Electrochemical Performances Of SiO₂ As Anode Materials For Lithium-ion Batteries

In this work,SiO₂ was selected as the subject for electrochemical lithium storage on the basis of a review of progress in SiO_x anode materials.The effect of ball milling treatment,binders,calcining temperature and carbon composite on the morphology,microstructure and electrochemical properties of SiO₂ was systematically studied by a series of XRD,SEM and electrochemical property measurements.The relationship between the composition,morphology,microstructure and electrochemical properties of SiO₂ anode material was elucidated in this work.This study provides the experimental and theoretical guide for further designing and developinghigh-performance SiO₂ anode for Li-ion batteries.In this paper,commercial available SiO₂ was used as raw materials to fabricate SiO₂ anode material by mechanical milling.For the SiO₂ anode material,the reversible lithium storage capacity gradually increased with the milling time.The sample milled for 72h showed the best overall electrochemical properties.At the current density of 100 mA g^-1,the initial discharge capacity was 1435.7 mAh g^-1 and the initial coulombic efficiency was 54.5%.After 100 cycles,SiO₂ milled for 72h could remain 574.3 mAh g^-1,which was greater than 188.9 mAh g^-1 of the pristine SiO₂.At thehigh current density of 400 mA g^-1,the reversible capacity of SiO₂ was still over 480 mAh g^-1.The XRD results showed that with the increase of milling time,the crystallization performance of SiO₂ degraded gradually.After 72h milling,the crystalline SiO₂ was converted to an amorphous one.Further SEM observation showed that with the increase of milling time,the particle size of SiO₂ became smaller and its particle distribution was more uniform,resulting in the improved electrochemical activity and the increased lithium-ion diffusion.This is the reason for the lithium storage properties of SiO₂ affected by the mechanical milling.SiO₂ after 24h and 72h milling were selected to study the influence of binders on the electrochemical properties.For the material after milling 24h,the PVDF-electrode retained only 22% capacity after 100 cycles,while the CMC-electrode was 34%.For the material after milling 72h,the PVDF-electrode retained only 16.5% capacity after 100 cycles,while the CMC-electrode was up to 40%.The explaination of the difference might be the CMC binderhad greater adhesion strength and larger breakage elongation,it could stick to the particles and current collector to withstand a greater stress before de-bonding and to tolerate a greater extent of volume expansion with reversibility.The effects of calcination temperatures on the electrochemical properties of SiO₂ after milling 72h were studied.With the gradual increase of the calcination temperature,the reversible capacity of the material gradually decreased.The reversible capacity of sample calcined at 1000 °C was similar to the pristine SiO₂.The XRD results showed that samples calcined at 400 °C and 600 °C still revealed an amorphous nature.When the calcination temperature reached to 100 °C,the characteristic peaks corresponding to crystalline SiO₂ appeared,revealing a crystal nature.The SEM results showed that the particle size of samples calcined at 400 °C and 600 °C changed little.When the calcination temperature increased to 800 °C,particles began to grow,and bonding phenomenon could be observed.When the temperature reached to 1000 °C,the particle size of the material was significantly larger with serious agglomeration.Citric acid was used as carbon source to fabricate SiO₂/C composites by sol-gel method.The effect of calcination temperatures on the morphology and microstructure of SiO₂/C composites was studied.The relationship between the weight ratio of carbon and electrochemical properties of SiO₂/C was also revealed.It was found that the SiO₂/C composite with 13.1 wt% of carbon exhibited good electrochemical lithium storage properties.The initial efficiency was 67.9%,the discharge capacity reached to 624.9 mAh g^-1 and the capacity retention was 70.8% after 100 cycles.The SEM results showed that SiO₂ particals were uniformly wrapped by carbon networks,leading to effective improvement of the electrical contact of SiO₂ anode material.