Electrochemical performance of nano-SiO₂ modified LiCoO ₂ 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 LiCoO ₂ 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.