Lithium-Sulfur Batteries with a 1T MoS2/Graphene As a Highly Efficient Electrocatalyst

Advanced energy-storage technologies are urgently needed to satisfy the energy demands of the society. Lithium-sulfur (Li-S) batteries are one of the most attractive candidates for next-generation energy-storage technology.1-3 However, it is extremely crucial to suppress the inherent "polysulfide shuttle" for the Li-S batteries to be viable.4, 5 Although electrocatalysis has been shown to enhance cell stability, further performance improvement of Li-S cells is seriously hindered due to a lack of understanding of the electrocatalysis mechanism on the sulfur redox process. Herein the electrocatalysis mechanism on the sulfur redox process is revealed based on both experimental and theoretical work.6 We present the synthesis of well-designed, freestanding, three-dimensional graphene/1T MoS2 (3DG/TM) heterostructures as a highly efficient electrocatalyst for lithium polysulfide (LiPS) conversion.7 The metallic 1T MoS2 nanosheets are hydrophilic with rich active sites and high electronic conductivity that is six orders of magnitude higher than that of 2H MoS2. The high electronic conductivity facilitates fast electron transfer, the hydrophilic property benefits ion diffusion, and the dense active sites ensure sufficient catalytic activity for LiPSs. The 3DG/TM heterostructures of our designed material can maximize the aspect ratio of active catalytic sites. The freestanding, porous morphology of the 3DG/TM material facilitates electrolyte accessibility, enabling better ion transport. Benefitting from these synergistic effects (Fig. 1a), the cells with 3DG/TM exhibit excellent specific capacity and outstanding cycling stability. Furthermore, the fundamental understanding for the enhanced catalytic activity in the MoS2-supported systems is revealed via experimental characterizations and theoretical calculation, which provide new insights and opportunities to develop advanced Li-S batteries with highly efficient electrocatalysts for LiPSs. Based on the deep understanding of the electrocatalysis of LiPSs conversion, the well-designed 3DG/TM heterostructures with rich electrocatalytically active sites ensure high catalytic activity and thus significantly improve the electrochemical performance of Li-S batteries. Even with a very high sulfur loading (10 mg cm-2), the S/3DG/TM cathode not only effectively mitigates the LiPS shuttling, but also delivers excellent specific capacity, outstanding rate capability, and pronounced cycling stability for an impressive number of 500 cycles (Fig. 1b). Fig. 1 (a) The conversion process of LiPSs on a graphene surface with 1T MoS2. The 3DG/TM heterostructures work as a highly efficient electrocatalyst for LiPSs conversion. (b) Long-term cycling cyclability of 3DG/TM with catholyte at 1C rate. REFERENCES1 Y. Fu, C. Zu, A. Manthiram, J. Am. Chem. Soc. 2013, 135, 18044. 2 J. He, Y. Chen, A. Manthiram, Energ. Environ. Sci. 2018, 11, 2560. 3 J. He, Y. Chen, A. Manthiram, iScience 2018, 36. 4 G. Tan, R. Xu, Z. Xing, Y. Yuan, J. Lu, J. Wen, C. Liu, L. Ma, C. Zhan, Q. Liu, T. Wu, Z. Jian, R. Shahbazian-Yassar, Y. Ren, D. J. Miller, L. A. Curtiss, X. Ji, K. Amine, Nature Energy 2017, 2, 17090. 5 J. He, Y. Chen, W. Lv, K. Wen, C. Xu, W. Zhang, Y. Li, W. Qin, W. He, ACS Nano 2016, 10, 10981. 6 G. Babu, N. Masurkar, H. Al Salem, L. M. R. Arava, J. Am. Chem. Soc. 2016, 139, 171. 7 J. He, G. Hartmann, M. Lee, G. S. Hwang, Y. Chen, A. Manthiram, Energ. Environ. Sci. 2019 (10.1039/C8EE03252A). Figure 1