الفهرس 
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Abstract
In this work,Co9-xNixS8 nanoparticles with different Ni extents (x=2.6, 3 and 3.4) were prepared by a facile solvothermal method, followed by heat treatment at 400 ºC for 2 h.
The x-ray diffraction patterns with match X’PertHighScore program, showed single phase Co9S8 for the samples x=2.6 and 3.4, implying the integration of Ni ions into the Co9S8 lattice substituting Co ions mainly at octahedral sites.While the results of sample (x=3.0) revealed two phases Co9S8 (90.7%) and Co3O4 (10.3%) suggesting that some Co ions were segregated forming the oxide phase.
HRTEM images disclosed homogeneous particle morphology of sample (x=2.6) with an average size " ~ "75 nm. The SAED pattern showed the exact number of rings corresponding to the indexed crystallographic planes of the cubic Co9S8 phase.
XPS measurements indicated that Ni3+cations were only existed in the structure of Co6.4Ni2.6S8, while Ni2+ and Ni3+cations were located in the Ni-rich samples at x=3.0 and 3.4.FTIR absorption bands of NiS bonds around 668 and 1036 cm−1showed larger broadening with increasing Ni content.
SEM images of Co6.4Ni2.6S8 revealed clusters of nanospheres that are coated with nanoplatelet carbon sheets.
The bandgap energy of Co9-xNixS8 nanoparticles is gradually decreased with increasing Ni content. The sample with the lowest Ni content (x=2.6) displayed the highest refractive index (n) due to its good crystallinity and high density in comparison with other samples.
The intensity of photoluminescence (PL) spectra for x=3.0 was the highest emission due to the presence of secondary phase Co3O4 which increases the number of defect levels for trapping more excited electrons and preventing their rapid recombination with holes.
The CV study of the Li/Ni@Co9S8 battery confirmed the intercalation of Li + ions into Ni@Co9S8 material by observing three shallow peaks at 1.25, 1.8 and 2.5 V which indicating the formation of Co metal, Ni metal and various lithiated species e.g., Li2S and LixNi@Co9S8, respectively. Moreover, the developed nano-Ni@Co9S8 anode achieved the highest discharge capacity" ~ " 1660 mAhg− 1 for Li + ions storage at slow current density 0.5Ag-1. With respect to supercapacitor application, the assembled asymmetric cell of Ni@Co9S8 displayed the maximum specific capacitance " ~ "363 F g− 1 at scan rate 5 mV s − 1 and the minimum value " ~ "87.5 F g− 1 at 100 mV s − 1 owing to the weak diffusion of ions at higher scan rate. Furthermore, the investigated supercapacitor revealed long lifespan with 99% capacitance retention between cycles 1600 and 2000 by delivering about 200 F g− 1 after 2000 cycles.