Study On The Properties Of Silicon Based Anode Materials For Lithium Ion Batteries

Theoretical specific capacity of silicon is as high as 4200 mAh/g,which is expected to be one of the new generation of high-capacity negative materials.However,in the process of intercalation and de-lithium,it can cause silicon particle volume expansion and electrode structure collapse,resulting in weakening silicon and current collector conductivity.It will affect the electrochemical performance of the battery.In order to improve this problem,this paper studied the effects of sodium alginate on different silicon-based composite materials(silicon anode material,silicon/graphene anode material,silicon/iron anode material),and analyzed rheological roperties of negative electrode material and sodium alginate composite slurry.Meanwhile the electrochemical properties were investigated.This study tries to improve the electrode structure,exploring lithium-ion battery with high specific capacity and electrode cycle stability.The main work and results of this paper are as follows:(1)The experiment prepared three kinds of lithium ion battery with different sodium alginate binder conten,and testing and comparing slurry rheological and thixotropy.The suitable content of sodium alginate binder was screened at 20%.At this content the negative electrode slurry particles could form a uniform,stable dispersion structure.The study also tested the electrochemical properties of the system.The results showed that the first discharge specific capacity was 2200 mAh/g and the Coulombic efficiency was 87% as the mass ratio of the anode material(nano silicon),the conductive agent and the binder was 6:2:2.But after 50 cycles of circulation,the discharge capacity was less than 800mAh/g.In the process of lithium and de-lithium of lithium-ion batteries,silicon will undergo volume expansion,resulting silicon material powdering,peeling,loss of electrical contact.So the capacity of lithium-ion battery decaies quickly,and the cycle stability is poor.(2)It can be achieved by improving the electrical contact between the silicon particles and the current collector in order to improve the cyclic stability of the lithium ion battery on silicon negative electrode.In this paper,a graphite/graphene anode material was prepared by introducing graphene material with excellent electrical conductivity in the silicon anode.The rheological and thixotropy of silicon/graphene negative slurry of three different sodium alginate binders were tested.The choosed best sodium alginate binder content was still at 20%.On the basis of the mass ratio of the anode material,the conductive agent and the binder at 6:2:2.The electrochemical properties of three kinds of silicon/graphene lithium ion batteries with 10%,20% and 30% contents were tested.The results showed that with the graphene content decreaseing,the specific capacity increased,and the internal resistance decrease.After cycling 50 times,the 10% content of silicon/graphene lithium-ion battery,discharge capacity was more than 1800mAh/g.After 100 times of circulation,the specific capacity of the discharge was about 1650 mAh/g,so the appropriate amount of graphene was beneficial to improve the cycling of lithium ions.(3)In order to improve the cycling stability of the silicon-based lithium ion battery,it is possible to prepare the porous silicon/metal composite material for the expansion space of the silicon volume.In this paper,microporous silicon/ferroalloy anode materials were prepared by acidizing ferrosilicon alloy.In this paper,microporous silicon / ferroalloy anode materials were prepared by acidizing ferrosilicon alloy.The rheological and thixotropy of the microporous silicon/ ron negative paste based on the sodium alginate binder was tested,and the suitable content of sodium alginate binder was determined to be 20%.The first discharge capacity was as high as 2600 mAh/g,and the charge/discharge capacity is about 1250 mAh/g after 50 cycles when the mass ratio of the negative electrode material(microporous silicon/iron),conductive agent and binder was 6: 2: 2.The specific capacity was decreased,but the porous structure effectively enhances the stability of the cycle performance.