The development of flexible electrochemical devices with high-density electrochemical capacitive energy storage and high mechanical strength remains the main obstacle for practical applications. Here, we designed and generated a S/N co-doped graphene based electrode (CoS1.097/GF electrode) with welldistributed CoS1.097 nanoparticles (NPs), which were anchored directly in/on porous carbonized melamine foam by a squeeze-dip-coating and sulfidation process. The CoS1.097/GF electrode shows desired conductivity, cycling stability and high ion-accessible surface area, leading to an ultrahigh specific capacitance of 4476 F g-1 at a current density of 1 A g-1 and a favourable rate capability of 87.1% at 10 A g-1. Furthermore, a high-strength and flexible CoS1.097/GF/KOH/PVA composite film electrode was prepared using KOH/polyvinyl alcohol (KOH/PVA) as a gel electrolyte, and a flexible CoS1.097/GF||GF asymmetric electrochemical capacitor (a-EC) device was produced with a high energy density of 33.2 W h kg-1 at a power density of 374.7 W kg-1, where the KOH/PVA gel works as a solidstate electrolyte and separator. We observed 95.6% capacitance retention after 10 000 cycles within the potential window of 0–1.5 V. Notably, we confirmed that the CoS1.097/GF||GF a-EC device performed at large bending angles (from 0 to 180), and was able to be twisted into various shapes, indicating its potential for application in wearable and portable electronic devices.