Study On The Preparation And Performance Of Silicon-based Lithium-ion Battery Anode Materials

The utilization of renewable energy requires stable energy storage devices.Lithium ion batteries have been applied to many fields such as new energy vehicles,wind and sun power generation energy storage,signal base stations and small mobile devices due to their advantages of long cycle life,light weight,no memory effect and low self-discharge rate.With the acceleration of the social development,higher and higher energy density of lithium-ion battery is required.In the future,commercialized graphite anodes cannot meet the requirements of high energy density.High-capacity anode materials have been rapidly developed.Silicon-based anode materials have high theoretical specific capacity and a promising prospects.However,the inherent poor cycle performance and poor rate performance have seriously hindered their further development.Therefore,it is of great practical significance to study how to solve the shortcomings of silicon-based materials,such as poor cycle performance and poor rate performance.In this thesis,on the basis of analyzing the failure mechanism of silicon-based anode materials,we designed the Si-FPC-SC（Flour-derived porous carbon,FPC,Sucrose-derived carbon,SC）and Si-MWCNTs-PVPC-FPC-SC to improve the cycle performance and rate performance of silicon-based anode materials significantly.The main findings are summarized as follows:1.We designed a kind of porous carbon derived from wheat flour by a shape-preserving carbonization process,which can meet the requirements for encapsulating high-capacity active substances.The single variable method was adopted to adjust the carbonization temperature and carbon/KOH ratio to explore the optimal experiment conditions:the carbonization temperature is 750℃and the carbon/KOH ratio is 1:2.2.Different contents of Nano Si was encapsulateed into FPC through electrostatic adsorption.Due to the conductive framework of porous carbon,its buffering effect on the volume expansion of silicon and its good dispersion effect on Si nanoparticles,the cycle performance of silicon-based material was improved.With the increase of silicon content,the capacity of Si/C composite materials had steadily increased.When the silicon content reached 40%,the porous carbon structure was destroyed.After the structure of Si-FPC-SC was optimized,we obtained30%-Si-FPC-SC.After 100 cycles at a current density of 0.1 A g^-1,it is reversible capacity was 937 m Ah g^-1.3.The freeze-drying method was used to add the multi-walled carbon nanotubes into the porous carbon structure,which solved the problem of highly dispersed carbon nanotubes and nano-silicon’s reagglomeration during the air drying process.The prepared Si-MWCNTs-FPC-SC’s rate performance was improved greatly.After cycled at different current density,the reversible capacity reached 441.4 m Ah g^-1 at 5A g^-1,which is 33%of it’s reversible capacity cycled at 0.1A g^-1.After 500 cycles at the high current density of 1 A g^-1,the specific capacity was still 306 m Ah g^-1.