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Supporting InformationFast Electrochemical Kinetics and Strong Polysulfide Adsorption by Highly-Oriented

MoS2 Nanosheets@N-Doped Carbon Interlayer for Lithium-Sulfur Batteries

Jingyi Wu, Xiongwei Li, Hongxia Zeng, Yang Xue, Fangyan Chen, Zhigang Xue, Yunsheng

Ye*, Xiaolin Xie*

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

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Li+ diffusion coefficients (DLi+) were calculated from the linear fitting of the peak current

versus the square root of the scan rate using cyclic voltammetry (CV) scans at various scan

rates from 0.1 to 0.5 mV s-1 by the Randles-Sevcik equation:

(1)𝐼𝑝= 2.69 × 10

5𝑛32𝐴𝐷

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𝐿𝑖+𝐶𝐿𝑖+

𝑣12

Where (A) is the peak current, n is the number of electrons transferred in the reaction (n=2 𝐼𝑝

for Li-S batteries), A (cm2) is the electrode area (A=2.01 cm2), (cm2 s-1) is the Li-ion 𝐷𝐿𝑖+

diffusion coefficient, (mol mL-1) is the concentration of Li-ion ( =110-3 mol mL-1), 𝐶𝐿𝑖+

𝐶𝐿𝑖+

and (V s-1) refers to the scan rate. 𝑣

The binding energy (Ebinding) between MoS2 and Li2S4 in DFT calculation is defined as

Ebinding = EMoS2 + ELi2S4 – E MoS2+Li2S4 (2)

where EMoS2, ELi2S4 and EMoS2+Li2S4 are the energy of MoS2, Li2S4, and MoS2 with the adsorbed

Li2S4.

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Fig. S1 TEM image of 3D MoS2.

Fig. S2 Raman spectra of the bulk MoS2.

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Fig. S3 N2 adsorption-desorption isotherms and the pore-size distribution (inset) of

MoS2@NC.

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Fig. S4 (a) XPS survey, (b) Mo 3d and (c) S 2p spectra of MoS2@NC.

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Fig. S5 S 2p XPS of MoS2@NC after polysulfide adsorption.

Fig. S6 Optimized configurations of Li2S4 and MoS2 basal plane (a) and Mo-edge (b) by DFT

calculations.

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Fig. S7 Polysulfide adsorption experiments of NCS, MoS2+NCS, MoS2@NC, and MoS2.

Fig. S8 The optical image of the MoS2@NC interlayer coated sulfur cathode.

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Fig. S9 TEM images of NCS.

Fig. S10 (a) The first four CV scans at a scan rate of 0.2 mV s-1 and (b) CV curves at scan rates

ranging from 0.1 to 0.5 mV s-1 of the cell with the MoS2@NC interlayer

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Fig. S11 Galvanostatic charge-discharge voltage profiles of the cell with the MoS2@NC

interlayer during the initial 10 cycles at 0.5 C.

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Fig. S12 CV curves at scan rates ranging from 0.1 to 0.5 mV s-1 and the corresponding linear

fitting of the peak currents vs. the square root of the scan rates of the cell with (a, b) the

MoS2@NC interlayer, (c, d) no interlayer.

CV curves of the cell with the MoS2@NC interlayer process three interesting features: (i) a

shoulder peak at ~ 2.40 V under low scan rates (0.1 and 0.2 mV s-1) indicating the step-wise

oxidation of Li2S2/Li2S to Li2Sx (4 ≤ x ≤ 8) and then to S8 with the help of MoS2@NC; (ii) a

clear separation between peak A and B suggesting stronger polysulfide trapping ability; (iii)

the narrower peaks and the lower polarization indicating faster polysulfide reduction kinetics.

Fig. S13 Cycling performance of Li-S cells with MoS2 and NCS interlayers at 0.5 C

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Fig. S14 (a) QHigh retention, (b) QLow retention and (c) the capacity ratio (QLow/QHigh) of cells

with the MoS2@NC interlayer and the MoS2+NCS interlayer at 0.5 C.

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Fig. S15 Cycling performance at 1 C of different cells.

Fig. S16 The capacity ratio (QLow/QHigh) at current rates from 0.1 to 2 C.

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Fig. S17 Charge-discharge profiles at a sulfur loading of 4.0 mg cm-2 of the cells with (a) the

MoS2@NC interlayer and (b) no interlayer.

Fig. S18 Rate performance at a sulfur loading of 4.0 mg cm-2, based on the mass of sulfur

(black), the total mass of cathode (blue) and the combined mass of cathode and MoS2@NC

interlayer (red).

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Fig. S19 S 2p XPS of the unwashed Li anodes extracted after 100 cycles from the cell with the

MoS2@NC interlayer (a), the MoS2+NCS interlayer (b) and without any interlayer (c).

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Fig. S20 Photographs of the separators extracted from cells after 100 cycles with the

MoS2@NC interlayer (a), the MoS2+NCS interlayer (b) and no interlayer (c).

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Table S1 Li+ diffusion coefficients calculated from the Randles-Sevcik equation of cells with

different configurations.

sample DLi+ at peak A

(cm2 s-1)

DLi+ at peak B

(cm2 s-1)

DLi+ at peak C

(cm2 s-1)

MoS2@NC 8.10ⅹ10-9 2.66ⅹ10-8 4.28ⅹ10-8

Celgard 4.35ⅹ10-9 9.69ⅹ10-9 1.79ⅹ10-8

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Table S2 Comparison of the electrochemical performance in Li-S batteries with metal

compound interlayers in recent publications.

Interlayer Cathode C-rate Initial Discharge Capacity(mAh g-1)

Capacity decay (% per cycle)

High RatePerformance

Year [ref]

MoS2@NC S-CB 2 885 0.034 (1500th)

876 (3 C) This work

MoS2/rGO S-CB 1 877 0.116 (500th) 615 (2 C) 20181

MoS2/CNT S/CNT - - - (500th) 650 (2 C) 20172

MoS2 S-CB 0.5 808 0.083 (600th) 550 (1 C) 20173

Sb3S2/CNT S-CB 1 750 0.049 (1000th)

530 (2 C) 20184

Laponite/CB S-CB 1 881 0.028 (500th) 758 (2 C) 20185

NbC Sulfur composite

2 1120 0.037 (1500th)

730 (5 C) 20186

LiF/GO Carbon/S 2 721 0.043 (400th) 524 (3 C) 20187

WS2/Carbon cloth

WS2/S/CB 0.5 1400 0.055 (500th) 702 (5 C) 20178

CNT@TiO2 S-CB 1 1190 0.056 (1000th)

740 (2 C) 20179

CNT@V2O5 S-CB 3 816 0.03 (1000th) 709 (5 C) 201710

Hollow CF@-MnO2

S-CB 0.5 - - (200th)

554 (2 C) 201711

“-”: data not available; CB: carbon black; rGO: reduced graphene oxide; CNT: carbon nanotube; GO: graphene oxide; CF: carbon fiber.

Table S3. The fitting data of S 2p XPS of the unwashed Li anodes extracted from different

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cells after 100 cycles.

MoS2@NC interlayerPeak Position (eV) Area FWHM (eV) Total Area1 169.78 935.57 2.302 167.37 230.20 1.45

1165.77

3 164.52 96.15 2.004 163.43 61.38 1.035 162.45 40.03 0.75

197.56

MoS2+NCS interlayerPeak Position (eV) Area FWHM (eV) Total Area1 169.78 1105.89 2.582 167.12 286.79 1.86

1392.68

3 164.15 80.20 1.304 163.30 100.71 1.125 162.10 137.01 1.14

317.92

Without any interlayerPeak Position (eV) Area FWHM (eV) Total Area1 169.51 942.16 2.492 167.14 453.10 1.56

1395.26

3 164.01 190.29 1.684 163.04 131.45 1.065 162.23 142.97 1.04

464.71

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