Study on MXene-Carbon Black/Sulfur Composite in Integrated Electrode of Lithium-Sulfur Batteries

Ye-Peng Fan, 1. Collaborative Innovation Center of Sustainable Energy Materials, Guangxi University, Nanning 530004, Guangxi, China;2. School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, Guangxi, China;
Ye-Qiang Luo, 1. Collaborative Innovation Center of Sustainable Energy Materials, Guangxi University, Nanning 530004, Guangxi, China;2. School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, Guangxi, China;
Pei-Kang Shen, 1. Collaborative Innovation Center of Sustainable Energy Materials, Guangxi University, Nanning 530004, Guangxi, China;Follow

Corresponding Author

Pei-Kang Shen(pkshen@gxu.edu.cn)

Abstract

Lithium-sulfur (Li-S) batteries are considered as a promising energy storage device due to their ultrahigh theoretical energy density of 2500 Wh·kg^-1 and low cost. However, the practical application of Li-S batteries is seriously limited by their low actual energy density, the shuttle effect of polysulfides (LiPSs), and the insulating nature of sulfur and lithium sulfides. Carbon materials have been developed in the design of sulfur hosts due to their adjustable pore structure and high electrical conductivity, but their non-polar surfaces have weak interactions with LiPSs. Herein, MXene-carbon black/sulfur (Ti₃C₂T_x-CB/S) composites were prepared and applied to the integrated electrodes of Li-S batteries. The CB/S was prepared via a melting-diffusion method and Ti₃C₂T_x MXene nanosheets were synthesized by etching Ti₃AlC₂ MAX with LiF/HCl. After mixing CB/S and Ti₃C₂T_x, Ti₃C₂T_x-CB/S cathode material was obtained and coated on commercial separator (PP) to prepare Ti₃C₂T_x-CB/S-PP integrated electrodes. On the one hand, the two-dimensional Ti₃C₂T_x nanosheets dispersed in the CB/S particles not only serve as multiple physical barriers to inhibit the diffusion of LiPSs, but also have strong chemical interactions with them, effectively alleviating the shuttle effect. Thus, Ti₃C₂T_x improves the conductivity of CB/S composite, which is beneficial to the reaction kinetics of the cathode. Furthermore, the design of Ti₃C₂T_x-CB/S-PP integrated electrode increases the energy density of Li-S batteries. X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to analyze the structures, morphologies, and surface chemical composition of the synthesized materials. The results of constant current charge/discharge tests showed that Ti₃C₂T_x-CB/S-PP electrode achieved superior rate performance and cycling performance than CB/S-PP electrode. The initial discharge capacity of Ti₃C₂T_x-CB/S-PP electrode at 0.1 C current was 1028.8 mAh·g^-1, higher than 896.8 mAh·g^-1 of CB/S-PP electrode. The cycling test at 0.2 C indicated that Ti₃C₂T_x-CB/S-PP maintained a discharge capacity of 726.4 mAh·g^-1 after 80 cycles, better than CB/S-PP (529.2 mAh·g^-1). Moreover, due to the improved utilization of the active material at the interface between the cathode and the separator, Ti₃C₂T_x-CB/S-PP electrode also showed better cycling stability compared to the Ti₃C₂T_x-CB/S-Al electrode based on the traditional aluminum foil current collector. The capacity degradation rate of Ti₃C₂T_x-CB/S-PP was only 0.072% per cycle in a long-term cycling test of 400 cycles at 0.5 C, while that of Ti₃C₂T_x-CB/S-Al was 0.10%. The strategy of using Ti₃C₂T_x-CB/S to construct an integrated electrode provides a new direction for Li-S batteries with high performance and high energy density.

Graphical Abstract

Keywords

lithium-sulfur batteries, integrated electrode, shuttle effect, Ti3C2Tx MXene

DOI Link

https://doi.org/10.13208/j.electrochem.201231

Publication Date

2021-08-28

Online Available Date

2021-01-25

Revised Date

2021-01-13

Received Date

2020-12-30

Recommended Citation

Ye-Peng Fan, Ye-Qiang Luo, Pei-Kang Shen. Study on MXene-Carbon Black/Sulfur Composite in Integrated Electrode of Lithium-Sulfur Batteries[J]. Journal of Electrochemistry, 2021 , 27(4): 377-387.
DOI: Lithium-sulfur (Li-S) batteries are considered as a promising energy storage device due to their ultrahigh theoretical energy density of 2500 Wh·kg^-1 and low cost. However, the practical application of Li-S batteries is seriously limited by their low actual energy density, the shuttle effect of polysulfides (LiPSs), and the insulating nature of sulfur and lithium sulfides. Carbon materials have been developed in the design of sulfur hosts due to their adjustable pore structure and high electrical conductivity, but their non-polar surfaces have weak interactions with LiPSs. Herein, MXene-carbon black/sulfur (Ti₃C₂T_x-CB/S) composites were prepared and applied to the integrated electrodes of Li-S batteries. The CB/S was prepared via a melting-diffusion method and Ti₃C₂T_x MXene nanosheets were synthesized by etching Ti₃AlC₂ MAX with LiF/HCl. After mixing CB/S and Ti₃C₂T_x, Ti₃C₂T_x-CB/S cathode material was obtained and coated on commercial separator (PP) to prepare Ti₃C₂T_x-CB/S-PP integrated electrodes. On the one hand, the two-dimensional Ti₃C₂T_x nanosheets dispersed in the CB/S particles not only serve as multiple physical barriers to inhibit the diffusion of LiPSs, but also have strong chemical interactions with them, effectively alleviating the shuttle effect. Thus, Ti₃C₂T_x improves the conductivity of CB/S composite, which is beneficial to the reaction kinetics of the cathode. Furthermore, the design of Ti₃C₂T_x-CB/S-PP integrated electrode increases the energy density of Li-S batteries. X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to analyze the structures, morphologies, and surface chemical composition of the synthesized materials. The results of constant current charge/discharge tests showed that Ti₃C₂T_x-CB/S-PP electrode achieved superior rate performance and cycling performance than CB/S-PP electrode. The initial discharge capacity of Ti₃C₂T_x-CB/S-PP electrode at 0.1 C current was 1028.8 mAh·g^-1, higher than 896.8 mAh·g^-1 of CB/S-PP electrode. The cycling test at 0.2 C indicated that Ti₃C₂T_x-CB/S-PP maintained a discharge capacity of 726.4 mAh·g^-1 after 80 cycles, better than CB/S-PP (529.2 mAh·g^-1). Moreover, due to the improved utilization of the active material at the interface between the cathode and the separator, Ti₃C₂T_x-CB/S-PP electrode also showed better cycling stability compared to the Ti₃C₂T_x-CB/S-Al electrode based on the traditional aluminum foil current collector. The capacity degradation rate of Ti₃C₂T_x-CB/S-PP was only 0.072% per cycle in a long-term cycling test of 400 cycles at 0.5 C, while that of Ti₃C₂T_x-CB/S-Al was 0.10%. The strategy of using Ti₃C₂T_x-CB/S to construct an integrated electrode provides a new direction for Li-S batteries with high performance and high energy density.