Si-Based Nanostructured Arrays As Anodes For Lithium-Ion Batteries:Synthesis,Characterization, And Application

Graphite is widely used as the commercial anode materials for lithium-ion batteries, however, it has a relatively low theoretical capacity (372mAhg-1), which can’t meet the demand of ever-increasing portable energy storage device. As such, the development of new lithium-ion battery anode materials has made significant progress over the past decades. Since its theoretical capacity is about ten times larger than that of graphite, together with several features of a lower lithium intercalation potential, sufficient abundance, and friendly environment, silicon becomes one of the most promising alternatives of graphite for anode material. However, its practical use is limited by comparatively poor capacity retention and irreversible morphological change due to mechanical degradation caused by large changes in volume associated with lithiation and delithiation (～400%) during cycling, which becomes the biggest obstacle for silicon as the anode materials for lithium-ion battery.In order to improve cycling performance of silicon, we have modified material in two aspects by using nanotechnology and compositing:First, synthesis of Si and Si/C composite nanotube arrays with ZnO nanorod arrays as sacrificial templates; Second, modification of NiSix/Si nanorod arrays with carbon, germanium, and iron oxide.1. Sealed Si and Si/C composite nanotube arrays were successfully prepared by chemical vapor deposition (CVD) with ZnO nanorod arrays as sacrificial templates. The influence of wall thickness of the silicon nanotubes and the carbon shells was also investigated on the performance of lithium-ion battery. This result showed that the Si nanotube arrays with less wall thickness retained more than30%of the initial reversible discharge capacity after100cycles with only60%of the initial Coulombic efficiency, and were significantly better than the thick-walled ones on cycling performance. In addition, the carbon shells coated on the surface of the silicon nanotube arrays imporved the initial Coulombic efficiency up to about70%with57%of the initial reversible capacity after300cycles.2. We have developed a combination of CVD and RF sputtering method to fabricate NiSix/Si, NiSix/Si/C, NiSix/Si/Ge, and NiSix/Si/Fe2O3nanorod arrays as anodes for Li-ion batteries. The arrayed NiSix/Si nanorods showed a initial discharge capacity of about2500mAhg-1with initial Coulombic efficiency of only about60%. NiSix/Si/C core-shell nanorod arrays showed the best cycle performance among all of these samples, which retained the reversible capacity of about50%after100cycles. However, this material exhibited the initial Coulombic efficiency of only40%. NiSix/Si/Ge core-shell nanorod arrays show the worst cycling performance among these samples, and retained the initial reversible capacity of30%after100cycles. In addition, NiSix/Si/Fe2O3core-shell nanorod arrays had the highest initial Coulombic efficiency of around80%, but its cycling performance is the same as NiSix/Si/Ge core-shell nanorod arrays.