Optimized Structure of Silicon/Carbon/Graphite Composites as an Anode Material for Li-Ion Batteries

Si/carbon/graphite composites were prepared by mixing submicrometer Si, pitch cokes, and graphite powders followed by heat-treatment. Effects of particle sizes and the mixing method on the cycle performance were examined and the optimized composite structure was investigated by transmission electron microscopy and scanning electron microscopy of the composite electrodes. A "surface-coat-type" composite prepared by mixing Si with pitch cokes before mixing with graphite powders showed better cycle performances. The particle size (30 μm) of graphite was also a very important factor in keeping the composite's surface area low, resulting in low irreversible capacity. The downsizing of Si particles was also very effective to have good cycle performances.