New insight on the mechanism of electrochemical cycling effects in MnO2-based aqueous supercapacitor

Abstract

The investigation of mechanism for electrochemical cycling process has become ever more important in supercapacitor electrode material for achieving higher stability and electrochemical performance. Herein, an electrochemical cycling effect has been demonstrated basing on the comprehensive study on the morphological and electronic evolution, which provides an insight into the capacity fluctuation mechanism in a typical MnO2-based supercapacitor. The results reveal that the significant changes of morphologies and chemical valence state of MnO2 take place accompanying with the intercalation of electrolyte ions (i.e. Na+) during the electrochemical cycling process. A structural reconstruction model is established to unravel the origin of microscopic changes of MnO2@carbon nanotubes (MnO2@CNTs) composites electrode and their relationships with the capacity at different electrochemical stages. It was found that the morphological and structural evolution of the electrode should be attributed to the dissolution-redeposition process of MnO2, which governed by the cation distribution near the interface between electrode and electrolyte. The ion intercalation-deintercalation process is evidenced by the oxidation state variations of Mn with the Na+ intercalation amount. Therefore, the capacity performance of MnO2@CNTs was strongly correlated with its structural and chemical states. This work will open up new perspectives for the capacity performance improvement of MnO2-based electrode materials.