Microstructures and electrochemical properties of Co3O4 anodes coated by silane coupling agents

The surface of a Co3O4 anode for lithium ion batteries (LIBs) was treated by a facile solid-state method using a silane coupling agent. Characterization by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) mapping, and transmission electron microscopy (TEM) indicate that amorphous SiO2 with an average thickness of 5-8 nm was uniformly coated on the surfaces of Co3O4 particles. The SiO2 coating did not induce any change in the crystal lattice and morphology, but reduced the crystallite size of Co3O4 slightly. Electrochemical tests demonstrate that the electrochemical performances of the Co3O4 anode were significantly improved by coating with 2 wt% SiO2. Specifically, when coated with 2 wt% SiO2 using a silane coupling agent, the charge capacity of pure Co3O4 under a constant current density of 50 mA g(-1) was increased to 169.54 and 183.09 mA h g(-1) at room temperature (RT) and 55 degrees C, respectively, and improved by 1.99 and 2.68 times under a high current density of 800 mA g(-1) at RT and 55 degrees C respectively. Furthermore, the charge capacity of coated Co3O4 was 1.35 times higher than that of the untreated material after 50 cycles at 55 degrees C. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests showed that the improved performance is mainly due to the unique coating layer of amorphous SiO2 on the surface, which effectively reduces the direct contact between the anode material and the electrolyte and suppresses the side reactions between Co3O4 and the electrolyte. (C) 2019 Elsevier B.V. All rights reserved.