Novel rhombus-shaped Co3O4 nanorod (NR) arrays grown directly on a nickel substrate are successfully synthesized via a fluorine-mediated hydrothermal synthesis approach. The rhombic Co3O4 NRs have an average edge length of 400 nm, an induced edge angle of 50° and a length of 15 μm. The possible formation mechanism of the novel NR arrays was investigated by X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopies, and X-ray photoelectron spectroscopy. The formation of Co(OH)F plays a crucial role in the formation of the rhombus-shaped NR arrays. When tested as anodes for lithium ion batteries (LIBs) without the addition of other ancillary materials (carbon black and binder), the Co3O4 NR arrays on a nickel substrate exhibit a high reversible capacity (over 1000 mA h g−1) and good cycling performance over 20 cycles in the range of 0.005–3 V at a current rate of 1 C.
