Regulable Electron Transfer on ZnS/CoS₂/CC Prepared by an MOF-on-MOF Strategy for Robust LIB Performance

Abstract

The anode electrochemical performance of lithium-ion batteries (LIBs) depends mainly on the structural stability of the electrode material and its conductivity, and its energy storage mechanism is mainly derived from the Faraday charge transfer that occurs around the electrode surface and the Faraday pseudocapacitance. Due to the high theoretical specific capacity of transition metal sulfides (TMS) and the mechanical stability and high conductivity of carbon cloth (CC), the strategy of growing TMS in situ in CC can simultaneously improve reversibility, structural stability, and conductivity. In this work, hierarchical 3D-Zn-ZIF-on-2D-Co-ZIF precursors are grown in situ on CC by a strategy called MOF-on-MOF, and the ZnS/CoS2/CC stable framework is obtained by sulfuration. The interfacial electron transfer mechanism was explored by ultraviolet photoelectron spectroscopy, and the synergistic interaction between ZnS and CoS2 in ZnS/CoS2/CC was further elaborated. Specifically, the work functions of ZnS and CoS2 are 15.9 and 16.6 eV, respectively, and the corresponding Fermi energy levels are 5.32 eV for ZnS and 4.62 eV for CoS2. Therefore, after doping with ZnS, electrons will be transferred and enriched from the ZnS surface to the CoS2 surface to accelerate the reduction process of CoS2, and this plays such a decisive part during the electrochemical reaction. Thereby, the charge enrichment and rapid transfer at the ZnS/CoS2/CC interface facilitates the Faraday reaction. As a result, ZnS/CoS2/CC exhibits an outstanding electrochemical performance as an anode material for LIBs, with a capacity of up to 1644.7 mA h g–1 after 160 cycles at a high current density of 1 A g–1.