TiO2 coating for long-cycling LiCoO2: A comparison of coating procedures

The cycling properties of LiCoO2 coated with TiO2 by a sol–gel process from an alkoxide precursor and a mechano-thermal process from pre-formed nanoparticles are compared. Electron microscopic images of 1.0 wt.% TiO2-coated particles revealed that the oxide formed a compact coating over the cathode particles. XRD studies showed a general decrease in the value of the lattice parameter c upon coating, indicating that substitutional compounds might have formed on the surface during calcination. R-factor values from XRD studies and galvanostatic charge–discharge studies suggested that a coating level of 1.0 wt.% was optimal for materials with good cycling characteristics. While the sol–gel coating process enhanced cyclability 5-fold, the mechano-thermal process yielded materials that exhibited a 12-fold improvement. The enhanced cyclability is attributed to a suppression of the cycle-limiting hexagonal/monoclinic/hexagonal phase transitions accompanying the charge–discharge processes. Materials with better electrochemical characteristics could be obtained by the mechano-thermally coating process than sol–gel. Furthermore, the mechano-thermal coating process is a simple, inexpensive, environmentally benign and commercially viable one for the production of high-cycling LiCoO2 cathode materials.