A novel Fe-Co-S/P electrode for aqueous symmetric supercapacitors

Developing electrode materials with high specific capacitance within both positive and negative potential window is an effective way to obtain aqueous supercapacitors with high energy density. In this work, P doped Fe-Co-S binary metal sulfides (Fe-Co-S/P) was demonstrated to show high specific capacitance within a wide potential window from − 1–0.55 V. When used as cathode, it exhibited a specific capacitance of 0.8 F cm ⁻² (320 F g ⁻¹). After 20,000 cycles at 20 mA cm ⁻², it even increased to 242.3% of the initial capacitance. When used as anode, it also had a specific capacitance of 1.34 F cm ⁻² (536 F g ⁻¹ ) and satisfied cyclic performance (71.4% of the initial capacitance after 20,000 cycles). Moreover, the symmetric supercapacitors (SSCs) assembled with the Fe-Co-S/P electrodes delivered high energy density of 106.42 Wh kg ⁻¹ at a power density of 800 W kg ⁻¹ and exhibited excellent cyclic stability by preserving 93.9% of the initial capacitance after 5000 cycles. This work not only establishes Fe-Co-S/P as a high-performance supercapacitor electrode material, but also provides a new strategy to design and construct high-performance aqueous SSCs.