Application of Separators Modified by Carbon Nanospheres Enriched with α-MoC1-x Nanocrystalline in Lithium Sulfur Batteries

doi:10.15541/jim20190237

Abstract

Abstract:

Carbon nanospheres enriched with α-MoC_1-_x nanocrystalline (α-MoC_1-_x/CNS) were synthesized by self-assembly and applied as a mediator for the surface of commercial polypropylene (PP) separator. Compared with pristin PP separator, the cycling stability and rate performance of the lithium-sulfur batteries with the modified α-MoC_1-_x/CNS-PP separator are significantly improved and the battery with α-MoC_1-_x/CNS-PP separator exhibits an initial discharge capacity of 1129.7 mAh/g at 0.5C and retains 855.5 mAh/g after 100 cycles with above 98% Coulombic efficiency. Remarkably, the capacity loss rate is only 7.7% after 48 h static storage. Combined with the morphology and XPS analysis of α-MoC_1-_x/CNS, it is found that the designed α-MoC_1-_x/CNS-PP separator prevents the migration of lithium polysulfide to the anode during the process of charge and discharge in lithium sulfur batteries. Formations of Mo-S bonds, thiosulfate and polythionate are attributed to the contact between lithium polysulfide and α-MoC_1-_x/CNS, which further restrains active material in cathode region and improves the performance of lithium- sulfur batteries consequently.

Key words: lithium sulfur battery, shuttle effect, molybdenum carbide, sulfur cathode

CLC Number:

O646

WANG Jianing, JIN Jun, WEN Zhaoyin. Application of Separators Modified by Carbon Nanospheres Enriched with α-MoC_1-_x Nanocrystalline in Lithium Sulfur Batteries[J]. Journal of Inorganic Materials, 2020, 35(5): 532-540.

Figures/Tables 8

Fig. 1 SEM images of (a, d) the precursor of the α-MoC1-x/CNS composite and (b-c, e) the α-MoC1-x/CNS composite; (f) Mo, C and O element mappings and (g-i) TEM images of the α-MoC1-x/CNS composite

Fig. 2 (a) XRD patterns of the α-MoC1-x/CNS composite and its precursor; (b) Mo 3d and (c) O 1s XPS spectra, (d) N2 adsorption-desorption isotherm (inset: pore size distribution), (e) Raman spectrum, (f) TGA curve (under air flow) of the α-MoC1-x/CNS composite

Fig. 3 (a) Photograph of the synthesized α-MoC1-x/CNS-PP separator with positive and negative sides; (b) SEM image and (c) measurement of the electrolyte contact angle for Celgard 2400 separator; (d) Typical cross-sectional, (e) surface SEM images and (f) measurement of the electrolyte contact angle for α-MoC1-x/CNS-PP separator; (g-i) Corresponding elemental mappings of C, O, Mo in (e)

Fig. 4 Cyclic voltammograms of the Li-S battery with (a) Celgard 2400 separator and (b) α-MoC1-x/CNS-PP separator; (c) Rate performances with different separators at various current densities; (d) Charge-discharge voltage profiles at various current densities of the Li-S battery with α-MoC1-x/CNS-PP separator

Fig. 5 Electrochemical impedance plots of Li-S battery with α-MoC1-x/CNS-PP separator (a) before and (b) after 30 cycles

Fig. 6 Cycling performance of the Li-S battery with (a, c) Celgard 2400 separator and (b, d) α-MoC1-x/CNS-PP separator at (a-b) 0.5C and (c-d) 1C

Fig. 7 Self-discharge tests for lithium sulfur batteries with Celgard 2400 separator or α-MoC1-x/CNS-PP separator (a) Discharge-charge profiles within 120 h; (b) Corresponding cycling performance

Fig. 8 (a) XPS survey spectra of α-MoC1-x/CNS and α-MoC1-x/CNS-Li2S6; (b) Mo3d and (c) S2p XPS core level spectra of α-MoC1-x/CNS-Li2S6

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