Preparation of N/S co-doped graphene/polypyrrole composites for binder-free flexible supercapacitors

Flexible electrodes have been extensively studied and developed, but how to maintain flexibility and increase capacitance at the same time is still challenging. In this work, nitrogen/sulfur co-doped reduced graphene oxide (RGO) and a series of polypyrrole (PPy) composite (RGP-i, i = 1, 2, 3, 4, 5, 6) aerogel materials are prepared by adjusting the mass ratio of graphene oxide (GO) and PPy and using thiourea (CS(NH2)(2)) as a reducing agent. Binder-free flexible electrodes are assembled by using carbon cloth (CC) as substrates. Among these samples, RGP-5 prepared with the ratio of m(GO):m(PPy) = 1:1 exhibits excellent comprehensive electrochemical performance, with high specific capacitance (394 F g(-1) at 1 A g(-1)) and high capacitance retention (55.4% from 1 to 20 A g(-1)) simultaneously. The assembled RGP-5//RGP-5 flexible quasi-solid symmetric supercapacitor shows an energy density of 6.25 Wh kg(-1) at a power density of 500 W kg(-1), and a power density of 2501 W kg-1 at an energy density of 4.37 Wh kg(-1). After 1000 cycles of charging and discharging, its capacitance can maintain 80%. The specific capacitance of RGP-5//RGP-5 under different bending angles is almost unchanged, indicating that it shows good flexibility.