Electrochemical properties of core-shell structured NiO@SiO₂ ultrafine nanopowders below 10 nm for lithium-ion storages

Ultrafine core-shell NiO@SiO₂ nanopowders with various shell thicknesses were prepared by one-pot flame spray pyrolysis. The mean diameters of the NiO nanoparticles with 0, 2, and 5 wt% SiO₂ were 13, 10, and 9 nm, respectively. The coating of the NiO nanopowders with amorphous SiO₂ was confirmed by transmission electron microscopy, zeta potential analysis, and X-ray photoelectron spectroscopy. The initial discharge capacities of the NiO nanopowders with 0, 2, and 5 wt% SiO₂ at a current density of 1 A g^-1 were 1123, 1165, and 1145 mA h g^-1, with corresponding initial Coulombic efficiencies of 66, 63, and 69%, respectively. The discharge capacities of the NiO nanopowders with 0, 2, and 5 wt% SiO₂ after 150 cycles were 440, 669, and 554 mA h g^-1, with capacity retentions from the second cycle of 58, 74, and 68%, respectively. The structural stability of the core-shell NiO@SiO₂ nanoparticles during repeated Li charging and discharging improved the cycling and rate performances of the electrodes as compared with those containing bare NiO nanopowders.