Upconversion luminescence of Er3+/Yb3+-codoped natrium–germanium–bismuth glasses Original Research Article

A mechano-thermal coating method was adopted for obtaining LiCoO2 coated particles with pre-formed pseudo-boehmite nanoparticulate, followed by calcination at 723 K for 10 h. From X-ray diffraction (XRD) analysis it was seen that the coated cathode materials did not show any extraneous phase peaks corresponding to the pseudo-boehmite and the crystal structure, α-NaFeO2, remained the same as pristine LiCoO2. Scanning electron micrograph (SEM) of the coated samples showed that above the 1.0 wt.% coating level, the excess pseudo-boehmite got glued to the coated cathode particles as spherules. TEM images showed that the Al2O3 particles derived from pseudo-boehmite formed ∼20 nm thickness coating layer on the LiCoO2 particles. The XPS/ESCA results revealed that the presence of two different O 1s corresponds to the surface coated Al2O3 and the core material. The electrochemical performance of the coated materials by a cycling study suggest that 1.0 wt.% coated Al2O3 derived from pseudo-boehmite on the two commercial LiCoO2 samples improved cycle stability by a factor of five and 11 times over the pristine LiCoO2 cathode material. Cyclic voltammetry revealed that the hexagonal-monoclinic-hexagonal phase transformations were retained for the coated cathode materials upon continuous cycling.