High-rate SiO₂/C Composites As Anode Material For Lithium-ion Batteries And Their Energy Storage Performances

To satisfy the requirements of new energy storage and electric vehicles,lithium-ion batteries with higher power density is demanded.SiO_2,which possesses high lithium storage capacity as well as less volume change than Si,is considered as a promising alternative anode to Si-based material.However,negligible electrochemical conductivity of bulk-SiO₂ limits its applications as anode for lithium ion batteries?LIBs?to great extent.Carbon coating of nano-SiO₂ is thought to be an effective strategy to improve the electronic conductivity.In this paper,two kinds of SiO₂/C composites with different morphologies have been synthesized in different reaction systems.SiO₂/C composite with irregular granular was synthesized in alkaline aqueous solution via a solvent evaporation method and subsequent heat treatment,by using amphiphilic carbonaceous material?ACM?as carbon precursor and tetraethyl orthosilicate?TEOS?as SiO₂ precursor.In the present of ACM,the diameters of generated SiO₂ nanospheres reduced from 500 nm to 340 nm,and the surfaces of SiO₂were coated by lamellar stacking carbon layers derived from ACM.When evaluated as anode materials for lithium ion batteries,the SiO₂/C composite exhibits a reversible capacitance of 440 mAh/g after 400 cycles even at a current density as large as 1 A/g.A series of SiO₂/C spherical composite with core-shell structure containing different content of SiO₂ nanoparticles were prepared in the limited domain system formed by hydrogen bonding between ACM-PEG400-NH₃·H₂O mixture,by using tetraethyl orthosilicate?TEOS?as SiO₂ precursor.The results of morphology analysis show that the SiO₂/C composite prepared by limited domain system has good sphericity and particle size.The diameters of the spherical composite is in the range of100¹50 nm,and the size of SiO₂ in composite is about 100¹30 nm.It is found that the SiO₂/C composite which containing 57.9 wt%SiO₂ is superior to other samples in electrochemical properties,which retains a large capacity of 483 mAh/g after 400cycles at a current density of 1 A/g,showing a better rate capability and cycling stability.The reaction mechanism of SiO₂/C composites in charge/discharge processes was carried out by XPS.By analysis the O 1s binding energy in the discharge/charge processes,it demonstrated that reactions between the SiO₂/C composite and Li-ion includes not only irreversible reaction which formed Li₂O and Li₄SiO₄,but also reversible reaction which formed Li₂Si₂O₅.