Suffering from the sluggish kinetics resulting from the inferior conductivity of manganese dioxide (MnO 2 ), many endeavors have been devoted to promoting the electrochemical performance of MnO 2 . Doping heteroatoms into host materials has emerged as an effective strategy to generate lattice vacancies for fast diffusion of ions/electrons in MnO 2 -based materials for supercapacitors (SCs). To eliminate the use of dangerous solvents and the severe reaction conditions used in previous reports, in this work, we first obtain N-doped MnO 2 (N−MnO 2 ) nanosheets with abundant oxygen vacancies simultaneously by a mild hydrothermal reaction. Thus, thanks to the mutual effect of N doping and oxygen vacancies, the capability of ion diffusion for N−MnO 2 /NGCF (NGCF represents N-doped single-wall carbon nanotube cross-linked graphene composite film) has increased an order of magnitude (1.68 × 10 −11 cm 2 s −1 compared with 8.42 × 10 −13 cm 2 s −1 for MnO 2 /NGCF) and shows superior rate capability, where at 30 A g −1 a capacitance retention of 51.7% remains, i.e., 185.1 F g −1 , compared with 44% at 15 A g −1 for MnO 2 /NGCF. In addition, we apply ex situ X-ray diffraction (XRD) and scanning electron microscopy (SEM) to verify the fact that nitrogen doping with abundant vacancies will benefit reversible intercalation/stripping of Na + by triggering the phase change from MnO 2 to MnOOH for N−MnO 2 compared with MnO 2 with adsorption/desorption during the charge−discharge process, which has never been discussed before. Excitingly, an asymmetric supercapacitor (ASC), fabricated by N−MnO 2 /NGCF as a cathode and MnO 2 /NGCF as an anode, delivers a maximum energy and power density of 75.3 Wh kg −1 and 18.1 × 10 3 W kg −1 , respectively. This work provides an approach to design self-standing advanced N-doped MnO 2 and a deeper insight into the mode of reaction of MnO 2 in neutral electrolyte for aqueous SCs.