Si/C Composite Anode For Lithium Ion Battery Prepared By Magnesiothermic Reduction And Their Electrochemical Performance

Silicon is a resource abundant,low cost anode material for lithium ion battery,which is much safer compared with the graphite material.But it experiences a tremendous volume change(>300%)during the lithiation and delithiation processes,which induces severe pulverization and subsequent electrical disconnection from the current collector,as well as continual formation of the so-called solid electrolyte interphase(SEI)on the Si surface newly exposed to the electrolyte.Both effects result in the performance degradation of silicon.In addition,the conductivity of silicon is low,in which lithium ion diffusion is quite slow,thus limiting the capacity utilization and rate performance.Silica(SiO2)has been considered to be the anode material because its low discharge potential.Besides,SiO2 is one of the most abundant materials on earth and the cost is cheaper than other materials.The electrochemical performance of SiO2 was not satisfied for the reasons of volume expansion effect and generating irreversible lithium silicate particles via the electrochemical reaction during cycling.Compositing silicon and silica with carbon will help to improve the conductivity of silicon and silica and the stability of their structures.In this paper,Na2SiO3 and glucose were used as the silicon and carbon source for the preparation of carbon/silica composite materials.And then carbon/silicon composite materials were obtained using magnesiothermic reduction.The ratio of raw materials and calcination temperature were adjusted for the preparation of the composite materials.Furthermore,the electrochemical performance of the obtained products was tested as anode for lithium ion batteries.The results show that the carbon/silica composite exhibits a favorable lithium storage performance with high reversible capacity and excellent rate-capability,which exhibits good cycling performance(a specific capacity of 434 mAh/g after the 50 th cycle at a current density of 100 mA/g)and high rate capability(187.4 mAh/g even at5A/g).Using NaCl as cooling agent can avoid the formation of Si C,and the carbon/silicon composite was obtained successfully.The Si/C composite delivers a high initial discharge capacity of 1953 mAh/g and charge capacity of 1123 mAh/g at the current density of 100 mA/g,as well as a Coulombic efficiency of 57.5%.But the capacity is rapidly decayed.While the NaCl was used as the template to prepare Si/Ccomposite with 3D porous structure,the cycle performance of Si/C composite was improved obviously,which delivers a capacity of 310 mAh/g after 50 cycles at the current density of 100 mA/g.