P-doped S vacancy-rich NiCo2S4 hollow microspheres for high-performance supercapacitors

P-doped S vacancy-rich NiCo2S4 hollow microspheres (P-NiCo2S4-x HMSs) were prepared by hydrothermal, sulfuration, and phosphorization methods. P doping and S vacancy dual defects can be simultaneously obtained during the phosphorization process. The dual defects can modulate the electron structure and create abundant electrochemical sites, boosting electron transfer and reaction kinetics. Theoretical calculations illustrated that the dual defects could reduce the adsorption energy of OH− and Mulliken charges of Ni atoms, in favor of OH− adsorption. The hollow construction can increase the specific surface area, promote ion diffusion, and alleviate the volume variation during charge/discharge processes. The specific capacity and rate capability of the P-NiCo2S4-x HMSs electrode can reach up to 1146.0 C g−1 at 1 A g−1 and 61.8 % at 30 A g−1, respectively. The P-NiCo2S4-x HMSs electrode exhibited remarkable cycling stability with a 79.5 % capacity retention after 20,000 consecutive charge/discharge cycles. The assembled P-NiCo2S4-x//AC hybrid supercapacitor manifested an infusive energy density of 62.7 Wh kg−1 at 867 W kg−1.