Lithium Insertion in High Capacity Carbonaceous Materials

We report studies of lithium insertion in a variety of organic precursors pyrolyzed below 1000°C. These include two types of petroleum pitch, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polyphenylene sulfide (PPS), and epoxy novolac resin (ENR). Each of these materials shows reversible specific capacities for lithium of between 550 and 900 mAh/g when treated near 700°C. The majority of this high capacity shows large hysteresis; that is the lithium is inserted near 0 V (vs. lithium metal) and removed near 1 V. Furthermore, the amount of capacity showing large hysteresis is well correlated to the hydrogen to carbon atomic ratio of the samples. As the pitch, PVC and PVDF samples are heated above 700°C, the ratio and the specific capacity decrease proportionally, suggesting that the hydrogen in these samples plays an important role. The PPS and ENR samples behave differently; as they are heated above 700°C, the high capacity is maintained as is reduced, although the voltage profile changes dramatically to one without significant hysteresis and with a plateau of several hundred mAh/g near 0 V. We believe that structural differences associated with the presence of single carbon layers in the ENR and PPS samples account for the difference between their behavior and that of the other samples. The materials made from ENR appear to be interesting candidates for high capacity anodes for lithium ion cells.