Modification Research Of The Si-based Anode Material For Lithium-Ion Battery

Lithium ion batteries are widely used in portable electronic products because of their high energy density,high operating voltage,long cycle life and no pollution.But with the development of portable electronic products and the demand of lithium ion battery in aviation,military and automobile industry is increasingly strong,the capacity and energy density of the battery needs to be greatly improved.At present,the commercial lithium ion battery mainly uses the modified natural graphite and artificial graphite as the negative electrode material with excellent cycling performance.But because of its low theoretical capacity(Li C6 372 m Ah/g),there is an urgent hope for new type of negative for high capacity and long cycle life.Silicon is noticed due to its high theoretical capacity(4212m Ah/g).its voltage platform is slightly higher than graphite,in the charge to avoid the surface of the "lithium" phenomenon,the safety performance is better than the graphite cathode material.In addition,silicon is the second abundant element in the earth's crust,which makes up 25.7% of the total mass of the earth's crust.However,the Si based materials as anode materials for lithium ion batteries,the reversibility is not ideal.This is due to the Si intrinsic low conductivity and silicon-based materials in lithium ion insertion / removal process and huge volume change(800%-400%).Using the electrical conductivity better SFG-6 instead of graphite conductive carbon materials,The prepared Si O-C cathode material has good electrochemical performance(Electrochemical capacity 950 m Ah/g,the capacity hadn't obvious attenuation after cycle 50).At the same time,in order to solve the problem of low efficiency of Si O material for the first time,the oxygen atoms in Si O are transferred into inert by the method of active metal reduction and high temperature heating and it can effective alleviate the volume expansion of Si.Using the method of surface modification,adding a small amount of Li2 O and Al2O3 improve the surface stability of the material and the cycle performance.But the cycle efficiency of the first week is not obviously improved.In view of the above problems,the preparation of Si anode material,the improvement of electrochemical performance of Si O materials,the application of nano silicon based anode materials and the practical application of Si O-C composite materials were studied.The SEI formed on the surface of the silicon was more stable by adding a good film forming additive in the electrolyte CDK08.The electrochemical delithiation capacity exceed 950 m Ahg-1,and the coulomb efficiency of Si O-C material gradually increased to 99.8% which close to the level of carbon materials.A spray drying method was used to prepare the Si O-C particle size homogeneous stable precursor to form a silicon graphite carbon composite layered l silicon based anode material;Under the premise of keeping the original capacity and good cycling stability,preparation of the regiment concentration low,smaller particle size of the electrode material,the pre-lithium treatment and the first week of the irreversible capacity is significantly reduced.