Synthesis and characterization of lithium–carbon compounds for hydrogen storage

Three carbon materials were prepared for the synthesis of Li–C compounds, such as Li intercalated graphite. The materials were as-received high purity polycrystalline graphite (G), graphite milled under a hydrogen atmosphere (HG), and graphite milled an argon atmosphere (AG). With respect to the difference for them, HG preserved a better crystalline structure than AG. Each material was milled with Li, where the products are denoted as Li-G, Li-HG, and Li-AG. In XRD patterns of Li-G and Li-HG, the peaks corresponding to LiC6 and LiC12 were revealed, while no peaks were observed in the case of Li-AG. However, the formation of lithium carbide Li2C2 was suggested for Li-AG by a thermal analysis under an inert gas. After the hydrogenation, LiH was formed for all the compounds, and graphite was recovered for Li-G and Li-HG. Each hydrogenated compound desorbed H2 with different profile by heating up to 500 °C. As a reaction product, Li2C2 was formed for the hydrogenated Li-HG and Li-AG. In the case of the hydrogenated Li-G with better crystalline structure, Li intercalated graphite were formed after the dehydrogenation. Therefore, it is concluded that the hydrogen absorption and desorption process of Li intercalated graphite was different from those of Li2C2.

Research highlights▶ Li intercalated graphite reversibly absorbs and desorbs H2 below 200 °C. ▶ The H2 ab/desorption reactions proceeds with Li insertion/extraction into graphite. ▶ The H2 storage properties were different from that of Li2C2 reported before. ▶ The reversible hydrogen capacity of Li intercalated graphite was about 1 mass%.