Improvement in Cycle Stability of Si Negative Electrode by Cr Doping and by Coating with Carbon Nanotube

Effects of doping Cr and coating carbon nanotube on Si powder were studied as negative electrode of Li ion rechargeable battery. Although the large Li intercalation capacity higher than 1500 mAh/g is exhibited on pure Si, it decreased drastically with the cycle number. Increasing the electrical conductivity by doping chromium is effective for increasing the initial capacity and the cycle stability of Si for Li intercalation, and the reversible capacity of 250 mAh/g was sustained after 5 cycles of charge and discharge. Coating Cr doped Si with the carbon nanotube obtained by decomposition of CH₄4 is effective for increasing the cycle stability, though the initial Li intercalation capacity decreased to ca. 1900 from 2500 mAh/g. Reversible Li intercalation capacity of 750 mAh/g was sustained after 5 cycles of charge and discharge on Si coated with carbon nanotubes.