Enhancement of the electrochemical Li doping/undoping reaction rate of a graphitic material by an evaporated film of Sn, Zn or Pb

For the purpose of obtaining an improved performance of the carbon anode material for Li-ion secondary batteries a surface modification by metal evaporation onto the carbon surface has been examined. When a film of Pb, Sn or Zn was evaporated onto the surface of a graphitic carbon fiber in vacuo it exhibited markedly higher cyclic voltammogram peaks due to Li doping/undoping as compared to those of an untreated one. This indicates that the electrochemical reactions are enhanced by the treatment. With a simple treatment, Zn gave rise to a good cycleability. However, with a sample covered with a him of Pb or Sn, the enhanced peak current due to the deintercalation of Li was decreased successively upon repetition of the doping/undoping cycling. The gradual deterioration of the Sn deposited carbon could be suppressed by making the deposited Sn film amorphous. (C) 1999 Elsevier Science S.A. All rights reserved.