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 h ave been investigated. The COPNA precursors were synthesized from an a romatic compound (pyrene, Py) and a cross-linking agent, dimethyl-p-xy lene glycol (DMPXG), with a series of DMPXG/Py molar ratios. The resul ts 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 rati os 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 cu rves of these carbons showed two regions, one of which is the potentia l range of 0 to 1.0 vs. Li/Li+, and the other, the plateau region arou nd 1.0 V. The discharge capacity of the former was almost constant reg ardless of DMPXG/Py, whereas that of the latter increased as DMPXG/Py increased. However, the plateau region disappeared for carbon material s heat-treated above 1000 degrees C. These results suggest that ''cavi ties'' in the carbons heat-treated below 800 degrees C contribute to a ctive charge-discharge of lithium species for a high-capacity carbon a node, 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 agreem ent with the theoretical capacities calculated by using the structural parameters and the butanol displacement densities of the carbon mater ials. This result also supports the validity of our hypothesis, namely , that cavities in the carbon materials contribute to the charges of l ithium species in lithium-ion batteries.