Study On The Silicon Cathode Materials And Electrochemical Performance Of High Capacity Lithium Ion Battery

Silicon materials are the most attractive candidates for the next generation of anode active materials of lithium ion battery(LIB),for the advantages of high theoretical specific capacity(4200mAh/g),low intercalation potential and abundant resources.But the drawbacks of low conductivity and the poor cycling performance induced by 4times volume expansion limits the commercial applications of Si materials in LIB.In this paper,Si nanoparticle of 100 nm was used as the silicon source,doping with artificial graphite(G)or multiwalled carbon nanotubes,CNT conductive paper was used as current collector instead of copper foil,and prelithiated methods to improve the performance of silicon LIB.The main research results are as follows:Si has the feature of high theoretical specific capacity but bad cycling and conductivity,while G has the property of good cycling and conductivity but low theoretical specific capacity.Thus,the composite of nano Si and G were coated on copper foil to make an anode electrode.It was found that the space between G will provide a buffer function for the volume expansion of Si.And the Si-G composite electrode displayed high specific capacity in the low current density.But the capacity dropped quickly in the large current density.CNT paper which was combined by paper fiber and MWCNTs was used in lithium ion battery to replace the copper foil current collector,to load the composite material of MWCNTs-nano Si.CNT paper showed serious characters such as good conductivity,low area density,large contact area and strong absorbency.The silicon LIB with CNT paper showed high specific capacity of 1000 mAh/g and 500mAh/g in the current density of 80mA/g and 1000mA/g.What deserve attention especially is that compared with copper foil,the electrochemical impedance spectroscopy(EIS)of LIB with CNT paper decreased instead of increase after cycling.The CNT paper used as current collector has overcome the volume expansion effectively.The method of prelithiation with stable metal lithium powder(SMLP)has been chosen to reduce the big irreversible capacity of silicon LIB with CNT paper?The SEI membrane was formed spontaneously in the standing process of prelithiated battery.And the SEI membrane was compacter and stabler because of the slowly spontaneously formation.Thus it not only reduce the big irreversible capacity resultfully,but also improve the reversible capacity.