In situ Raman study of PPP-based disordered carbon as an anode in a Li ion battery

Electrochemical lithium insertion into polyparaphenylene (PPP)-based disordered carbon was investigated using in situ Raman spectroscopy. The peak position of the high frequency Raman band of 1605 cm−1 indicates characteristically at first no change up to 1.0 V and then the peak downshifts from 1605 cm−1 to 1588 cm−1, and finally disappears presumably because of the decrease in optical skin depth giving rise to the conductivity change. For the charging process, the opposite change was observed with some degree of irreversibility in the peak position, reflecting the irreversible discharge/charge capacity of the electrode. The change in peak position is somewhat similar to that observed in well-ordered graphite, which reflects that charge transfer occurs between the Li and the defective carbon layers, even in such a low heat treatment temperature material.