Study On The Modification And Properties Of Silicon Negative Electrode Materials For Lithium Ion Batteries

As the negative electrode material of the lithium ion battery,silicon based materials have hight theoretical specific capacity(4200mAh.g^-1),about 10 times that of graphite negative electrode(372mAh.g^-1).However,with lithium ion repeatedly charging and discharging in silicon anode materials,the silicon material has a irreversible large volume expansion,the expansion rate is about carbon anode materials for lithium ion battery 300%.In order to solve this problem,in this paper,three kinds of silicon materials,including silicon,ferrosilicon and silicon dioxide,were modified,and compounded a certain amount of graphite.The lithium ion battery with high specific capacity and stable cycling performance was prepared.The phase and composition of the composites were characterized by scanning electron microscopy?SEM?,X ray diffractometer?XRD?and infrared spectroscopy.The electrochemical properties of the composites were tested by Wuhan blue electric test system and electrochemical workstation.The specific contents and conclusions are as follows:?1?The modification of silicon,Micrometer silicon?1?m?composite 40%artificial graphite was used as the negative active substance of lithium ion battery.The flake conductive graphite KS-6 was used as the conductive agent and the polyvinylidene ethylene PVDF was used as the binder.The mass ratio is the active substance:the conductive agent:binder =6:2:2.The composite material has good electrochemical cycling performance for lithium ion battery anode materials.The first lithium removal capacity was 3865.4mAh·g^-1,and the first coulomb efficiency was 72.5%.After 300 cycles,the reversible specific capacity was still 820mAh·g^-1.?2?The modification of ferrosilicon alloy,Using hydrochloric acid etching of Si-Fe?Si 40%?alloy powder prepared porous silicon material,and composite artificial graphite as anode material for lithium ion batteries.Through the study of the concentration of hydrochloric acid in Si-Fe alloy powder and the compound ratio with artificial graphite,it is concluded the best volume concentration of hydrochloric acid was 10%.The porous silicon material specific surface area was increased to 10.98m²·g^-1.The porous silicon material and artificial graphite mixed with the ratio of 1:2 for lithium ion batteries prepared anode active material.At 200mA g^-1 current density,the capacity of the first lithium removal ratio can reach 3214mAh g^-1,and the coulomb efficiency was 75.93%.After 100 cycles,there was still a reversible specific capacity of 845.3mAh·g^-1.It can be seen that the charge and discharge have a certain stability.?3?The modification of silica,Through high energy ball milling and high-temperature pyroly,prepared composite material SiO2/AG had excellent electrochemical performance.The electrochemical performance test showed that the prepared composite material,SiO2 composite materials containing 20%mass by the high temperature of 600? prepared electrode.In 200mA g^-1 charge discharge current density,the initial discharge capacity of 1763.6mAh g^-1,the coulombic efficiency was 58.98%,after 60 cycles,the discharge capacity still maintained in 1200mAh g^-1,showed a high charge discharge stability.Based on the above three kinds of silicon materials,we have found that the silicon material has poor conductivity and bonding.So no matter the silicon,or by hydrochloric acid etching into porous silicon or silicon oxide,all requires to compositea certain amount artificial graphite.In three kinds of silicon material,silicon high cost,especially the smaller the particle size of the more expensive;porous silicon etching silicon alloy powder,ferrosilicon powder although the price is low,but the preparation of porous silicon and the pore size distribution and poor controllability;silicon oxide has a wide source,low cost,preparation good controllability and other advantages,the prepared battery capacity,cycle life and stability also shows certain advantages.