Superstructure MOF as a framework to composite MoS2 with rGO for Li/Na-ion battery storage with high-performance and stability

Abstract

Metal sulfides, one kind of electrode material with very high theoretical capacity, have been widely studied for use in lithium and sodium ion batteries. However, there are some problems hindering their applications in electrodes, such as low conductivity and volume expansion. The MOF introduces metals with different coordination strengths into an existing MOF structure, which improves the performance of the electrode to a certain extent. In this paper, Fe/Zn bimetallic MOF rod-like superstructure was prepared based on Ostwald theory. Accompanied by sulfuration, the MOF was effectively combined with MoS₂ and GO, and the objective materials Fe₇S₈-C/ZnS-C@MoS₂/rGO composites were successfully prepared. The MOF material provides a good frame and an efficient electron transport path, while the robust rGO wall effectively inhibits the pulverization of materials during the lithium/sodium intercalation/escalation courses. This particular material exhibited excellent cycling and rate capability performance when used in Li/Na-ion batteries. When used in Li-batteries, the electrode material delivered a specific capacity of 1598.3 mA h g⁻¹ at 0.1 A g⁻¹ and remained at 1196.7 mA h g⁻¹ even after about 100 cycles and further exhibited a specific capacity of 368.68 mA h g⁻¹ at the current rate of 5 A g⁻¹ even after 1000 cycles, respectively. As for sodium batteries, these electrode materials exhibited an initial reversible capacity of 1053.6 mA h g⁻¹ at 0.1 A g⁻¹ and the reversible capacity was still as high as 592.2 mA h g⁻¹ after 200 cycles. It is perhaps that this composite material with its particular architecture and composition is greatly beneficial for electron transfer and Li/Na ion diffusion. In the repeated physicochemical/nutrifying process, the appropriate distance between adjacent MOFs is of great help in preventing volume changes and thus improving the electrochemical performance.