Transforming Single-Crystal CuO/Cu₂O Nanorods into Nano-Polycrystalline Cu/Cu₂O through Lithiation

One-dimensional single-crystal CuO/Cu₂O nanorods were fabricated by controlled oxidation of a copper substrate and examined as the active material in porous anodes for lithium-ion batteries. Electrochemical testing against Li-metal revealed that using sodium carboxyl methyl cellulose (CMC) as the binder enabled an excellent capacity retention for 50 cycles, while the use of polyvinylidene fluoride (PVDF) resulted in a continuous capacity fade. Transmission electron microscopy illustrated the phase composition and morphological changes throughout cycling, revealing that for both types of binders, lithiation of CuO and Cu₂O disrupted the single-crystal nanorod structure, producing multiple Cu/Cu₂O nanograins within the rods. With continuous cycling the average grain size of these nanocrystals decreased. A significant difference between the CMC and PVDF binder electrodes was the irreversible formation of LiCuO during delithiation for the PVDF case, which can explain the continuous capacity fade. Scanning electron microscopy also revealed microcracks throughout the electrode surface when the PVDF binder was employed.