Coral-Like Yolk-Shell-Structured Nickel Oxide/Carbon Composite Microspheres for High-Performance Li-Ion Storage...

In this study, coral-like yolk-shell-structured NiO/C composite microspheres (denoted as CYS-NiO/C) were prepared using spray pyrolysis. The unique yolk-shell structure was characterized, and the formation mechanism of the structure was proposed. Both the phase separation of the polyvinylpyrrolidone and polystyrene (PS) colloidal solution and the decomposition of the size-controlled PS nanobeads in the droplet played crucial roles in the formation of the unique coral-like yolk-shell structure. The CYS-NiO/C microspheres delivered a reversible discharge capacity of 991 mAh g^-1 after 500 cycles at the current density of 1.0 A g^-1. The discharge capacity of the CYS-NiO/C microspheres after the 1000th cycle at the current density of 2.0 A g^-1 was 635 mAh g^-1, and the capacity retention measured from the second cycle was 91%. The final discharge capacities of the CYS-NiO/C microspheres at the current densities of 0.5, 1.5, 3.0, 5.0, 7.0, and 10.0 A g^-1 were 753, 648, 560, 490, 440, and 389 mAh g^-1, respectively. The synergetic effect of the coral-like yolk-shell structure with well-defined interconnected mesopores and highly conductive carbon resulted in the excellent Li⁺-ion storage properties of the CYS-NiO/C microspheres.