The Modification Of Nano-Si As Anode Of Lithium Ion Battery

The theoretical capacity of silicon anode material of lithium-ion battery is up to 4200 mAh g^-1. However, this material undergoes the pulverization arising from its volume expansion and contraction during lithium insertion and extraction, which greatly hinders its commercial application. Although nanoscale Si will reduce the internal stress of particles to some extent, the nanomaterial is easy to aggregate and has poor conductivity, so its electrochemical performance is not satisfied. In this paper, we applied diazotization reaction to modifiy nano-Si to produce Si-PhCOO-Ag and Si-Ph-G composite materials, the resulting composites exhibited excellent electrochemical performance. XPS, TEM and other testing methods were used to characterize the microstructure of composite materials. Galvanostatical charge-discharge and cycle voltammetry was implemented to test their electrochemical characteristics.For the Si-PhCOO-Ag composite, the Si and Ag particles were distributed uniformly, in which Ag nanoparticles were fixed on the silicon surface by PhCOO-functional group, thus improving the conductivity of the silicon anode. When the current density is 1000 mA g^-1, its delithiation capacity could remain at 500 mAh g^-1 after 50 cycles. In addition, from a series of comparative experiments between Si-PhCOO-Ag and Si-Ag, we can draw a conclusion that the diazotization reaction played an important role in ensuring the advantages of both structure and properties.Based on the same principle, we prepared the Si-Ph-G composite material by two-step diazotization reactions. In this material, nano-Si particles were dispersed in graphene sheets uniformly, in which nano-silicon and graphene were connected by Ph-functional group. It is noteworthy that the reduction methods of GO had a significant impact on the performance of the product. This material also showed good electrochemical performance. After 50 cycles, its reversible capacity could keep at 570 mAh g -1 at the current density of 1000 mA g^-1. The result of TG tests proved that the mass fraction of graphene was about 20 wt% in the composite.