Oxygen vacancies refilling and potassium ions intercalation of δ-manganese dioxide with high structural stability toward 2.3 V high voltage asymmetric supercapacitors.

Oxygen vacancies occupation and coordination environment modulation of the transition-metal based electrodes are effective strategies to improve the structural stability and electrochemical performance. In this work, the 2-methylimidazole (2-MI) doped manganese dioxide (MnO) anchored on carbon cloth (CC) is fabricated via a simple method (MI-MnO/CC), where the oxygen defects on/inside the K doped δ-MnO nanosheets are in-situ created by reductive ethanol/Mn and occupied by 2-MI ligands. With the pre-embedded K ions and abundant ligand-refilled defects, the electronic coordination structure, structural stability and electron/ion diffusion efficiency can be effectively enhanced. Therefore, the MI-MnO/CC reveals a remarkable specific capacitance of 721.2 mF cm with excellent cycle durability (capacitance retention of 93.4% after 10,000 cycles) under 1.3 V operation potential window. In addition, an asymmetric supercapacitor assembled by MI-MnO/CC and activated mechanical exfoliated graphene oxide yields a maximum energy density of 57.0 Wh kg and a highest power density of 23.0 kW kg under 2.3 V. This effective oxygen defect stabilization strategy by ligands refilling can be extended to various metal oxide-based electrodes for energy storage and conversion.