Based On Graphene/Silicon Nano Particle Lithium-ion Battery Anode Materials Research

Silicon,as an anode material for lithium ion battery,has a very high theoretical specific capacity(?4200 mAh·g-1),it is considered as one of the most promising materials to replace the traditional graphite material(372 mAh·g-1).However,silicon exists huge volume expansion(>300%)during the process of charging and discharging,which results in the fast attenuation of specific capacity and limits its commercial application.Graphene,a kind of two dimensional materials,possesses many characteristics such as high specific area,excellent electrical conductivity and high mechanical strength.By compositing graphene with silicon,the electrochemical properties and stability of silicon can be improved.In this study,using graphene oxide(GO)as the precursor,graphene/silicon(G/Si)composites with different composition ratios were prepared.The effects of the composition,reduction temperature and polyvinyl alcohol have been investigated in terms of the morphology,structure,chemical composition and the electrochemical properties.The main research contents and results are as follows:(1)Detailed studies on the pretreatment of silicon and graphene/silicon components have been carried out.Using hydrofluoric acid to etch commercial silicon(100?120 nm)can effectively remove the silicon oxide.Although the silicon after pretreatment(P-Si)possesses a higher initial capacity,the cycling stability is relative poor.GO/P-Si nanocomposites were fabricated by solution mixing method.With the reduction of Silicon content,the specific capacity of the composites increased first then decreased.Besides,the cycling stability has been significantly improved.The results showed that the electrochemical performance of G/Si nanocomposites is the best when the ratio of(GO/P-Si)is 6:3.The specific capacity remained 866.2 mAh·g-1 after 100 cycles,indicating that the cycle stability has been improved.(2)The influence of heat treatment temperature on the GO/Si composites has been studied.The results showed that the conductivity of r-GO/Si composites increased with the increasing of temperature,as well as the cycle stability.However,when the temperature reached to 1050 ?,the chaos degree of graphene structure increased according to the ratio of D peak to G peak testing by Raman spectroscopy and the silicon nanoparticles agglomerated which was proved by TEM,leading to the lowest initial specific capacity.It is proved that the composites reduced under 700 ? possessed the best electrochemical performance.(3)The influence of polyvinyl alcohol(PVA)has also been discussed.Based on the GO/Si = 6:3 composites,Graphene oxide/silicon/polyvinyl alcohol(GO/Si/PVA)composites were successfully prepared.The addition of PVA can adjust the structure of composites.After thermal reduction,G/Si/PVA composites have excellent electrochemical properties.The electrochemical performance the stability reached the highest value when the composition ratio of the sample is GO/Si/PVA= 6:3:2.The specific capacity maintained 933.6 mAh·g-1 after 100 cycles and the capacity retention reach 82.8%.