Sandwich-structured carbon nanofiber/MnO2/carbon nanofiber composites for high-performance supercapacitor.

• Sandwich-structured C/Mn/C with a triple layer were fabricated by electrospinning. • Well-preserved MnO 2 NPs in the interlayer are utilized as electroactive sites. • Hollow core present in the interlayer serves as an excellent conductive network. • Symmetric C/Mn(10)/C electrode showed high specific capacitance and long cycle life. • Asymmetric C/Mn(10)/C offers high energy density in a high potential window. Sandwich-structured carbon nanofiber/MnO 2 /carbon nanofiber composites with a triple layer are fabricated by electrospinning. The optimized sandwich-structured composite electrodes exhibit the maximum specific capacitance of 220 F/g at 1 mA/cm2, a high energy density of 24.63 Wh/kg at a power density of 400 W/kg, and an excellent retention rate of 94% after 10,000 cycles. The stable spatial distribution of MnO 2 nanoparticles between the upper and lower carbon nanofiber webs allowed full use of the well-preserved MnO 2 nanoparticles in the interlayer as electroactive sites, providing better electrochemical performance. Furthermore, the hollow core present in the interlayer serves as an excellent conducting network, providing a short ion diffusion path for both ions and electrons. In addition, the asymmetric supercapacitor shows excellent cycling behavior between 0 and 1.4 V and a large energy density of 44.3 Wh/kg at a power density of 400 W/kg, showing great potential in the development of energy storage devices with high energy density for practical applications. [ABSTRACT FROM AUTHOR]