N-doped reduced graphene oxide/Co0.85Se microflowers with high mass loading as battery-type materials for quasi-solid-state hybrid supercapacitors

• N-rGO/CS microflowers with high mass loading were prepared. • The introduction of N-rGO could increase the specific surface area and enhance conductivity. • N-rGO/CS//AC quasi-solid-state HSCs were fabricated. • A high energy density of 4.65 mWh cm −3 were achieved for the assembled HSCs. In this work, we prepared N-doped reduced graphene oxide/Co 0.85 Se (N-rGO/CS) microflowers through a two-step method. Since introducing N-doped rGO, the fabricated N-rGO/CS electrode with a high mass loading (~8.83 mg/cm 2 ) exhibits high areal specific capacity of 0.522 mAh/cm 2 (4.24 F/cm 2 ) at 1 mA/cm 2 , and a long-term cycling stability (85.8% of capacity retention after 6000 charge-discharge cycles). This is mainly because N-doped rGO can increase specific area and electrical conductivity, enhance the electrochemical activity and effectively facilitate the electron/ion transport between the electrode and electrolyte. Besides, the quasi-solid-state hybrid supercapacitors (HSCs) assembled by the N-rGO/CS delivers a high volumetric specific capacity of 5.82 mAh/cm 3 at 1 mA/cm 2 , excellent energy density of 4.65 mWh/cm 3 under 10.5 mW/cm 3 and eminement cycle stability (87.6% retention over 6000 cycles at 10 mA/cm 2 ).