The Preparation And Battery Characteristics Research Of Silicon Anode Materials

Due to the outstanding characteristics,lithium-ion battery has become the leading of the new energy market.However,with the high-speed development of science and technology,the capacity(372 mAhg^-1)of the graphite material of the commonly commercial anode in lithium ion battery gradually cannot meet the needs in various fields.Therefore,in the recent years,the research and development of new anode materials has become the focus in the field of lithium ion batteries.In all candidate materials,silicon material becomes the focus due to the highest specific capacity.In addition,the advantages of the low potential and rich raw materials are the significant factors that the silicon material become the most potential candidate.However,silicon particles exhibit serious volume change during the repeatedly cycles,which easily causes the crack and crush of silicon particles,and loss the electrical contact between Si particles and conductive carbon,causing the serious capacity fade and poor cycle stability.In addition,the electrical conductivity of the silicon material is very poor.Therefore,how to ensure high capacity,improve the cycle stability performance and increase cycle life are the research focus.In recent years,many studies find that nano-materials can improve the diffusion rate of Li+ in the anode,reduce the volume change of silicon particles,and improve the various performances of materials.However,these materials run into new problems of electrochemical agglomeration and surface side reactions,which limit their expected advantages.Based on these,we prepared silicon composite materials with nano-silicon as raw materials to improve the various electrochemical performances of the lithium ion battery.At the same time,we developed a novel polymer binder for Si anode materials to improve the all electrochemical performances of the lithium ion battery.The main content of this thesis:?1?we successfully synthesize a yolk-shell structured Si-PPy composite by an in situ chemical polymerization approach.In the process of synthesis,Polyvinylpyrrolidone is used as the combination of the polypyrrole and silicon,and then enhance stability of composite electrode.Compared with bare Si,the Si-PPy composite exhibits outstanding electrochemical performances,including the capacity of 1400 mAhg^-1 after 100 cycles,which is 4 times higher than bare Si in the same conditions and superior rate capability.This improvement of electrochemical performance could be attributed to the stable PPy shell,which not only can effectively relieve the massive volume change of silicon particles,but also can increase the conductivity of silicon.?2?we successfully develop a novel,flexible PVA–PEI polymer binder via in situ thermal cross-linking.The reaction of the hydroxyl and amide group end up with the formation of the flexible cross-linked network structure.The experiment show that silicon anode with PVA-PEI binder has high specific capacity of 1063.1 mAhg^-1 after 300 cycles and high initial coulombic efficiency of 83.8% at the current density of 1 Ag^-1.Furthermore,silicon anode with PVA-PEI binder still has excellent specific capacity of 1590 mAhg^-1,when the current density increases to 10 Ag^-1.These superior cycle stability and rate performance of the silicon anode with PVA-PEI binder are attributed to the strong adhesion which can assist in forming stable electrode structure,and the crosslinking structure of binder which can increase effectively alleviate the severe volume change of silicon electrodes during the lithiation and delithiation process.