusion kinetics, which

leads to an excellent rate property.

The CV curves of LVP-NC/NCNF at various scanning rates between 3.0 V and

4.3 V are displayed in Figure 4c. There are three couples of redox peaks (marked as

a1/a2, b1/b2, c1/c2 in turn) in each CV profile, representing the extraction/reinsertion of

two Li+ in Li3V2(PO4)3 by three steps. According to the Randles Sevchik equation:

Ip = 2.69 105 n3/2A DLi+1/2 1/2C

where Ip is the peak current (A), is the scanning rate (V/s), and the increase of Ip is

proportional to the rise of . According to the fitting slope of Ip vesus 1/2 plot (Figure

4d), the Li+ diffusion coefficients are calculated and listed in Table S3. Obviously, the

DLi+ value of peak c1 is the highest among all the oxidation peaks. Similarly, DLi+ of

peak c2 is the highest among all the reduction peaks, illustrating that the process of

Li3V2(PO4)3 transforming into Li2.5V2(PO4)3 phase is the most difficult kinetics

among the three steps.

S2. Tables

Table S1. Elemental analysis of the as-prepared IL-NC/NCNF, LVP-NP/CNF and

LVP-NP samples.

Sample C (wt%) N (wt%) H (wt%)IL-NC/NCNF 45.96 5.478 1.318LVP-NP/CNF 4.967 0.456 0.261

LVP-NP 0.523 0.455 0.158

Table S2. Simulated impendence parameters (Rs, Rct), calculated Warburg factor (σ)

and lithium ion diffusion coefficients of the LVP-NC/NCNF, LVP-NP/CNF and

LVP-NP samples obtained from EIS plots.

Samples Rs () Rct () cm2 s-1/2) DLi+ (cm2 s-1)

LVP-NC/NCNF 5.87 46.7 39.03 10-11

LVP-NP/CNF 6.78 113 282.22 3.49 10-13

LVP-NP 9.23 210.3 437.95 1.45 10-13

Table S3. Lithium ion diffusion coefficients at each stage for the LVP-NC/NCNF

sample obtained from CV curves.

LVP-NC/NCNF peak DLi+ (cm2 s-1)

peak a1 2.60 10-9

peak b1 4.61 10-9Oxidation

peak c1 1.05 10-8

peak a2 2.27 10-9

peak b2 3.61 10-9Reduction

peak c2 7.30 10-9

Table S4. Summary of the preparation and electrochemical performance of LVP-based cathodes with different structures.

Materials MethodsSpecific capacity

[mAh g-1]Rate performance and

Cycle stability [mAh g-1]Ref.

LVP/C@NCF

Ball milling &slurry infiltration

122.1 at 0.5C102.5 mAh∙g-1

after 1000 cycles at 10C[1]

LVP/C-NWs

Hydrothermal 128 at 0.5C96 mAh∙g-1

after 3000 cycles at 5C[2]

LVP/C Sol-gel 119 at 0.5C105.6 mAh∙g-1

after 400 cycles at 5C[3]

LVP/CNF Electrospinning 126 at 0.1C119.5 mAh∙g-1

after 500 cycles at 1C[4]

LVP/CNFSol-gel&

Electrospinning&CVD

128 at 0.5C120.6 mAh∙g-1

after 500 cycles at 5C[5]

LVP/C-S Sol-gel&Doping 127.4 at 1C113.7 mAh∙g-1

after 300 cycles at 5C[6]

LVP/C Sol-gel 120 at 1C102.6 mAh∙g-1

after 100 cycles at 10C[7]

LVP/CNT Sol-gel 118.52 at 1C106.4 mAh∙g-1

after 200 cycles at 5C[8]

LVP/C Sol-gel 131 at 1C122.5 mAh∙g-1

after 100 cycles at 10C[9]

LVP/C Hydrothermal 128 at 1C112.5 mAh∙g-1

after 1000 cycles at 5C[10]

LVP-NC/NCNF

IL-assisted electrospinning

148.3 at 0.5C143.6 mAh∙g-1

after 1000 cycles at 5CThis work

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