Preparation And Properties Of SiOC Compound/Exfoliated Graphite Anode Materials For Lithium Ion Battery

Along with the rapid development of hybrid car and portable electronic equipment, Lithium-ion battery is used widely, meanwhile there are higher request for the specific capacity and cycling stability. Now the anode materials of commercial lithium-ion batteries are graphite-based materials, the cycling performance of which is perfect but theoretical capacity(372mAh/g) is very low. So it is a research hotpot to develop new lithium-ion battery anode materials.SiOC compound has high specific capacity and simple synthetic process, but its cycle performance and electrical conductivity are bad. Exfoliated graphite(EG) is very soft, which could relieve volume change and increase electrical conducitivity of SiOC anode compound. Precursor is prepared by mixing hydrogen-containing silicone oil, cross-linking agent and exfoliated graphite. The comoposites of SiOC compound/EG are synthesized by heat treatment of this precursor for1h. The cracking process and pyrolysis product are analysed by XRD, SEM, TG and so on. Charge-discharge properties and cycle performance are studied with emphasis.DTA-TG curves indicate that the productivity of precursor is80%and quality loss mainly occurs between200℃to800℃, in which there are lots of break and rearrangement reaction; the FT-IR spectrum of SiOC compound/EG composites show that it is mainly composed of Si-O-C and Si-O groups; the XRD spectrum show that the composites is amorphous with diffraction peak of SiO2and SiC; from SEM photographs of the composites, we could see that most of the anode materials are irregular flakes with some small particles attached to large particles. Besides that we also find that graphite flakes are coated with a very thin layer of SiOC compounds, with some nanowire; EDX and XRF show that the mass fraction of Si, O and C are approximately46%,29%and25%.The first discharge capacity of SiOC can be almost1300mAh/g, but its cycle performance is bad. After compositing with EG, the first discharge capacity of anode materials decrease a little, but the cycling performance become better. This is mainly due to remission of SiOC compounds’volume expansion by soft exfoliated graphites. Voltage platform isn’t found in the charging procession of the first cycle and later cycles, which shows that in the process of Li+inserting anode materials there is no stable redox reaction.Adding aluminum powder into SiOC compound/EG composites can reduce its first discharge capacity but improve the cycle performance, and with the increasing amount of added Al, the initial discharge capacity become lower, meanwhile the cycle performance becomes better and better. The XRD spectrum of the anode materials with different amount of Al show that with the increaing amount of Al, more and more amorphous states can be found. Both of the first discharge capacity and cycle performance become better with the expansion rate of EG increase, and it is also found that when the EG is prepared by graphite row powder, the anode materials is better than others.The SiOC/EG composites prepared by a new kind of cross-linking agent glycol is also studied in this paper. TG-DTA indicates that the productivity of SiOC compound/EG is very slow. With the pyrolysis temperature become higher, the electrochemical of prepared anode materials become better and better. When the expansion of EG is47ml/g and the temperature of treatment is1200℃, the first discharge capacity of SiOC compound/EG anode materials is1354.4mAh/g, and the reversible capacity after60cycles still retains300mAh/g.