Anode performance of a Li ion battery based on graphitized and B-doped milled mesophase pitch-based carbon fibers

The structures and anode performance of graphitized and boron-doped milled mesophase pitch-based carbon fibers (mMPCFs) have been comparatively studie d and the results obtained by X-ray diffraction (XRD), SEM, Raman spectrosc opy and electrochemical measurements are discussed. The boron doping at the level of 2.66 at.% (2.4 wt.%) enhances the growth of the crystallite thick ness, L-c(002), of the host mMPCF. The B-doped mMPCFs show a strong Raman p eak near 1365 cm(-1), and a well-defined peak at 1620 cm(-1). The E-2g2 gra phite Raman band at 1580 cm(-1) is shifted to 1590 cm(-1) due to B-doping. On the basis of the integrated intensity ratio R(I-D/I-G), it is suggested that the substitutional boron in the mMPCFs is homogeneously distributed wi thin the graphene layer in the fiber form. Boron doping leads to about an 1 1% increase in charge capacity and also an improved cyclic efficiency. The electrochemical Li intercalation takes place at a higher Voltage in boron-d oped mMPCFs than in undoped mMPCFs by about 40 mV, presumably because the s ubstitutional boron acts as an electron acceptor in the graphite lattice as well as affecting the exposed dislocation edge-type surface. (C) 1999 Else vier Science Ltd. All rights reserved.