| Silicon（Si）is considered to be one of the most promising anode materials to replace carbon anode for lithium ion battery.However,there is a long-existing severe drawback,that is,a huge volume change during battery cycling,which would lead to fast capacity decays and even electrical contact failue of the electrode.Previous researches demonstrated the"yolk-shell"structure as an ideal structure to restrict the volume effect of silicon anode.The"yolk-shell"structure is generally prepared by chemical coating and etching.It is difficult to control the thickness and uniformity of the shell.Therefore,it is urgent to find a more sustainable method that can be easily operated and costs lowly.At the same time,the"yolk-shell"structure prepared by chemical etching method usually has a single-point contact between the core and the shell,and the contact is of weak van der Waals force,which is not conducive to the transport of lithium ions.On the other hand,carbon anode materials play an indispensable role in the development of lithium-ion batteries and are widely used in commercial lithium ions battery presently.However,the lithation potential of carbon materials is below 0.5 V,which is lower than the electrochemical stability window of the electrolyte.The solid electrolyte interface（SEI）can restrict the further decomposition of the electrolyte,which is beneficial to the stability of the battery.However,the formation of the SEI can cause irreversible loss of active lithium ions.The pre-construction of artificial SEI on the surface of the anode material would an effective strategy to solve the problem,considering it can isolate the direct contact between the electrolyte and the electrode,thereby reduce the irreversible decomposition of the electrolyte.However,the thickness of the coating layer is not easy to control,which will affect the transport of lithium ions.Moreover,the coating layer is generally made of insulating material,which would deteriorate the capacity of the electrode.To solve the above problems,in this thesis,we conducted the following researches:（1）By taking the advantage of the Kirkendall effect,multi-Si-void@SiO2 was prepared by one-step thermal oxidation of Si and the electrochemical performance was evaluated.The results show that in this structure,Si O2 shell as a protective layer can effectively prevent the contact of Si core with the electrolyte,and the multi-point contact between the shell and the core is beneficial to the transportation of lithium ions.At the same time,the Si O2 shell can provide a considerable capacity during the battery cycling.The prepared electrode can output a capacity of 1400 mAh g-1at the 1.2 A g-1.（2）Through a physical vapor deposition（PVD）,Cu/CuO/Cu2O was introduced into the carbon electrode surface to construct artificial SEI.It was found that the artificial SEI can effectively inhibit the formation of natural SEI.At the same time,as compared with the chemical-coating-modified electrode,the electrode prepared by PVD method can be continually activated accompanying certain structural changes.The artificial coating appeared hightly conducive to the transport of lithium ions.The initial coulomb efficiency is increased by about 20%,and the capacity is increased by nearly two times. |
