Supporting Information

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S1

Supporting Information

CoS

2

-Decorated Cobalt/Nitrogen Co-Doped Carbon Nanofiber

Networks as Dual Functional Electrocatalysts for Enhancing

Electrochemical Redox Kinetics in Lithium-Sulfur Batteries

Shanshan Yao*, †_{Cuijuan Zhang}†_{, Ruiduo Guo}†_{, Arslan Majeed}†_{, Yanping He}†_,

Youqiang Wang†_{, Xiangqian Shen}†, ‡_{, Tianbao Li}‡_{, Shibiao Qin}‡

†_{Institute for Advanced Materials, College of Materials Science and Engineering,}

Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, P. R. China

‡_{Hunan Engineering Laboratory of Power Battery Cathode Materials, Changsha}

Research Institute of Mining and Metallurgy, 966 Lushan South Road, Changsha 410012, P. R. China

Corresponding author: Shanshan Yao ([email protected])

Number of Pages: 11

Number of Tables: 2 (Table S1 and S2)

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S2

Synthesis of CSCNC @Li2S6 electrode

The blank electrolyte was composed of 1M bis(trifluoromethanesulfonic acid) (LITFSI) and 2 wt% LiNO3 in 1:1 V/V 1,3-dioxolane (DOL)/1,2-dimethoxy-ethane

(DME). The Li2S6 catholyte solution was chemically synthesized by directly reacting

sulfur with stoichiometric Li2S (molar ration of S: Li2S is 5:1) in a blank electrolyte at

60 ℃ for 24 h to form 1M Li2S6 (molar concentration calculated based on sulfur

atom). The as-prepared CSCNC was punched into round disks with a diameter of 12 mm. The Li2S6 catholyte was added in the above as-synthesized membrane to form a

CSCNC@Li2S6 composite electrode. For comparison, CNC@Li2S6 electrode was also

assembled at the same condition and placed the assembled cells for overnight to wet the cathode thoroughly by the electrolyte. The sulfur mass of 7.11 mg corresponded to 34.5 μL of 1M Li2S6, and the sulfur mass of 14.22 mg was equal to 69 μL of 1M

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S3

Figure S1 (a) Raman spectra and (b) N2 adsorption-desorption analysis of

CNC and CSCNC

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S4

Figure S3 UV-vis spectra and associated color changes of the Li2S6 solution exposure

to CNC and CSCNC

Figure S4 Cycling performance of the CNC@Li2S6 and CSCNC@Li2S6 composite

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S5

Table S1 The comparison of CSCNC with other host cathode materials in Li-S batteries Substances Electrodes with sulfur loading Current rate (C) Initial discharge capacity (mAh g-1₎

Reversible capacity (mAh g-1₎

Cycle number (N) Capacity retention (%)

N-CNFs/S [S1] _1.38-1.54 _0.2 ₁₀₁₀ ₅₉₄ ₁₈₀ _58.8

N-CNFs/S [S2] _2.65-3.53 _0.1 ₉₈₁ ₆₃₆ ₅₀₀ _64.8

NCNFF/S [S3] ₄ _0.5 ₈₃₇ ₇₀₆ ₁₀₀ _84.3

N-rGO/S [S4] _{1.17-1.56 mg} _0.2 ₁₀₄₂ ₉₂₀ ₂₀₀ _88.3

MoS2/CNTs/S [S5] 1.30 mg 0.2 1473 855 50 58.0

CNFs/WS2/S [S6] 1.0-1.2 mg cm-2 1 954 843 500 88.4

MoS2-x/rGO/S [S7] 1.5 mg 0.5 1033 628 600 60.8

ZnS1-x/rGO/S [S8] 2.83 mg 0.2 696 596 100 85.6

Graphene-CoS2/S [S9] 0.53 mg 2 1003 321 2000 32 Graphene-CNT-CoS2/S

[S10]

1.47 mg 0.5 674 581 300 85

CNT/CoS2/S [S11] 0.64 mg 0.2 1232 1035 200 84

Graphene-VS2/S [S12] 5.65 mg 0.2 1015 800 50 78.8 Graphene paper/Li2S8

[S13]

2.42 mg 0.1 1020 612 100 60

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S6

CNF-rGO/Li2S6[S15] 4.23 mg 0.25 961 683 100 71.7 WS2- rGO-CNT/Li2S6

[S16]

0.96 mg 0.1 1227 1113 100 90.7

CNC@Li2S6[This work] 7.11 mg 0.2 1017 647 180 63.6 CSCNC@Li2S6 [This

work]

7.11 mg 0.2 1127 877 200 77.8

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S7

Figure S5 (a) Nyquist plots of EIS spectra of cells with CNC@Li2S6 and

CSCNC@Li2S6 (the insert was equivalent circuit) and (b) the dependence of Zre on

the reciprocal square root of the frequency ω-0.5_{in the low-frequency region for two}

composite electrodes

According to the Equation S1: 𝐷_𝐿𝑖+ = 𝑅2𝑇2

2𝐴2_𝑁4_𝐹2_𝐶2_𝜎2 , the R and T represent the gas

constant (8.314 J mol-1_K-1_{) and the thermodynamics temperature (298.5 K), A}

represents the practical surface area of the electrode (1.13 cm2_{), N represents the}

electron number corresponding to the reaction of the lithium ions (N = 2), F represents the Faraday constant (9.65 × 104_{C mol}-1_{), C represents the molar}

concentration of lithium ions (1.29 mol cm-3_{). The σ represents Warburg diffusion}

coefficient calculated according to the following Equation S2: 𝑍𝑟𝑒 = 𝑅1+ 𝑅2+

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S8

Table S2 Impedance parameters of CNC@Li2S6 and CSCNC@Li2S6 electrodes

Samples Rs (Ω) Rct (Ω) DLi+ (cm2 s-1)

CNC@Li2S6 3.51 16.31 9.07 ×10-9

CSCNC@Li2S6 3.07 12.03 5.63 ×10-8

Calculate section:

The density of sulfur density is 2.07 g cm-3_.

The mass of current collect is 4.37 mg.

The BET specific surface area of current collect is 147.3m2_g-1

The quality of the active substance sulfur is 7.11 mg

The total area of CSCNC: 4.37 mg × 147.3 m2 _g-1_{= 0.64 m}2_{= 6400 cm}2

The total volume of sulfur: 7.11 mg÷2.07 g cm-3_{= 3.43 × 10}-3_cm3

According to the TEM image after the cycle of CSCNC, We can assume that elemental sulfur was evenly coated on the surface of the fiber; therefor the thickness of the cover can be calculated as follows:

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