Cointercalation of graphite with lithium and organic molecules, such as benzene and tetrahydrofuran (THF), is studied using first-principles calculations. The molecules play an important role in expanding the interlayer graphene distance to $\sim 7.7\text{Å}$. The increased space permits multiple ${\text{H}}_2$ species to be bound to Li cations with a binding energy of 10–22 kJ/mol. Furthermore, in the interstitial area free of Li cations, the negative charge in the graphene sheets enhances the ${\text{H}}_2$ binding energy to $\sim 9\text{kJ}/\text{mol}$ through electrostatic attraction. In order to restrain nucleation of lithium hydrides, the densest Li array is determined to be a ${\text{Li}}_4\left(\text{THF}\right){\text{C}}_{72}$ structure, which absorbs $3.4\text{wt}\%$ hydrogen molecules reversibly. Cointercalation offers an experimentally accessible approach to designing optimized hydrogen storage materials that have not been investigated previously.

• Received 22 July 2008

DOI:https://doi.org/10.1103/PhysRevB.78.144102