Tremella-like N,O-codoped hierarchically porous carbon nanosheets as high-performance anode materials for high energy and ultrafast Na-ion capacitors

摘要

AbstractTremella-like hierarchically porous carbon nanosheets (HPCNS) with a carbon interlayer distance of 0.41nm have been simply prepared via hydroxyapatite/KOH-synergetic pyrolysis of low-cost cattle bone at 550°C. The HPCNS possesses high surface heteroatom content (17.1at% oxygen and 6.4at% nitrogen) due to the low-temperature thermal treatment. The HPCNS that is tested in half-cell against metallic Na can deliver a high reversible capacity of 198.5mAhg?1after 1000 cycles at the current density of 0.7Ag?1, and maintains a capacity of 150.8mAhg?1even after 10,000 cycles at the current density of 7Ag?1. The further characterization shows that the superior rate performance and the unparalleled long-term cycling stability are attributed to the capacitive storage features of HPCNS and additional Na-ion storage via reversible formation and decomposition of metallic Na in HPCNS. Consequently, the Na-ion capacitor based on the HPCNS anode delivers integrated high energy and power densities (105.2Whkg?1at 0.07kWkg?1, 32.5Whkg?1at an ultrahigh power density of 60.4kWkg?1), as well as good long-term cycling stability (85.8% of the capacitance retention after 4000 cycles at the current density of 3.5Ag?1).Graphical abstrac