α-MoC1-x纳米晶富集碳球修饰隔膜对锂硫电池性能的影响

doi:10.15541/jim20190237

摘要/Abstract

摘要：

采用自组装及热处理方法合成α-MoC_1-_x纳米晶富集的纳米碳球(α-MoC_1-_x/CNS), 并将其涂覆在商用聚丙烯隔膜上, 对隔膜实现了界面修饰。电化学性能显示, 与普通的聚丙烯隔膜相比, 采用修饰的α-MoC_1-_x/CNS-PP隔膜组装的锂硫电池的循环稳定性和倍率性能均得到明显提升, 在0.5C条件下, 电池首周放电比容量提升至1129.7 mAh/g, 经过100周充放电循环后, 电池仍具有855.5 mAh/g的放电比容量, 且在此循环过程中, 库伦效率始终大于98%。在自放电测试中, 电池经过48 h静置后的容量损失率仅为7.7%。结合α-MoC_1-_x/CNS的微观形貌及XPS分析可知, 在锂硫电池充放电过程中, α-MoC_1-_x/CNS修饰层有效地阻挡了多硫化锂向负极侧的扩散迁移, 且当α-MoC_1-_x与多硫离子接触时能产生Mo-S键、硫代和连多硫酸根产物, 进一步巩固了活性物质被约束的程度, 从而使电池性能得到提升。

关键词: 锂硫电池, 穿梭效应, 碳化钼, 硫正极

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

中图分类号:

O646

王佳宁, 靳俊, 温兆银. α-MoC_1-_x纳米晶富集碳球修饰隔膜对锂硫电池性能的影响[J]. 无机材料学报, 2020, 35(5): 532-540.

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.

图/表 8

图1 (a, d)α-MoC1-x/CNS前驱体和(b~c, e)α-MoC1-x/CNS的SEM照片; (f)α-MoC1-x/CNS的Mo、C、O元素分布图和(g~i)TEM照片

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

图2 (a)α-MoC1-x/CNS及其前驱体的XRD图谱; α-MoC1-x/CNS的(b)Mo 3d和(c)O 1s XPS图谱, (d)氮气吸附-脱附等温曲线(插图为孔径分布图), (e)Raman光谱和(f)在空气中的热重分析图

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

图3 (a)α-MoC1-x/CNS-PP的表面及背面两侧的照片; Celgard 2400的(b)表面SEM照片, (c)电解液接触角测试; α-MoC1-x/CNS-PP的(d)截面和(e)表面SEM照片(插图为α-MoC1-x/CNS-PP折叠后的照片), (f)电解液接触角测试; (g~i)图(e)所对应的C、O、Mo元素分布图

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)

图4 采用(a)Celgard 2400和(b)α-MoC1-x/CNS-PP的锂硫电池的循环伏安曲线, (c)普通Celgard 2400和α-MoC1-x/CNS-PP的锂硫电池倍率性能, (d)不同电流密度下α-MoC1-x/CNS-PP的锂硫电池的充放电曲线

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

图5 采用α-MoC1-x/CNS-PP的锂硫电池在(a)循环前和(b)循环30周后的阻抗图谱

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

图6 采用(a, c)Celgard 2400和(b, d)α-MoC1-x/CNS-PP的锂硫电池在(a~b)0.5C和(c~d)1C电流密度下的循环性能

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

图7 采用Celgard 2400和α-MoC1-x/CNS-PP的电池的自放电测试

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

图8 (a)α-MoC1-x/CNS与α-MoC1-x/CNS-Li2S6的XPS图谱; α-MoC1-x/CNS-Li2S6的(b)Mo3d和(c)S2p XPS图谱

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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