Phosphorus-doped Ni-Co sulfides connected by carbon nanotubes for flexible hybrid supercapacitor

As promising electrode materials for supercapacitors, nickel-cobalt bimetallic sulfides render the advantages of abundant redox reactions and inherently high conductivity. However, in general, unsatisfactory performance of low specific capacity, low rate capability, and fast capacity loss exist in Ni-Co sulfide electrodes. Herein, we rationally regulate phosphorus-doped nickel-cobalt sulfides (P-NCS) to enhance the electrochemical performance by gas-solid phosphorization. Moreover, carbon nanotubes (CNTs) as conductive additives are added to improve the cycle stability and conductivity and form the composite P-NCS/C/CNT. According to density functional theory, more electrons near the Fermi surface of P-NCS are demonstrated notionally than those of simple CoNi2S4. Electrochemical results manifest that P-NCS/C/CNT exhibits superior electrochemical performance, e.g., high specific capacity (932.0 C center dot g(-1) at 1 A center dot g(-1)), remarkable rate capability (capacity retention ratio of 69.1% at 20 A center dot g(-1)), and lower charge transfer resistance. More importantly, the flexible hybrid asymmetric supercapacitor is assembled using P-NCS/C/CNT and activated carbon, which renders an energy density of 34.875 W center dot h center dot kg(-1) at a power density of 375 W-kg(-1). These results show that as-prepared P-NCS/C/CNT demonstrates incredible possibility as a battery-type electrode for high-performance supercapacitors.