Porous CuO nanowires as the anode of rechargeable Na-ion batteries

We report the preparation of porous CuO nanowires that are composed of nanoparticles (∼50 nm) via a simple decomposition of a Cu(OH)2 precursor and their application as the anode materials of rechargeable Na-ion batteries. The as-prepared porous CuO nanowires exhibit a Brunauer-Emmett-Teller (BET) surface area of 13.05 m2·g−1, which is six times larger than that of bulk CuO (2.16 m2·g−1). The anode of porous CuO nanowires showed discharge capacities of 640 mA·h·g−1 in the first cycle and 303 mA·h·g−1 after 50 cycles at 50 mA·g−1. The high capacity is attributed to porous nanostructure which facilitates fast Na-intercalation kinetics. The mechanism of electrochemical Na-storage based on conversion reactions has been studied through cyclic voltammetry, X-ray diffraction (XRD), Raman spectroscopy, and high resolution transmission electron microscopy (HRTEM). It is demonstrated that in the discharge process, Na+ ions first insert into CuO to form a Cu 1− II Cu I O1−x/2 solid and a Na2O matrix then Cu 1− II Cu I O1−x/2 reacts with Na+ to produce Cu2O, and finally Cu2O decompose into Cu nanoparticles enclosed in a Na2O matrix. During the charge process, Cu nanoparticles are first oxidized to generate Cu2O and then converted back to CuO. This result contributes to the design and mechanistic analysis of high-performance anodes for rechargeable Na-ion batteries.