Material Design of Silicon/Carbon Composite for High Performance Lithium-Ion Battery Anode

Abstract

Lithium-ion batteries (LIBs) have excellent performance and stability among energy storage devices and have been developed around small electronic devices and portable IT devices. In addition, it is applied to wearable devices, electric vehicles (EVs), and high-performance energy storage systems (ESSs) for power storage that can store electricity produced in eco-friendly manners like solar and wind power stations. Among them, EVs are striving for high-energy and high-power of batteries to surpass the diesel locomotive and become representative vehicles of the future. In particular, researches are being conducted on materials that are lighter, storing more lithium, and having high reactivity at the anode and cathode for improving the capacity and power in batteries. There are papers on high-capacity, high-power materials in LIBs. Currently, graphite is used as anode electroactive materials, but silicon materials that can increase energy density than graphite are spotlighted as next generation materials. Silicon materials have the advantages of 10 times theoretical capacity than graphite and low discharge voltage. However, compared to graphite, silicon react with a large amount of lithium, and have problems of volume expansion of more than 300%, delamination and pulverization of silicon particle, and formation of an unstable solid electrolyte interphase (SEI) layer. Therefore, batteries based on silicon anode materials can have a lot of capacity compared to graphite, but they are difficult to commercialized due to the rapid battery degradation in performance. In order to compensate the defect and secure stable performance, researches on forming a conductive carbon surface based on high-capacity silicon materials have been proposed to realized a high capacity energy density battery. However, the physical silicon and carbon integration could not withstand the stresses caused by silicon volume expansion and was easily broken. In this graduation research, randomly bonded silicon and carbon is synthesized at the molecular unit level. The materials showed a phenomenon of dissociation and reclustering through electrochemical reactions with lithium. It reacted with lithium several times to decomposed the bonds of amorphous silicon and carbon to stabilize several nanometer silicon particles with carbon framework. Stabilized silicon and carbon composites form a stable SEI layer and the carbon framework acts as a buffer, showing stable battery cycles.