Preparation And Electrochemical Performance Of Nano-silicon/carbon Composite Materials

Environmental and energy issues have become two major challenges facing mankind,and exploring and researching renewable energy and clean energy to replace traditional fossil energy has become one of the important strategies for sustainable development.Li-ion battery has been widely used in portable electronic equipment and power vehicle,due to its excellent performance including high capacity,long life,flexible design and friendly environment etc.At present,most of the anode materials for lithium-ion batteries are graphite materials with low theoretical lithium storage capacity,and its research has already approached the theoretical capacity difficult to have breakthrough,therefore,it is imperative to study new electrode materials with high specific capacity.Silicon,has the advantages of high theoretical specific capacity(4200 mAh/g),abundant reserves and friendly environment,is expected to replace graphite anode materials.However,the severe volume change of silicon anode material in the process of charge-discharge is the key factor for limiting its application in high-capacity lithium ion batteries.Carbon materials are often used as "buffer matrix" to form composite electrode materials because of their excellent electronic conductivity,great ductility and good structural stability in the process of charge-discharge.In addition,the intercalated-Li potential of silicon material and carbon material is similar,and it is hoped to combine with the advantages of both materials to create a new type of lithium ion battery anode material with high capacity and good cycle performance.In this paper,nano-silicon particles were used as silicon source and modified,then graphene oxide(GO)and glucose were used as carbon source to prepare as silicon-carbon composite anode materials by different processes follows.(1)Silicon-graphene areogel composite anode material was prepared by hydrothermal reduction reaction with graphene oxide as carbon source.The results show that the dispersion of silicon particles and graphene is uniform in the three-dimensional porous structure morphology of the composites.When the mass ratio of graphene is 12.5%.The first discharge specific capacity is 2520 mAh/g,after 100 cycles,the discharge specific capacity is still 1337 mAh/g,and the capacity retention rate is 53%.This is due to the existence of three-dimensional porous and interlaced graphene aerogels,which can improve the electronic conductivity of the materials,and the porous structure is beneficial to the penetration of electrolyte.In addition,the volume effect of silicon particles can be effectively limited with the exist of graphene aerogels to keep the stability of silicon materials in charge-discharge cycle.(2)Different concentrations of phosphorus-doped silicon(P-Si-60)nanoparticles are prepared and mixed with graphene.The phosphorus-doped silicon 50 cycle the capacity could still 1268 mAh/g after 50 cycles,which the capacity retain is also 46.7%.the phosphorus-doped silicon nanoparticles are mixed with graphene(P-Si-60@G),the first discharge specific capacity is 2313 mAh/g,after 95 cycle the capacity can still 866 mAh/g,capacity retention rate was 37.4%.(3)Porous silicon materials are prepared by chemical etching method,and the mechanism influence of pore-forming and carbon coating of silicon materials on the electrochemical properties is investigated.The first discharge specific capacity of the porous-Si and porous-Si@C materials is 3316 mAh/g,3072 mAh/g,after 100 cycle the capacity is still 714 mAh/g,778 mAh/g,the capacity retention rate is 21.5% and 25.3%.Because of the high specific surface area can improve the electron and ion transport capacity of the material..Further coating of carbon will detoriate the cell performance due to the presence of oxygen containing functional groups in the coating layer.