Versatile electrochemical activation strategy for high-performance supercapacitor in a model of MnO2

Supercapacitors as an important component of sustainable energy system attract tremendous attention, but improvement of their performance in energy density and power capability is still considered as a challenging task. Herein, a versatile electrochemical activation strategy is introduced for a prototypical MnO2 film-coated carbon nanotubes (MnO2@CNTs) based electrode to boost its electrochemical energy storage performance. The electrochemical activation process was completed by an initial charge–discharge cycling operation, which led to the dense MnO2 film transforming into ultrathin three-dimensional (3D) nanosheets birnessite with an unexpected Na+ ions diffusion path. By adjusting electrochemical activation parameters, the nanostructure and intercalated Na+ content of birnessite was optimized. The electrochemical activated MnO2@CNTs-based supercapacitor showed a specific capacitance as high as ∼404 F g−1 at a current density of 0.5 A g−1, and about 78.7% of the initial capacitance was retained at a high current density of 100 A g−1. This should be ascribed to the optimized MnO2 3D nanosheets structure and uniformly embedded Na+ ions after electrochemical activation operations, which greatly enhanced the surface- and diffusion-controlled capacitance during the electrochemical cycling processes. It is believed that this work will provide a significant strategy for the development of high-performance supercapacitor electrodes.