Binder-free Co–CoOx nanowire arrays for lithium ion batteries with excellent rate capability and ultra-long cycle life

Abstract

Structure stability and fast charge–discharge capacity are highly desirable for electrode materials applied in lithium ion batteries (LIBs). In this report, binder-free Co–CoO_x nanowire arrays (NWAs) were obtained by a simple H₂ reduction of Co₃O₄ NWAs. The resulting Co–CoO_x NWAs were grown directly on the current collector with enough open space between each nanowire, which provides fast charge transfer channels and large accessible surface area to the electrolyte. More importantly, the introduction of electrochemically inactive Co without volume change during cycling for LIBs could improve the structural stability of the Co–CoO_x NWA electrode and the high electronic conductivity of metallic Co in the array structure greatly enhances the electron transfer ability of Co–CoO_x nanowires. Benefitting from those designed structural features, the binder-free Co–CoO_x NWAs achieved remarkable electrochemical performances with excellent cycle stability at high rates and high rate capacity. The Co–CoO_x NWA electrode maintains highly stable capacities of 990 and 740 mA h g⁻¹ after 1000 cycles at 10 and 20 A g⁻¹, respectively. At an ultrahigh rate of 50 A g⁻¹, a high reversible capacity of 413 mA h g⁻¹ is achieved. The result demonstrates that such a novel Co–CoO_x nanowire array structure is a new strategy to design high performance anode materials for LIBs.