Large vacancy-defective graphene for enhanced lithium storage

For lithium-ion batteries (LIBs), the dilemma of low-capacity commercial graphite electrode has forced researchers to keep developing high-capacity electrodes. While two-dimensional (2-D) carbon materials are widely used in the field of energy storage due to their excellent physical and chemical properties. Here, based on density functional theory, we systematically investigate Li adsorption and diffusion on graphene with vacancy defects of different sizes, namely GVn (n = 2, 4, 6, 10, and 13). Our results show that, unlike pristine graphene, these defective structures can adsorb Li atoms stably and dispersedly. The adsorption energy of Li gradually enhances as it approaches the vacancy defects. Furthermore, the diffusion of Li on the surfaces of the GVn (n = 6, 10, and 13) is more difficult due to the presence of large vacancy defects. Fortunately, when their vacancy defects are filled with Li atoms, the corresponding diffusion barriers would decrease dramatically. What is most interesting is that as the size of vacancy defect increases, its corresponding Li storage capacity also increases considerably. The calculated storage capacities of GV10 and GV13 are 614 mA h g−1 and 637 mA h g−1, respectively, which exceed that of conventional graphite electrode and many other 2-D graphene-like electrodes. Thus, we believed that is an interesting and competitive example for developing high-capacity electrodes.