Nitrogen doped three-dimensional graphene (N-3DG) with improved catalytic activities and optimized pore structure is prepared through facile hydrothermal and subsequent annealing processes. When employed as a novel free-standing cathode for Li-O-2 batteries, its special three-dimensional structure with increased active sites, large pore volume and numerous available macropores and mesopores effectively facilitates the discharge products deposition, oxygen diffusion and electrolyte infiltration. Compared with pristine three-dimensional graphene (3DG), N-3DG delivers a higher specific capacity of 7300 mAh g(-1) at the current density of 50 mA g(-1) and better cycling stability. (C) 2016 Elsevier Ltd. All rights reserved.