Electrochemical intercalation of lithium into disordered carbon heat-treated from poly (p-phenylene) (PPP) at 650 degrees C is investigated. Constant current charge-discharge test, coulometric titration, a.c. impedance and X-ray photoelectron spectrometry (XPS) are performed to provide thermodynamic and kinetic data on the lithium insertion reaction versus x in Li-x(H0.224C)(6) as well as the electronic state of inserted lithium. Our results show that the lithium storage mechanism involves two processes, one is lithium intercalation into the layer structure for 0 < x < 1; the other is lithium being doped onto the surface of micropores for x > 1, or more accurately, onto the surface near the edge sites of microcrystallites, and that the inserted lithium has an ionic state. The above mechanism is basically the same as that proposed for high hydrogen-containing carbons before. The composition dependence of the pre-exponential factor and the activation energy for the self-diffusion of lithium ions suggests that there are significant changes in the mobility of mobile lithium ions and in their concentration. (C) 2000 Elsevier Science Ltd. All rights reserved.