$B_2O_3$-doped carboneous powders for the anode material in lithium ion secondary batteries were prepared with various graphitization atmosphere. It was studied that such the cell performances as capacity and efficiency are related to the surface micro-structures of the graphitized carboneous powders using a transmission electron microscopy.
Amorphous carbon is unsuitable to be prepared as the cell electrodes. The doping of $B_2O_3$ into carbon leads to form the boron-based compounds such as $B_4C$ and BN. These play roles in the catalysis on the growth of graphitic crystals and increases the capacity.
It was analyzed that highly-crystallized graphites distributed on the surface of particles when the soft carbon (cokes) doped with $B_2O_3$ is graphitized with high-resolution transmission electron microscopy (HRTEM) images and electron diffraction patterns. When the soft carbon doped with $B_2O_3$ was graphitized in $N_2$ atmosphere(air), hexagonal boron nitrides was formed at the edge of graphite layers, which was analyzed to be the cause of decrease in the cell capacity and efficiency. And such special structures as the edge of graphite layers, loop structures and onion rings were likely to influences on the cell efficiency.
$B_2O_3$/carboneous powders were coated with mesophase pitch (MP), amorphous carbon and graphitized. Coated layers were graphitized in parts, but coated amorphous layers caused the decrease of the cell efficiency.
In the selected area electron diffraction (SAED) patterns, we observed the double diffraction by the strongly diffracted electron beam and the elliptical diffraction patterns. Through these selected area electron diffraction patterns, the structure of graphites and the degrees of graphitization were analyzed.
