Preparation And Electrochemical Performance Of Silica-Based As Anode Material For Lithium Ion Batteries

With the popularity and application of portable electronic devices and new energy vehicles(NEVs)in daily life,traditional lithium-ion batteries with low energy density have been unable to satisfy the requirement for energy storage devices with high energy density.Correspondingly,the development of lithium-ion battery materials with high energy density,safety,economic and environmental protection has become an important work.As one of the key factors to improve the storage capacity of lithium-ions,anode material has become the focus of attention in the past decades.Silica with a theoretical specific capacity of 1965m Ah g^-1 is a strong contender as a potential replacement for graphite electrode in the next generation of lithium-ion battery anode material.It has been widely used in the glass industry and the electronics industry and is an ideal anode material for lithium-ion battery.However,Some problems with silica are not negligible when it is used as an anode material for lithium-ion batteries.Silica(SiO₂)has a very low conductivity as an oxide of silicon,which will lead to the formation of more irreversible substances when silica is combined with lithium ions,leading to the low initial coulomb efficiency of the battery system and further affecting the battery performance.At the same time,the volume expansion caused by the combination of silica and lithium ion is also not negligible.The volume expansion often makes the electrode material fall off from the collector,which leads to the increase of internal resistance and affects the cycle life of the battery.A large number of studies have shown that the composite and structure design of silica can effectively improve the battery life and the cycle stability of battery performance.Therefore,this article provides new strategies by Porous carbon(Pc)materials and metal Tin(Sn)to form SiO₂/Sn?SiO₂@Pc and SiO₂@Pc/Sn composite materials,which can improve the performance of the battery to storage Lithium ions.Specific research results are as follows:(1)SiO₂ and Sn with porous structure were fused at different proportions by simple ball milling and low temperature melting to produce SiO₂/Sn composite anode materials with different molar ratios.Compared with the different samples of SiO₂/Sn composites,mass ratio is Sn:SiO₂=1:10(SiO₂/Sn-10)has better cyclic stability,faster lithium-ion transport rate and high specific capacity and other electrochemical properties.The change rate of specific capacity of the battery system assembled at SiO₂/Sn-10 is 12%when it cycles to 200 cycles and the specific capacity reserve at 613 m Ah g^-1,the capacity retained up to 95.3%after the rate testing under different current densities,which indicates that the battery system has good capacity reversibility.Through the linear fitting of the relation between electrochemical impedance spectroscopy and different frequencies and the relation curve between CV of different scanning rates and peak current,it can be concluded that SiO₂/Sn-10 has a faster lithium-ion transport rate.The electrodes of SiO₂/Sn composite material after charging/discharging are measured by XPS and the samples after charging/discharging are qualitatively analyzed.The results show that the appropriate proportion of Sn can improve the conductivity of SiO₂ and make the composites have better cycle stability and capacity reversibility.(2)In order to investigate the effect of porous carbon material on the improvement of SiO₂ performance,SiO₂@Pc composite anode material was prepared by freeze-drying method.The results of electrochemical test show that Pc in a suitable proportion can greatly improve the cycle stability of SiO₂.The specific capacity of mass ratio is SiO₂:Pc=1:2(SiO₂@Pc-2)can reserve 446 m Ah g^-1 after 100 and the capacity retention rate is 93%after100 cycles.While the initial coulomb efficiency is raised up to 45%from the original value of 29.9%of the SiO₂ with Pc coating.The main factor is that the Pc can improve the electrical conductivity of SiO₂ and the porous structure in the SiO₂@Pc composite provide buffer space for the volume change of SiO₂ and improve the cycle stability of the composites.Through the linear fitting of the relation between electrochemical impedance spectroscopy and different frequencies and the relation curve between CV at different scanning rates and peak current,it can be concluded that SiO₂@Pc-2 has a faster lithium-ion transport rate,which indicates that the conductivity and cycling stability of SiO₂ can be improved after the compound of Pc and SiO₂ in appropriate proportion.(3)SiO₂@Pc with porous structure was prepared by freeze-drying method and then Sn and SiO₂@Pc were fused to produce SiO₂@Pc/Sn composite anode material.Electrochemical testing results show that the SiO₂@Pc/Sn composites have faster lithium-ion diffusion rate and higher specific capacity and the capacity remains at 463 m Ah g^-1 after 100 cycles,initial coulomb efficiency up to 51.1%.The fitting of electrochemical impedance under different frequency and different scan rate of CV,reveals that the SiO₂@Pc/Sn has faster lithium-ion transport rate,indicating that the Pc and Sn can improve the electrical conductivity of SiO₂and the volume expansion of Sn can be further restrained and accommodated by the SiO₂ and Pc.