High energy-power density Zn-ion hybrid supercapacitors with N/P co-doped graphene cathode

By combining the large power density of supercapacitors with the high energy density of ion batteries, a novel zinc-ion hybrid supercapacitor (ZHSC) is proposed and considered a promising candidate. But there are still challenges in the selection and application of reliable cathode materials. Herein, we used a mature and safe one-step hydrothermal method to synthesize N/P co-doped graphene (NPG), which exhibited a unique three-dimensional structure and a large specific surface area, showing great advantages as cathode to assemble Zn//NPG ZHSC with zinc foil. In the 1 M ZnSO4 solution, the ZHSC shows superior electrochemical performance, which presents an excellent specific capacitance of 210.2 F g−1 under a wide working voltage of 1.8 V, and it achieves both a maximum energy density of 94.6 Wh kg−1 and a large power density of 4500 W kg−1. More importantly, the capacitance retention rate remains 82% and a coulomb efficiency of ∼100% is achieved after 15,000 cycles. Overall, the results of this study highlight the efficient synthesis and excellent performance of NPG cathode materials, and also promote the rapid development and great application of high-performance Zn-ion hybrid capacitors. •The N/P co-doped graphene shows a high specific capacitance in ZnSO4 solution.•Zn-ion hybrid supercapacitor is assembled by Zn//ZnSO4//NPG.•The excellent energy and power density of Zn//ZnSO4//NPG are achieved.