High-performance 2.5 V supercapacitor with high energy density and long cycling stability based on graphene coated oxygen-vacancy birnessite

Because carbon based supercapacitor electrode has low energy density, so birnessite electrode material has attracted more and more attention due to its low cost, environmental friendliness, high oxygen evolution potential and high theoretical specific capacitance. In this work, novel nanoneedle-like rGO/V-NaxMnO2/CC cathode material with oxygen vacancies has been prepared, where rGO and CC represent reduced graphene oxide and carbon cloth, respectively. By using surface-protection strategy and introduction of abundant oxygen vacancies, high capacitance of rGO/V-NaxMnO2/CC is obtained with 362.5 F g−1 at 1 A g−1. After the current density increases to 24 A g−1, the capacitance retention is 56.56%, presenting excellent rate performance. In addition, after 10,000 charge/discharge cycles at 5 A g−1, the capacitance retention rate is 90.17%, showing excellent cycle stability. The aqueous asymmetric supercapacitor (ASC) of ACMK-3 // rGO/V-NaxMnO2/CC has a wide potential window of 0 ~ 2.5 V. And the energy density is as high as 72.2 Wh kg−1 at 1254 W kg−1. After 10,000 charge-discharge cycles at 4 A g−1, the ASC still remains a capacitance retention rate of 88.5%. This work provides a facial method to improve electrochemical properties and shed a light on fabricating a novel cathode for aqueous supercapacitors. ●The rGO/V-NaxMnO2/CC electrode with high specific capacitanceand high rate capability has been prepared.●The cover of rGO and introduction of oxygen vacancies make NaxMnO2/CC high specific capacitance and high rate capability.●ACMK-3//rGO/V-NaxMnO2/CC delivers a high energy density of 72.2 Wh kg−1 under the wide potential window of 0–2.5 V.