HYSTERESIS DURING LITHIUM INSERTION IN HYDROGEN-CONTAINING CARBONS

We studied Lithium insertion in hydrogen-containing carbons heated at temperatures near 700 degrees C. High capacities with large hysteresis (lithium insertion into these carbons at nearly 0 V and removal at ne arly 1 V) were shown to be proportional to the hydrogen content of the samples. It is believed that the lithium atoms may bind on hydrogen-t erminated edges of hexagonal carbon fragments, causing a change in the bond from sp(2) to sp(3). We have carefully studied the electrochemic al insertion of lithium in hydrogen-containing carbons using a variety of charge-discharge rates and cycling. temperatures. These measuremen ts allow the hysteresis to be quantified. A simple model, which treats the bonding change as an activated process, is used to model the hyst eresis in the cells qualitatively.