Structural Design And Initial Coulombic Efficiency Of Silicon-based Anode Materials For Lithium-ion Batteries

Energy crisis and environmental issues promote the development and utilization of new energy.Energy storage technology is one of the key technologies for wide application of new energy.Moreover,with the development of information technology and mobile Internet,portable and intelligent electronic/electric devices,the demand for high-performance batteries becomes higher and higher.The development of advanced high-specific-energy batteries and high-specific-capacity cathode and anode materials is the key to improving the energy density of batteries.Silicon?Si?has the advantages of high theoretical specific capacity(⁴200 mAh g^-1),suitable working potential?⁰.4 V vs.Li/Li⁺?,abundant reserves,low cost and environmental benignity.It is one of the most promising anode materials for lithium-ion batteries?LIBs?.However,problems such as poor cycling performance and low initial Coulombic efficiency?ICE?of Si anodes hinder its commercial application.These problems result from the huge volume and structure changes of Si during charge and discharge process.Therefore,it is very important to study the influence of material structures on the electrochemical performance and the influence factors of ICE for designing high-performance Si anodes.In the first part of this thesis,one-dimensional?1D?Si nanowires?Si NWs?were prepared,and the lithium-storage properties of the Si NWs were studied.The influence of material structures on the electrochemical performance was investigated.In the metal-assisted chemical etching?MACE?method,the length of Si NWs mainly depends on the etching time and the concentration of AgNO₃ and HF of the etching solution.The doping degree of Si wafer has an effect on the surface micro-morphology of Si NWs.The Si NWs with porous structures were prepared by heavily-doped Si wafers.Compared with non-porous Si NWs,the porous Si NWs have better cycling and rate performance than non-porous ones.The improved cycling performance is due to its porous structure,which is beneficial to alleviating the volume change of Si.In the second part,the influence factors of the ICE,prelithiation and full-cell application of Si anodes are studied.It is found that the size of Si,carbon content,binder and depth of discharge?DOD?have significant effects on the ICE of Si anodes.According to the research results,the concept of“intrinsic ICE”was proposed.The ICE of Si anodes can be increased to 100%through proper prelithiation treatment.The prelithiation treatment of Si anodes can not only improve the ICE of full cells significantly,but also improve theirs cycling performance.In this thesis,we have got some conclusions on the influence of the structure of Si material on the electrochemical performance,the initial irreversible capacity loss?ICL?,the influence factors and improvement of the ICE of Si anodes,the principle of lithium storage and failure mechanism of Si anodes.The research results are of great significance for the development of high-specific-capacity and high-ICE battery materials.