| Si is the most promising cathode material for lithium-ion battery,because Si has the highest specific capacity among all the elements using as the cathode material of lithium-ion battery.The specific capacity of Si is about ten times than that of C,which is used in current commercial lithium ion batteries.In this way,the energy density of the cathode materials will be greatly improved.Moreover,the safety performance of silicon is better.The voltage platform of Si is slightly higher than that of graphite,which would increase the power density and prevent the precipitation of Li on the surface while charging.In addition,Si is abundant in the crust and that would make it cheap,help to reduce the cost and promote the commercialization of lithium-ion battery.However,Si cannot serve alone.This is because the cycling performance of Si is rarely poor.In the process of electrochemical storage,the volume expansion of the material will be more than 300%.The mechanical stress caused by this massive volume effect will continuously destroy the solid electrolyte interphase(SEI)formed on the surface of the electrode,thus reducing the transmission efficiency of Li~+and affecting the performance of the battery.At the same time,Si itself will be pulverized and gradually separated from the fluid collector until the contact is lost,resulting in a decrease in charge and discharge efficiency and a rapid decrease in the cycling performance.What's more important,as a typical semiconductor material,the resistivity of Si is extremely high.The conductive ability of the electrode must be improved in the process of application,and this will affect the electrochemical properties of the electrode in many other ways.In this paper,a series of Fe-Si amorphous films were prepared by magnetron sputtering,and the effect of Fe content on the properties of the thin films was studied after selecting the suitable film thickness.As the properties of amorphous materials are closely related to their local structure,it is also the focus of this paper to see whether the local structure of the film will affect the electrochemical performance when they are used as electrode materials.The physical characterization and analysis of the films were carried out by X ray diffraction,transmission electron microscopy,UV-visible-near infrared spectrophotometer,et al.The electrochemical test of the materials was carried out by constant current charge-discharge and CV test,et al.The physical characterization results of the material show that the film's surface is smooth with good density.Whats'more,two different semiconductor properties (Direct band-gap and indirect bandgap)are present separately with the change of composition,indicated that the Fe-Si films have different local structures.The Fe-Si amorphous films with a thickness of about 250~350nm have better cycling stability.The specific capacity of the amorphous Fe-Si film cathode maintained 621mAh/g after 100 cycles,and the coulomb efficiency of the charge and discharge process is nearly 100%.However,there are obvious differences in the performance of the film electrode with different composition interval,which is mainly due to the difference of the film local structure of different components.C is a kind of lithium ion battery anode material with excellent cycling performance.On the basis of the previous article,a small amount of Fe-Si-C amorphous thin films have been prepared by the same method.It can be seen from the results of X ray diffraction that the amorphous Fe-Si-C films have been successfully prepared.In addition,the results of constant current charge discharge test show that with the increase of Fe and C elements in the film,the cycle performance of the corresponding battery has been improved,but the specific capacity level is slightly decreased. |
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