SnO₂-coated LiCoO₂ cathode material for high-voltage applications in lithium-ion batteries

In order to improve the electrochemical performances of LiCoO₂ cathode in high voltage cycling range (3.0-4.5 V), SnO₂ thin film has been deposited on the surface of electrode material by an electron cyclotron resonance-metal organic chemical vapor deposition (ECR-MOCVD). Scanning electron microscopy (SEM) images and X-ray diffraction (XRD) patterns confirm the presence of SnO₂ thin layers on the tape-casted electrode composed of nanocrystalline structure with agglomerated grain size ranging from 30 to 40 nm. The electrochemical tests show that the SnO₂ coating layer significantly enhances the cycling performance of LiCoO₂ cathode material. While the bare LiCoO₂ cell does not work after 370 cycles, the surface-modified electrode exhibits the extended performance over 500 cycles with excellent capacity retention. In addition, it is also observed that SnO₂ coating material is able to amplify the initial discharge capacity of bare LiCoO₂ from 172 to183 mAhg^{- 1} at 1 C and effectively increase the coulombic efficiency of pristine LiCoO₂ cathode. We conclude that these electrochemical improvements are strongly due to the suppression of charge transfer resistance and prevention of side reactions during the charge/discharge process via surface coating of electrodes.