Electrochemical performance of nano-SiO2 modified LiCoO2 thin films fabricated by electrostatic spray deposition (ESD)

With a mixture of a SiO2 sol and a solution of lithium and cobalt acetates as the precursor, nano-SiO2 modified LiCoO2 films were fabricated by the electrostatic spray deposition (ESD) technique. The SiO2 content of these films was 0, 5, 10, 15 and 20 wt%, respectively. Their structure and electrochemical properties were characterized by means of X-ray diffraction, scanning electron microscopy, galvanostatic cell cycling, AC impedance spectroscopy and cyclic voltammetry. Li2CoSiO4 was found formed in the SiO2-containing films. The film with 15 wt% SiO2 shows the best cycling stability with the capacity of 130 mAh/g in the voltage range between 2.7 and 4.3 V at the current density of 0.1 mA/cm2. Due to its resulted small cell impedance, it has excellent rate capability. A LiCoO2 (shell)/SiO2 (core) structure model is proposed to explain the improved properties of these films.