Cu/Cu2O@Ppy nanowires as a long-life and high-capacity anode for lithium ion battery

A core-shell structure polypyrrole coated Cu/Cu2O (Cu/Cu2O@Ppy) nanowires was synthesized by a facile hydrothermal method. Benefiting from the nanowire morphology, the confinement effect of Ppy shell and the modification of Cu metal, the Cu/Cu2O@Ppy as the anode of lithium ion battery exhibits an increased reversible capacity of 787 mAh g(-1) under the current density of 0.1 A g(-1) after 250 cycles. In addition, a good long-life rate capacity also can be obtained (401 mAh g(-1) at 1 A g(-1) after 500 cycles). More to the point, the increased capacity of Cu/Cu2O@Ppy nanowires is explained by the analysis of capacity differential curve, ex-situ X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy. It was demonstrated that the constant formation of solid electrolyte interface film and the transformation of Cu to Cu2O lead to the increased capacity in the initial cycles. Furthermore, a phase transformation of host material from Cu2O to CuO is proved to be the main reasons for the subsequent cycles of capacity increase. This in-situ phase transformation of electrode material provides a novel perspective for the increased capacity phenomenon of metal compounds in lithium ion battery.