Synthesis and electrochemical characterizations of Nano-SiO2-coated LiMn2O4 cathode materials for rechargeable lithium batteries

LiMn2O4 spinel cathode materials were coated with 1.0, 2.0 and 3.0 wt.% of SiO2 by polymeric process, followed by 850 °C for 6h in air. The surface coated LiMn2O4 cathode materials were physically characterized using X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy and X-ray photon spectroscopy. XRD patterns of SiO2-coated LiMn2O4 revealed that the coating did not affect the crystal structure, space group Fd3m of the cathode materials, compared to the uncoated LiMn2O4. The surface morphology and particle agglomeration were investigated using Scanning electron microscopy, and the TEM image showed a compact coating layer on the surface of the core materials that had average thickness of about 50 nm. XPS data illustrated that the SiO2 was coated over surface on the LiMn2O4 core materials. The galvanostatic charge and discharge of the uncoated and SiO2-coated LiMn2O4 cathode materials were carried out 0.1 mA/g in the range of 3.0 and 4.5 V at 30 °C and 60 °C. The discharge capacity of 2.0 wt.% of SiO2-coated LiMn2O4 (120 mAh/g) showed only 4.8% loss of the initial capacity (126 mAh/g) over the 100 cycles at 30 °C and (112 mAh/g) showed only 8.9% of loss of the initial capacity (123 mAh/g) over the 100 cycles at 60 °C. The cycleability improvement of the spinel LiMn2O4 coated with 2.0 wt.% of SiO2 is demonstrated at room temperature and elevated temperature. From the analysis of electrochemical impedance spectroscopy (EIS), the improvement of cycleability may be attributed to the suppression on the formation of the passive film and reduction of Mn dissolution, which results from modifying the surface of the spinel LiMn2O4 with SiO2.