Functionalized Graphitic Carbon Nitride for Efficient Energy Storage

Using first-principles calculations based on density functional theory, we show that recently synthesized graphitic carbon nitride (g-C 4 N 3 and g-C 3 N 4 ) can be functionalized with Li atoms for use as materials not only for high-capacity hydrogen storage but also for lithium-ion batteries. The unique properties are due to the high density of Li ions firmly adsorbed over nitrogen triangular holes. The gravimetric and volumetric densities of hydrogen in Li 2 C 3 N 4 and Li 2 C 4 N 3 are greater than 10 wt % and 100 g/L, respectively, both exceeding the target set by the U.S. Department of Energy. Similarly, single-layer Li 2 C 3 N 4 is a good candidate for a lithium-ion anode material with a specific capacity almost twice that of graphite, and bulk LiC 4 N 3 can be used as a cathode material with a specific energy twice that of LiCoO 2 . The materials have the added advantage that they are stable against clustering of Li and are nontoxic.