Preformed boehmite nanoparticles as coating materials for long-cycling LiCoO₂

A simple mechano-thermal coating procedure for the production of long-cycling LiCoO₂ is described. Preformed nanoparticulate boehmite was used as the coating material. The coating procedure resulted in the cathode particles covered in a 20- 30 nm thick kernel of boehmite, as revealed by TEM examination. XRD studies showed that the lattice parameter c diminished upon coating, indicating that a substitutional compound of the composition Li _xAl_yCo_1-y,O₂ may have formed upon calcination. SEM images, R-factor values from XRD studies and galvanostatic charge-discharge studies showed that a coating level of 1.0 wt % gave an optimal performance in capacity and cyclability. SEM images showed that above the 1.0 wt % coating level, the excess boehmite adhered to the coated cathode particles as sperules. ESCA depth profile analysis showed partial diffusion of aluminum from the surface to the interior. Galvanostatic cycling studies showed that at a coating level of 1.0 wt %, cyclability improved three- and twelve-fold for the two commercial LiCoO₂ samples tested. Cyclic voltammetry revealed that the hexagonal- monoclinic-hexagonal phase transformations during cycling were suppressed in the coated cathode materials.