Self-supported Nanostructured Cobalt Oxide As Anode Materials For Lithium Ion Batteries

Lithium storage of the anode is one of the key technologies to develop high-performance Li ion batteries (LIBs). Although the traditional graphite anode materials exhibit excellent cycle stability and charge/discharge performance, its low specific capacity cannot satisfy the ever-growing demand for high-energy batteries. Thus it is critical to explore new anode materials to replace the graphite anode. Cobalt oxide, one of the transition metal oxides, is considered as a promising anode materials due to its high theoretical capacity. However, the large irreversible capacity in the first cycle and fast fading capacity have been blocking its practical use in the LIBs. In this thesis, we successfully synthesized self-supported Co3O4 nanowires, C-Co3O4 yolk-shell nanowires and (Co3O4, CoO) nanosheets on Ni foam substrate based on hydrothermal method. The detail research contents are summarized as following:1. The Co2(CO3)(OH)2 nanowires were grown on the Ni foam first via hydrothermal method, and then the Co3O4 nanowires were obtained after the precursor nanowires were annealed in the air. The nanowire arrays exhibit a high first discharge capacity of 1300 mAhg-1, while its cycle stability is relatively low.2. The C-Co3O4 yolk-shell nanowires were synthesized by using the Co2(CO3)(OH)2 nanowires as the template and the Al2O3 layer as a sacrificed layer by the combination of ALD and CVD method. The as-prepared C-Co3O4 NWs exhibit excellent cycle performance of 1000 mAhg-1 after 20 cycles.3. The cobalt oxide nanosheet arrays were prepared by two different methods. One is to synthesize cobalt hydroxides nanosheets on Ni foam first with one-pot hydrothermal and then the Co3O4 nanosheets can be obtained after annealing the precursor nanosheets in the air. The as-grown nanosheets have a high capacity and good stability. The other is to coat a thin layer iron oxide on the Co2(CO3)(OH)2 nanowires with ALD technique. After annealed in Ar, the nanowires were assembled into the nanosheets. The nanosheets assembled from nanowires exhibit better electrochemical performance than the single nanowire arrays, with the irreversible capacity of 1078 mAhg-1 after 50 cycles.