▎ 摘　　要

A 3D N-doped graphene foam with a 6.8 at% nitrogen content is prepared by annealing a freeze-dried graphene oxide foam in ammonia. It is used as an anode in sodium ion batteries to deliver a high initial reversible capacity of 852.6 mA h g -1 at 1 C between 0.02 and 3 V with a long-term retention of 69.7% after 150 cycles.