Angew. Chem.：A Novel Covalent Assembly Strategy for MoS₂ Nanosheets for Lithium/Sodium-Ion Batteries

Two-dimensional (2D) layered structured materials have received ever-increasing attention due to their unique properties and important applications in the field of energy storage such as lithium/sodium-ion batteries (LIBs/SIBs). However, the interlayers with weak Van der Waals’ interaction are nearly impassable for electrons to transfer across, which leads to slow and incomplete electrode reactions, accompanying by poor rate capability and rapid capacity fading. On the other hand, the layered structure is prone to collapse induced by stress of lithiation and delithiation upon cycling, causing overall performance deterioration of batteries. 

Recently, professors Jinhu Yang and Chi Zhang from Tongji University collaborated with the professor Renchao Che from Fudan University on this issue. They chose MoS₂ nanosheets as a typical layered material, and proposed a novel covalent assembly strategy to construct unique MoS₂/SnS hollow superassemblies (HSs) by using SnS nanodots as covalent linkages between MoS₂ nanosheets. Surprisingly, the MoS₂/SnS HSs as LIB anodes exhibited superior rate performance and long cycling stability, which is among the best comprehensive performance in carbon-free MoS₂-based anodes reported to date. Meanwhile, excellent sodium storage performance was also obtained when the MoS₂/SnS HSs were employed as SIB anodes.

The unique MoS₂/SnS HSs possess a set of advantages for batteries: i) The hollow structure provides abundant active sites and a short diffusion path for Li⁺/Na⁺, favoring a high capacity and excellent rate performance. ii) The integration of MoS₂ and SnS can facilitate the lithium diffusion by reducing the diffusion energy barrier of Li ions based on DFT calculations, which also contribute to the high rate performance. iii) More importantly, the in situ TEM analysis and mechanical simulation indicate that the covalent assembly of MoS₂ nanosheets with SnS nanodots as linkages provides not only mechanically stable framework withstanding lithiation/delithiation, but also direct electron transfer pathways across nanosheets, conducive to stable and fast lithium storage, respectively. The proposed strategy also provides an effective solution to the intrinsic problems of 2D layered materials for energy applications.

This work has been published in the journal of Angew. Chem. Int. Ed., and the postgraduate student Jiajia Ru and Ph.D. student Ting He of Tongji University are the first authors of this work.