Superior electrochemical performances of double-shelled CuO yolk-shell powders formed from spherical copper nitrate-polyvinylpyrrolidone composite powders

Spherical copper nitrate-polyvinylpyrrolidone (PVP) composite powders coated with a copper nitrate hydroxide [Cu₂(OH)₃NO₃]-carbon composite are prepared by a one-pot spray pyrolysis process. In this, Cu₂(OH)₃NO₃ and carbon are formed by dehydration of copper nitrate and carbonization of PVP, respectively. Thermal decomposition of the composite powders is then performed at 300 °C under an air atmosphere, producing the final yolk-shell-structured CuO powders. The electrochemical properties of these powders are then compared with those of commercial CuO nanopowders. The discharge capacities of the CuO yolk-shell powders and the commercial CuO nanopowders after 240 cycles at a current density of 500 mA g^-1 are 590 and 302 mA h g^-1, respectively. Furthermore, the discharge capacity of the CuO yolk-shell powders is as high as 615 mA h g^-1, even after 1000 cycles at a current density of 1000 mA g^-1. Electrochemical impedance spectroscopy reveals that the structural stability of the CuO yolk-shell powders during cycling lowers the charge transfer resistance, and thereby improves the lithium ion diffusion rate.