Engineering of N, P co-doped hierarchical porous carbon from sugarcane bagasse for high-performance supercapacitors and sodium ion batteries

Porous carbon is one of the most promising electrode materials for energy conversion and storage devices due to its high specific surface area, low cost, sustainability, appropriate charging/discharging voltage platform and high interlayer spacing. However, the disadvantage of insufficient energy storage capacity frustrates its wide applications. Herein, a novel N, P co-doped porous carbon derived from sugarcane bagasse (SBNPk) was prepared by hydrothermal method combined with KOH activation and carbonization, and was applied to supercapacitors (SCs) and sodium-ion batteries (SIBs). The SBNPK possesses a special hierarchical porous structure, improved surface area, larger interlayer spacing, and moderate N, P doping level. Specifically, the SBNPk carbonization at 600 °C (SBNPk-600) exhibits the highest specific capacitance (356.4 F g−1 at 1 A g−1), good rate capability and excellent cycle stability (5% loss over 10,000 cycles) in a three-electrode system. Further assembled in a symmetrical two-electrode system, the SBNPK-600//SBNPK-600 can still provide a higher energy density of 6.5 Wh kg−1 at 251.9 W kg−1 and superior cycle performance (96.5% of capacitance retention at 2 A g−1 after 20,000 cycles). Surprisingly, the SBNPK-600 as an anode for SIBs also delivers a high reversible capacity of 304.1 mAh g−1 at 25 mA g−1 and excellent cycle performance (225.7 mAh g−1 after 1000 cycles at 500 mA g−1), indicating its superior sodium storage capability. This work provides a simple and new way to enhance the electrochemical performance of biomass waste-derived carbon by heteroatom doping, which is helpful to further boost its application in the field of energy storage.