▎ 摘　　要

The formation of Na-x C-72 (1 = 5. The maximum sodium storage capacity is 124 mAh/g, corresponding to a structure of Na-4 C-72. The weak ionic bonds between Na atoms and graphene are formed by charge transfer from Na 3s to graphene pi*, and metallic bonds are found between Na atoms in Na cluster as revealed by density difference, ELF and Mulliken population. Moreover, PDOS results show that the Fermi level of Na-x C-72 (1