Carbons derived from poly(p-phenylene) has been found to reversibly store a maximum of 710 mAh of Li per gram of carbon in solid-state Li cells containing polyacrylonitrile-based electrolytes. The amount of reversible capacity was influenced by the current density and by both plasticizer solvent and the Li salt in the electrolyte. An irreversible capacity as high as 465 mAh/g was observed in the first cycle. Thereafter, the cells cycled reversibly, typically delivering 600 mAh of capacity per gram of carbon.