Electrochemical insertion of lithium into carbon synthesized from condensed aromatics

The electrochemical properties of new carbon materials obtained by the heat-treatment of condensed polynuclear aromatic (COPNA) precursors have been investigated. The COPNA precursors were synthesized from an aromatic compound (pyrene, Py) and a cross-linking agent, dimethyl-p-xylene glycol (DMPXG), with a series of DMPXG/Py molar ratios. The results indicate that the discharge capacities of the carbons heat-treated at 800 degrees C increased as the DMPXG/Py molar ratios increased. The discharge capacities of the carbons derived from them with molar ratios above 1.5 of DMPXG/Py were greater than 372 Ah . kg, corresponding to the composition of stage 1 Li-GIC, LiC6. Moreover, the discharge curves of these carbons showed two regions, one of which is the potential range of 0 to 1.0 vs. Li/Li+, and the other, the plateau region around 1.0 V. The discharge capacity of the former was almost constant regardless of DMPXG/Py, whereas that of the latter increased as DMPXG/Py increased. However, the plateau region disappeared for carbon materials heat-treated above 1000 degrees C. These results suggest that ''cavities'' in the carbons heat-treated below 800 degrees C contribute to active charge-discharge of lithium species for a high-capacity carbon anode, while those in carbon materials heat-treated above 1000 degrees C do not. Furthermore, the observed charge capacities of those carbons heat-treated in the range of 600 td 1600 degrees C showed good agreement with the theoretical capacities calculated by using the structural parameters and the butanol displacement densities of the carbon materials. This result also supports the validity of our hypothesis, namely, that cavities in the carbon materials contribute to the charges of lithium species in lithium-ion batteries.