Structural Optimization And Electrochemical Properties Of Anode Materials For High Specific Capacity Lithium Ion Batteries

Lithium ion batteries(LIBs)with light weight,high energy density,small volume,long life cycle and environmental friendly etc are widely used in today’s new energy field,but the current commercial applications of graphene lithium ion batteries because of low capacity(372 m Ah/g),making it unable to meet the needs of people at this stage,the silicon as electrode material,has very high theoretical capacity(4200m Ah/g)and become one of research hot spots.However,in the process of lithium ion stripping/embedding,the bulk expansion effect will lead to the pulverization of electrode material and then the fall off from the copper foil,which greatly reduces its electrochemical performance.By changing the morphology,structure and use carbide Yeast Powder(Carbonized Yeast Powder,CYP),reduction of Graphene Oxide(Reduced Graphene Oxide,rGO)and Carbon Nanofiber/Nanoparticles(Carbon Nanofibers/Nanoparticles)composite with Si,anode of lithium storage material was prepared with high specific capacity.Carbon coated silica nanoparticles(SCNPs)were synthesized by hydrothermal method,and then SCNPs/rGO were obtained by secondary coating of SCNPs using reduced graphene oxide.The SCNPs/rGO composite material is used as the negative electrode material of lithium ion battery(LIBs)and the battery assembly test is carried out.After cycling 150 times at the current density of 150 m A/g,it still has a reversible specific capacity of 977.5m Ah/g.Meanwhile,in the multiplication performance test,it has a reversible specific capacity of 1338.1m Ah/g at the current density of 200 m A/g.Compared with SCNPs circulation after the reversible specific capacity and rate performance tests,compound the reduction of graphene oxide silicon carbon nanomaterial has more excellent performance,the two materials for Electrochemical Impedance spectrum(Electrochemical Impedance Spectroscopy,EIS)analysis,under the same testing cycle,SCNPs/rGO Nyquist half arc and charge transfer Impedance is more small with smaller than SCNPs,the conductivity of SCNPs/rGO was an order of magnitude higher than that of SCNPs after the cycle test,This indicates that the addition of rGO improves the material conductivity and plays a positive role in the diffusion of lithium ions,so the composite SCNPs/rGO is more suitable to be used as a negative lithium storage material for lithium ion batteries with high specific capacity.Nanoscale Silicon carbon nanofibers(SCNFs)were prepared by electrostatic spinning method,and then SCNFs/CYP was synthesized by hydrothermal method combined with carbonized yeast powder.By increasing the specific surface area and utilizing the porous structure of the biomass carbon material,the electrical contact points and electrolyte penetration are increased more effectively.The specific capacity is 2488.4,2116.1,2082.2,1738.1,1482.2 and 2416.7 m Ah/g when the charge-discharge ratio is 0.1c,0.5C,2C,5C and 0.1C,respectively.The excellent electrochemical performance was attributed to the inhibitory effect of the porous structure of carbonized yeast powder and the carbon nanofiber structure on the volume expansion effect and the hindrance to the agglomeration of silicon particles.In terms of electrical conductivity,as the number of cycles increases,the electrical conductivity of SCNFs/CYP becomes higher and higher,and the electrochemical stability also improves.Integrated these two modification methods,on the one hand,can have obvious inhibitory effect of volume expansion effect,reduce the aggregation of active material,reduce the internal resistance of battery,on the other hand enhance the electrical conductivity of electrode material to improve the cycle stability of the battery,for battery energy storage behavior in the electrochemical reaction process.