Synthesis Of Core-Shell Silicon Carbide Composites And Its Application In Lithium Ion Batteries

Silicon has long been considered as one of the most promising anode materials for its advantage of high theoretical capacity low and environmental friendliness.Silicon will show a serious volume effect during charging and discharging,which will easily result in powdering of silicon particles and destruction of the conductive network inside the electrode,which seriously restricts its commercial application.The volume change of carbon material during charging and discharging is very small,and it has good cycle performance.Carbon itself is a mixed conductor of lithium ions and electrons;but its capacity is relatively small,so carbon materials are often used as high-energy anode matrix material.The lithium-insertion potential of silicon is combined with carbon material,so silicon and carbon are combined,which not only maintains a relatively high specific capacity,but also improves the volume effect of siliconr,thereby increasing its electrochemical stability and achieving the complementary advantages of silicon and carbon.In this paper,a silicon-oxygen compound was prepared using a low-temperature oxygen diffusion method.The Si expansion rate is calculated as 3 times of its own volume.That is,when the volume of SiO2 is greater than or equal to 3 times of Si volume,the expansion of Si will not cause the expansion of the entire Si/C particle volume during the charge and discharge of Li+.That is,the volume of Si/C particles does not change significantly.Calculated x = 1.145,that is,the silicon oxide waste weight gain is about 65.1%,the corresponding process conditions:in the muffle furnace at 800? for 10h.Resorcinol-formaldehyde(RF)as a carbon source for coating,after hydrofluoric acid etching,a silicon-carbon composite with yolk-hell structure.The results showed that the performance of Si/C anode material did not decrease significantly after 500 cycles,and its capacity remained above 1250mhA/g,and its average coulombic efficiency reached 99.5%.Due to the disadvantage of large specific surface area of the formed carbon-silicon composite carbon layer,secondary asphalt coating was used.The study shows that the specific surface area of the coated Si/C material after secondary coating has been reduced to a great extent.The average specific surface area is 98m2/g.After the secondary coating of asphalt and high-temperature carbonization,the Si/C material is used.The surface forms a relatively continuous char layer.The stability of the silicon-carbon-she structure was enhanced,and the amount of resorcinol-formaldehyde(RF)was increased to form a thicker C layer.In order to speed up the test progress and close to the industrialization effect,the anode material is 20%Si/C + 80%graphite.The results showed that the charge and discharge tests were performed at a current density of 0.2 C.The post-nano-Si/C composite(Mixed with 80%graphite)exhibited good cycle performance.After 40 cycles,the reversible specific capacity was above 400mAh/g,and the specific capacity retention rate was 95%.For the waste liquid produced by the above reaction,silica and fluoride ions were recovered by the ammoniating method,the atomic utilization rate was improved,and green chemistry was realized.