Characterization of polyparaphenylene (PPP)-based carbons

Polyparaphenylene (PPP)-based carbons heat-treated at temperatures (T-HT) from 600 degrees C up to 3000 degrees C have been characterized both structurally and in terms of their physical properties. Special attention is given to PPP heat-treated at 700 degrees C (denoted by PPP-700), since samples heat-treated to this temperature were observed to have exceptionally high lithium affinities when electrochemically doped with Li. At low T-HT below 700 degrees C, it is found that the local structure of PPP-based samples can be characterized mostly in terms of a disordered polymer. As a result of heat treatment to high temperature, PPP-based carbon shows graphitization behavior with regard to x-ray diffraction d(002) (graphite c-axis d-spacing) development and to the increase of the Raman I-G/I-D intensity ratio (where I-G and I-D are the integrated intensities of the 1580 cm(-1) and 1360 cm(-1) Raman modes, respectively), as is found in so-called graphitizing carbons. However, development of the c-axis crystallite size (L(c)) is restricted to very small values, in the range of so-called nongraphitizing carbons, while the a-axis crystallite Size (L(a)) attains values up to roughly 120 Angstrom for heat treatments near 3000 degrees C. These structural properties of PPP-based carbons are consistent with the observed electrical characteristics and their dependence on T-HT. LOW temperature magnetic susceptibility measurements were analyzed, along with Raman spectra, allowing for the characterization of disorder in terms of localized spin states for several heat-treated PPP samples. By interpreting the results of these various characterization techniques, we are able to present an insightful perspective on the nature of PPP-based carbons and the role of PPP-700 as an effective lithium host material for secondary battery applications.