Study Of Novel Silicon-Based Anode Materials For Lithium-Ion Batteries

Silicon has been considered as one of the most promising anode materials in lithium-ion battery(LIBs)for replacing graphite materials due to its extremely high theoretical specific capacity(about 4200 mAh g-1)and abundance.However,the large volume expansion(approximately 400%)and poor electrical conductivity of silicon during the cycle have prevented its application in the field of lithium ion batteries.In order to solve these two problems,in this paper,carbon is introduced,and carbon is compounded with silicon to prepare Si/C composite material to increase the conductivity of the material.At the same time,in order to alleviate the volume effect of silicon,the structure of two kinds of Si/C composite materials is designed in this article:One is an egg-stacking-like Si/C composite material(ES)with the yolk-shell structure;the other is a Si/C composite material with a core-shell structure.The results are followed:(1)A novel Si/C composite with egg-stacking-like structure is designed and manufactured using nano silicon as raw material,silica as sacrificial layer,and polydopamine and phenolic resin as internal and external carbon shell after carbonization.It is found that an egg-stacking-like Si/C composite(ES)anode with spherical air holes was fabricated to gather the yolk-shell particles in a 3D carbon network with abundant channels allowing electrolyte to enter the material,which can facilitate the cycling performance.The half-cell battery assembled with these anodes presents high capacity and good rate performance,with a capacity reduction of only 27%per current density.And the cycling performance of ES anode is also praiseworthy that it delivers a high reversible discharge capacity of 2175 mAh g-1 after 300 cycles at 0.5 A g-1.(2)The anode material(Si@SiOxCy)with core-shell structure was formed by hydrophilic treatment of the surface of nano silicon,then grafting and carbonization via vinyl chain.During the cyclic process,the silicon-oxygen-carbon layer can not only support the volume expansion and contraction of silicon and prevent the silicon from the crushing and pulverization,but also improve the conductivity of the silicon-based anode material and reduce the resistance of Li+and electron transport.When used as an anode material,it exhibits good electrochemical performance.The Si@SiOxCy anode material maintains a reversible discharge capacity of 1169 mAh g-1 after 119 cycles at 0.5 A g-1,and 91.36%of the capacity is reserved.The capacity of 661.8 mAh g-1 was retained after 150 cycles at a high current density of 2 A g-1.