Preparation And Electrochemical Properties Of Si-based Anode Materials For Lithium-ion Batteries

Recently,the application of Li-ion batteries extends from 3C products to other high energy consumption areas such as electric vehicles and smart grids.The demands for more safety,higher energy density and longer cycle life have become urgent.However,commercial graphite anode hardly satisfy the requirements of high energy and power densities for the above-mentioned technological applications because of its low theoretical capacity(372 mA h g-1).Si has the potential to replace graphite due to its ultrahigh theoretical capacity of 3579 mA h g-1 based on the formation Li3.25Si alloy at room temperature,relatively low lithiation voltage,and abundance in nature.Unfortunately,the large volume change of Si active particles during charging/discharging process will generate internal stress,leading to the pulverization of electrode materials and the formation of unstable solid electrolyte interphase(SEI)layer and finally low coulombic efficiency and rapid capacity fading.Additionally,the poor electronic conductivity restricts the electrochemical reaction kinetics and rate performance of Si anode greatly.In this thesis,the conductive PANi is synthesized and used both as binder and conductive additive for commercial Si anode material to construct Si@SiOx/PANi integrated electrode.After that,Si@SiOx/PANi was carbonized to synthesize Si@SiOx@C.During the carbonization process,FeP is introduced into the obtained C layer.By means of the different lithiation potentials between Si and FeP,the formed Fe nanocrystals due to the reduction of FeP after lithiation can alleviate the volume change of Si and benefit to enhance the overall electronic conductivity of hybrid anode,finally leading to the obviously strengthened specific capacity and cycling stability.The main research works are as follows:Firstly,a three-dimensional(3D)conductive polyaniline(PANi)hydrogel is synthesized through in-situ polymerization and used both as binder and conductive additive for commercial Si nanoparticles to improve their electrochemical properties.The electrochemical performance of Si@SiOx/PANi electrode is researched in detail.In addition,the influence of different content of PANi on lithium storage properties has also been researched in detail.When Si mass percent is 90.6%,the designed Si@SiOx/PANi-100 electrode shows a reversible capacity of about 1137 mA h g-1 after 500 cycles with a very low capacity decay of 0.072%per cycle at 1 A g-1Secondly,on the basic of conductive PANi,Si@SiOx@C is synthesized through carbonization of Si@SiOx/PANi and FeP is introduced during the carbonization process.The Si@SiOx@C/FeP electrode shows a reversible capacity of about 1078 mA h g-1 after 400 cycles with a very low capacity decay of 0.027%per cycle at 0.5 A g-1 and of about 754.6 mA h g-1 after 400 cycles with a very low capacity decay of 0.048%per cycle at 1.0 A g-1.The influence of the FeP in Si@SiOx@C/FeP on the electrochemical properties is investigated in detail.