Sodium adsorption and intercalation in bilayer graphene from density functional theory calculations

The Na-ion batteries as a low-cost alternative to the Li-ion batteries have attracted considerable attention. The unique properties of bilayer graphene make it attractive for the rechargeable batteries. In the present work, the specific capacity, voltage and migration energy barriers for Na storage in pristine and mono-vacancy defective bilayer graphene are systematically investigated by density functional theory. The calculation results reveal that the mono-vacancy defects improve the specific capacity from 123.97 to 382.54 mAh/g with an appropriate voltage (>0.5 V), which can avoid the formation of clusters and dendrites. Na ions transport quickly from defect-free regions (low energy barriers, 0.15–0.32 eV) to defective regions (large energy barriers, 0.56–0.59 eV) and decelerate by defects. These suggest that defective bilayer graphene is a potential candidate for negative electrode of the Na-ion batteries. Our results provide guidelines to investigate the Na storage in hard carbon and graphene nanosheets.