Ultrafast Sodium Storage through Capacitive Behaviors in Carbon Nanosheets with Enhanced Ion Transport

Sodium-ion batteries are regarded as a promising alternative for scalable electricity storage, but the rate capability is still a scientific challenge to be solved, owing to the poor Na+ kinetics in electrodes. Herein, nitrogen-doped carbon nanosheets with rich defects, nanopores and various interlayer spacings are prepared by pre-carbonized polymer sheets at different temperatures followed by sodium amide treatment. Combination of thin nanosheets, nanopores and large interlayer spacing can boost the rapid Na+ diffusion, as proven by the calculation of the diffusion coefficient. Meanwhile, the kinetics analysis demonstrates the capacitive behaviors, which favor fast Na+ storage. When applied as an anode, the material exhibits superior rate capability (111.1 mA h g(-1) even at 20 A g(-1)), remarkable cycle stability (over 2000 cycles) and ultrahigh initial coulombic efficiency (81.4 %). Furthermore, this work demonstrates a new way to develop attractive high-rate carbon anode materials for sodium-ion batteries.