Carbon block anodes with columnar nanopores constructed from amine-functionalized carbon nanosheets for sodium-ion batteries

Earth-abundant sodium is a promising alternative to lithium in rechargeable batteries. However, graphite, the commercial anode material of lithium-ion batteries, cannot be used for sodium-ion batteries (SIBs). Herein, carbon block anodes with columnar nanopores constructed from amine-functionalized carbon nanosheets were synthesized using modified polyacrylonitrile as the carbon source through a simple and economical low-temperature pyrolysis process, delivering high reversible capacity, superior rate capability and remarkable cyclic stability. The surface-dominated redox reaction mechanism in Na storage is the origin of the fast kinetics, since the columnar nanopores which are considered as curled and sealed ultrathin nanosheets, like microjars, not only shorten the ion and electron diffusion length, but also expand the redox sites from the surface to the inner part. This is similar to the storage mechanism in supercapacitors. Moreover, density functional theory computations reveal that the high-level amine groups play an important role in Na storage in the low potential region, endowing the block anode material with both high energy and power density.