Preparation And Properties Study Of Lithium-ion Battery Silicon/Carbon Composite Anode Materials

Lithium-ion battery is a new energy storage medium, and it has high voltage, long cycle life, high specific capacity, low self-discharge rate, high security, environmental pollution, no memory effect and other excellent features. Currently, lithium-ion batteries have been widely used in mobile phones, laptops and other portable electronic devices and digital products. However, the conventional lithium-ion battery specific capacity is small, and it has been unable to meet the urgent needs of the people for a large-capacity lithium battery. Therefore, to develop new lithium-ion battery materials is imminent.Silicon anode material has the highest theoretical specific capacity (4200mAh/g), but it also has a lower lithium intercalation/deintercalation potential. Accordingly, the silicon material can be used to develop a new generation of lithium-ion battery, in order to increase its capacity. However, even if silicon materials have many advantages, the commercialization process has not been easy, because there will produce a huge volume expansion(>300%) during its cycle process. And although the specific capacity of the carbon material is small, but it has a better cycle performance and structural stability. Therefore, we can combine the advantages of silicon anode material and carbon anode material to prepare a new type of silicon-carbon composite anode which can be used for of lithium-ion batteries.Three methods were used to improve the performance of silicon monoxide, silicon monoxide microparticles and two different hollow core-shell silicon-carbon composites had been prepared. Morphology and structure was characterize by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and EDS spectroscopy, and the electrochemical performance was tested by Land test system.The milled silicon monoxide had a high specific capacity at 1814mAh/g during the first charge-discharge cycle, while its coulombic efficiency is low (50.04%). During ongoing capacity charge/discharge test the capacity would have a substantial loss, and after fluctuating the Coulomb efficiency would gradually increase. The coulombic efficiency was 99.2% in the end of the 60th charge-discharge cycle, and the specific capacity was 59mAh/g. This also proved that the milled silicon monoxide had a low specific capacity, which could not meet the application requirements and needed to be further modified.Hollow shell structure silicon-carbon composites were successfully prepared with citric acid as a carbon source by pyrolysis. Morphology test results showed that the optimum conditions for the preparation of the material is to maintain at 600℃ for 4 hours, and the best ratio between SiO and citric acid is 1:2.5. Electrochemical performance test results showed that Coulomb efficiency had an increasing trend when using 0.1C charge during the charge/discharge test, and when Coulomb efficiency got 95% the discharge capacity was 560mAh/g while the charge capacity was 530mAh/g.Another hollow core-shell structure silicon-carbon composites was prepared by chemical vapor deposition of acetylene carbon, and the best condition was first deposited at 600℃ for 20 minutes, and then warmed to 800℃ under the deposition for one hour. The electrochemical performance testing results showed that when using 0.1C in test, after five charge-discharge cycles Coulomb efficiency could reach more than 95%, and the discharge capacity was 806mAh/g, while the charge capacity was 769mAh/g. After 60 cycles Coulombic efficiency was 99%, and the discharge capacity was 409mAh/g while the charge capacity was 406mAh/g.