▎ 摘　　要

A nitrogen-doped carbon layer coating on a 3D graphene framework (NCL@GF) was produced by the in-situ polymerization of a uniform polyimide layer on the graphene framework surface and a carbonization process. The NCL@GF exhibited a 3D macroporous structure with uniform N-doped porous carbon layers and a high 5.4 at. % nitrogen content, which not only effectively enhanced the active sites but also facilitated fast ion and electron transport in the 3D pathways. Consequently, the NCL@GF as the anode of a sodium-ion battery (SIB) exhibited a discharge capacity of 357 mAh g(-1) at 0.1 A g(-1) after 200 cycles, a remarkable rate capability with a capacity of 122 mAh g(-1) at 8 A g(-1), and a super long cycle life with a capacity retention of 70 % capacity after 2500 cycles at 0.5 A g(-1). Such performance is superior to that of previously reported carbon or graphene-based composites.