In-situ Preparation And Investigation Of Silicon/carbon Composites From Rice Husk Used As Anode Materials Of Lithium Ion Battery

Lithium ion batteries have become an important energy storage device of portable electronic devices because of high energy density. However, emerging electric transportation systems require batteries having higher specific energy, energy density and better cycle life than traditional batteries. In many of the lithium ion battery anode materials, silicon is considered to be the most promising materials, because of its exceptionally high theoretical specific capacity, abundance in the earth’s crust, and the advantages of mature advanced manufacturing infrastructure. The research of silicon used in lithium ion battery has a history more than 30 years, but practical application of silicon has been greatly limited by bad cycling performance caused by the mechanical grinding and rapid capacity attenuation.Rice husk has the characteristics of low cost, high production, renewability, and is rich in a large number of carbon and silicon dioxide. Due to the above advantages, rice husk has caught the attention of researchers in the field of lithium ion batteries.In this paper, Rice Husk based silicon/carbon composites were in-situ prepared from rice-husks by directly carbonize-reduction(DC/R) process and alkali boiling-carbonize-reduction(AB-C/R) method. The corresponding products were named as RH-Si/C and AB-RH-Si/C respectively. In addition, Si/C composite was also prepared through AB-C/R method from the template carbon materials(derived from rice-husks in Jilin Kai Yu biomass utilization co., LTD.) with different ash content. The performance of these silicon/carbon composites as anodes shows as follows:First, rice Husk silicon(RH-Si) and RH-Si/C composites were in-situ prepared from rice husk by DC/R method, the main process of which was magnesiothermic reaction followed by directly carbonize step. Compared with the LIBs with the RH-Si as anodes, the LIBs with RH-Si/C anodes had better cycle stability and capacity retention. Besides, RH-Si/C with different ratios of silicon and carbon were prepared by controlling the temperatures of carbonization step. The electrochemical performance showed that: the LIBs with RH-Si/C all had good cycle stability and rate capability. Even after many cycles, the resistance of cell changed little. Nevertheless, RH-Si/C from DC/R method still had some defects, such as low specific capacity(the highest value only 90 mAh/g), fast capacity decay after the first Li-intercalated cycle, etc. Accordingly, there is no good market advantage for these composites as anodes in LIBs. So many more works need to be done.Second, based on the structure of rice husks, the silicon/carbon composites, namely AB-RH-Si/C, were in-situ prepared by AB-C/R method from rice husks. This main preparation process was described as follows: firstly, the silicon dioxide under skin layer of rice husk were removed by alkali boiling method, so the porous structures of vascular bundles/SiO2 inside rice husk was fully exposed; Secondly, uniform dispersion silicon/carbon composites were obtained via the reduction of silicon dioxide inside the vascular bundle of rice husk followed by the carbonization step. The capacity of LIBs with these AB-RH-Si/C anodes, 180 mAh/g, was twice than that of LIBs with RH-Si/C anodes and showed a better rate capability.Last, based on the AB-C/R method, the template carbon Si/C composites(TC-Si/C) and rice husk carbon Si/C composites(RH-Si/C) were prepared from template carbon and rice husk carbon, which were obtained from Jilin Kai Yu biomass utilization co., LTD. Like the TC-Si/C and RH-Si/C, the capacitive carbon(CC) from Kai Yu was also applied in LIBs as anodes. The results of electrochemical measurements show that: TC-Si/C had a superior electrochemical performance compared with RH-Si/C and CC. In addition, the different ash content of template carbon had an important effect on the performance of LIBs with TC-Si/C anodes. A higher specific capacity could be obtained when the ash content more than 10%. The TC-Si/C, all with low tap density, had been used as anodes to assemble full LIBs with LiCoO2 cathodes. During the assembly process, an aqueous adhesive, CMC, and non-aqueous adhesive, PVDF, were all used to assemble half cell together with TC-Si/C, and assemble full cell using PVDF with TC-Si/C. The full cells exhibited good capacity, although longer time was required so as to form stable SEI film. Due to the low cost of assembly system with aqueous adhesive, so this aqueous assembly system was more potential applying in LIBs.