Synthesis And Properties Of Nano-structured Silicon-based Lithium-ion Battery Anode Material

The lithium-ion secondary battery has become the 21st century great potential for the development of new chemical power. At present, the most widely used lithium-ion battery anode material is a carbon material (graphite).Carbon material is a rich source of inexpensive, but lower theoretical capacity (372 mAh/g) and low potential (cause this material easy analysis of lithium surface, unable to meet the requirements of rapid charge and discharge) is difficult to meet the requirements of today require high power output and power battery fast charging. How to create a large-capacity, long-life, low-cost, low energy consumption, high output power, fast charge, safe, environmentally friendly secondary battery, battery research and development efforts in the direction.Silicon-based materials due to its high theoretical lithium storage capacity (4200 mAh/g,Li4.4Si) has great potential. However, silicon-based materials in lithium intercalation, lithium-off process, the introduction of the huge volume of deformation (> 300%), leading to electrode breakage and destruction of the conductive network, and greatly limits the cycling performance of the silicon-based material.For lithium-ion batteries, lithium properties of nanostructures improve material for many advantages. Since the nano-material has a very high specific surface area, increasing the contact of the electrode with the electrolyte, and having a high surface activity; nano-scale materials, lithium-ion in which the embedding depth is shallow, the diffusion path is short, there is conducive to a lithium-ion the fast deintercalation, have good dynamic properties of nanostructures can greatly improve the transmission capacity of the lithium-ions. In addition, the voids of the nanostructure can accommodate the volume expansion of the electrode material in the charging and discharging process, to prevent electrode fragmentation chalking. Graphene as a lithium-ion battery electrode material of the carrier, on the one hand can improve the material’s surface area, increasing the contact area of the electrode material with an electrolyte, on the other hand, due to the high flexibility of the graphene, can effectively prevent the active material the charging and discharging volume expansion stress is generated so that the electrode fragmentation.The most important point is that the highly conductive graphene effectively improve the performance of electronic conduction capability of the active substance.This work is committed to silicon-based nanostructures low-cost, high-yield preparation,Silicon-based materials of graphene-coated, and in the lithium-ion battery. Specific research work are as follows:The organic combination of magnesium thermal reduction technology, SiO2 microspheres preparation technology, the development of the porous Si microsphere preparation method. Si microspheres good contact between the porous material prepared by this method, the porous Si microspheres containing a large number of disordered pore is conducive to the infiltration of the electrolyte and the stress release. Stable mechanical frame connector porous Si microspheres, its charging and discharging the volume of deformation in the process to provide a buffer layer, electrochemical tests show that the microsphere material of the porous Si with respect to the graphite material having twice the capacity to enhance the structure effectively improve the the cycling performance of the silicon-based lithium-ion battery.Magnesium thermal reduction method to restore the SBA-15, three-dimensional mesoporous silicon particles, which preserves the original form of silica SBA-15. This optimization nanostructures uniform distribution of well dispersed mesoporous structure provides sufficient clearance to effectively adapt to the change in volume of the silicon as a buffer, thereby improving the cycle performance of the battery.The capacity after 50 cycles at 1600 mAh/g, capacity approximately commercialization five times the capacity of graphite (372 mAh/g), having a good cycle characteristic. And its reaction, a large number of cheap, non-toxic raw materials, large-scale commercial applications.Introducing silicon nanoparticles coated with graphene, effectively increase the silicon nanoparticles conductance between performance and mechanical stability. The silicon nanoparticles dispersed in graphene, good electrical properties, good mechanical stability, small volume effect to effectively reduce the change in volume of the electrode during charge and discharge, reduced the SEI surface of the electrode film due to the destruction of the change in volume, increase coulombic efficiency. In addition, the silicon nanoparticles outer coated graphene layer, can effectively prevent the aggregates of nano-silicon active substance, to further improve the Si/Graphene Composites loop stability. Electrochemical test data show that, Si nanoparticles graphene coated structure effectively increase the cycling performance of the silicon-based material, the charge and discharge rate of 100 mA/g 20 cycles still maintain the capacity of approximately 600 mAh/g, much better than Si nanoparticles graphene uncoated prepared lithium ion battery.