The Preparation And Lithium Insertion-deinsertion Properties Of Si-based Nanomaterials

Lithium-ion battery is the most popular type of battery used in portable electronics. Currently, the commercial lithium-ion battery anode materials are carbonaceous materials, but their low storage capacity limit their use due to the increased demand of mobile power supply. Silicon is one of the most promising anode materials because it has the highest known theoretical charge capacity and is the second most abundant element on earth. However, Silicon anodes have limited applications because of the huge volume change associated with the insertion and extraction of lithium. The large volume change causes cracking and pulverization of the anode, which leads to a loss of electrical contact and eventual fading of capacity. In this paper, we try to improve the lithium storage properties of Si through nanostructure and nanocomposites.Two-dimensional (2D) ultrathin Silicon nanosheets (Si NSs) have been successfully synthesized by DC arc discharge method. The2D ultrathin characteristic of Si NSs is confirmed by means of transmission electron microscopy (TEM), atomic force microscopy (AFM) and Raman. It is found that the2D size of the Si NSs is about20nm, with thickness less than2.5ran which is about8atomic layers. The characteristic Raman peak of Si NSs is found to have an appreciable (20nm) shift to low frequency, presumably due to the size effect. Electrochemical tests show that the contents of conductive agent, the types of conductive agent and the cutoff voltage have effect on the cycling performances of the Si NSs anode. When the Si NSs used as lithium-ion battery anode material, it shows a reversible capacity of441.7mAh g-1after40cycles. When the current density increased, the capacity decreased. But, as the current density changes into the initial value, the capacities get back to the initial level.DC arc discharge method was used to fabricate Si-SiC-Ni nanocomposites. From the TEM images, it can be found that the composites are made of winded nanowires. In this system, Ni acted as catalyst to grow nanowires through VLS mechanism. When the nanocomposites used as lithium-ion battery anode material, it shows improved cycling performance compared with pure Si nanomaterials. SiC, a kind of inactive material, can buffer the volume change during cycling process. After5cycles, the columbic efficiency can always be kept above96%, the reversibility is very good. After35cycles, the reversible capacity is598mAh g-1, which is1.6times of the traditional carbon materials.