Two-dimensional β-MoO 3 @C nanosheets as high-performance negative materials for supercapacitors with excellent cycling stability.

MoO 3 has gained a great deal of attention as a promising electrode material in energy storage devices. In particular, the low dimensional MoO 3 nanosheets coated with carbon layers are desirable electrode materials in supercapacitors. However, the fabrication or construction of β-MoO 3 with a special morphology is difficult. Here, we report a simple solvothermal treatment method to synthesize two-dimensional β-MoO 3 @C (2D β-MoO 3 @C) nanosheets. When used as electrode materials for supercapacitors, the as-prepared material displays an ultra-long lifespan with a 94% retention ratio after 50 000 cycles at 2 A g -1 . The excellent cycling stability is mainly attributed to the unique 2D nanosheet structure and the presence of the carbon layer on the surface of the nanosheet. Specifically, the presence of the carbon layer increases the electric conductivity of MoO 3 , which facilitates a good access point for electrolyte ions and short ion diffusion paths. In addition, MoO 3 that has been coated with a carbon layer can maintain a good structural stability due to the carbon layer restricting the volume expansion of MoO 3 during the charge procedure. We believe that the present work opens a new way for designing the 2D layered materials with unique architectures for supercapacitor applications.