Carbon nanofiber/cobalt oxide nanopyramid core-shell nanowires for high-performance lithium-ion batteries

Carbon nanofiber (CNF)/Co₃O₄ nanopyramid core-shell nanowires (NWs) are synthesized using an electrospinning method followed by reduction and hydrothermal treatment in order to improve the capacity, cycle stability, and high-rate capability of the electrodes in Li ion batteries (LIBs). The morphology, crystal structure, and chemical states of all samples are investigated by means of field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetric analysis. For comparison, conventional CNFs, octahedral Co₃O₄, and Co₃O₄/CNF composite electrodes are prepared. LIB cells fabricate with the CNF/Co₃O₄ nanopyramid core-shell NWs exhibit superb discharge capacity (1173 mAh g^-1 at the 1st cycle), cycle stability (795 mAh g^-1 at 50 cycles), high initial Coulombic efficiency (84.8%), and high-rate capability (570 mAh g^-1 at a current density of 700 mA g^-1) as compared to the conventional CNF, octahedral Co₃O₄, and Co₃O₄/CNF composite electrodes. The performance improvement is owing to the introduction of one-dimensional CNFs relative to efficient electron transport in the core region, extensive utilization of Co₃O₄ nanopyramids with high capacity grown closely on the CNFs in the shell region, and the network structures of the electrode relative to the improvement of Li ion diffusion.