Impact of hydrogen on lithium storage on graphene edges

Abstract

Hard carbons are extensively studied as high-capacity lithium storage materials. These excess capacities are closely related to the lithium adsorption on the active sites of the carbons. As a common residual element of the hard carbons, the presence of the hydrogen (H) strongly affects the lithium storage and its capacity. Herein, models of graphene nanoribbons with bare zigzag edges (GC) and with pyridinic nitrogen edges (GN) are constructed, respectively, to study the influence of hydrogen by the density functional theory (DFT) calculations. Our calculations show that there is a strong interaction between Li and the H-free GC or GN. However, the presence of H on the edges lowers the average potential, and the interaction becomes significantly weak. The Li atoms can replace the H atoms and form LiN bonds on the H-terminated GN edges, but this hardly takes place on the H-terminated GC. This study fills in the gaps about the H influence on the lithium adsorption in the carbonaceous materials and helps to optimize the structure of the carbon for lithium adsorption.