The Synthesis And Properties Studies Of Porous Si-Based Anode Materials For Lithium-ion Battery

With the rapid economic development, energy and environmental problems have become more and more serious. The achieving of a green, low-carbon and environmental protection development has become an important direction of present research. As a good replace of traditional source such as oil and coal, Lithium-ion battery was widely used in portable electronic devices, new energy vehicles and other areas. It is urgent need to develop a higher energy density, longer life, lower cost of lithium-ion batteries. Silicon is considered the most promising anode material for lithium-ion batteries for it is highest theoretical lithium storage capacity of 4200 m Ah g^-1, lower off-lithium intercalation potential?<0.5V?, abundant reserves, etc.. However, silicon-based electrodes suffer from very poor cyclability due to loss of electronic contact between the active particles,resulting from the volume changes by 300% of Si upon insertion and extraction of lithium. For these reasons, the commercial use of silicon-based anode materials was severely hampered. The decrease of size to make nanometer silicon particles, combine with cushioning material to prepare composite materials and design porous structure to buffer the volume change of Si were the main solutions to enhance the cycle life of Si-based anodes. The porous Si-based composites can buffer the volume change of the silicon effectively and provide a large number of channels for the transmission of ions. Preparing of porous Si-based composites was considered as one of most useful way to improve the electrochemical performance of Si-based anode. However, the complexity preparing process, high cost, limited cycle life and other issues have not been solved during the preparation. In order to solve the above problems, three ways were introduced to improve the electrochemical properties of porous silicon anode material by the present paper. The main work is as follows:?1? Design of hollow porous Si/C composite. A carbon layer was coated on the surface of porous Si/C material to block up the surface of hole by CVD method. The porous Si/C material was obtained by etching silicon dioxide?SiO₂? from Si/SiO₂/C composites with use of HF. On the one hand, it can reduce the absorption of large amount of solvent and the binder in the mixing process. On the other hand, reducing the amount of binder and conductive agent is equal to improve ratio of the active material, which helps to improve the volume capacity of the battery. The binding force between composite and collector was enhanced and no obvious decline was seen after 100 cycles.?2? A Si/C composite is synthesized by Spray drying,carbonization and washing with Na Cl as pore-forming agent. Compared with using HF or HCl to move away SiO₂ or CaCO₃, this method is more environmentally, simple and is not critical to the equipment. The as-prepared Si/C composites lithium ion battery anode displays excellent cycle performance of 83% capacity retention after 100 cycles at a current density of 0.4A g^-1 and good rate performance.?3? A novel Si/Ni/CNTs composite is designed and fabricated by in-situ growing CNTs on the Si nanoparticles with co-precipitated Ni nanoparticles as catalyst. It is found the as-grown CNTs have a much stronger bonding force by embedding the CNTs into the composite with the formation of a buffering interface. Thus, the structural stability would be improved greatly and the cycle life would be enhanced significantly accordingly. The corresponding discharge capacity could be remained at around 550 m A h g^-1 with capacity retention of 84% after 300 cycles, while the high rate capability was also achieved with a discharge capacity of 420 m A h g^-1 at 10 C.