The Preparation And Electrochemical Performance Study Of Nano/Micro-Hierarchical Structured Rice Husk-Derived Silicon Based Materials As Anodes For Lithium Ion Batteries

The research mainly focuses on the preparation and electrochemical performance study of nano/micro hierarchical structured rice husk-derived silicon based materials as anodes for lithium-ion batteries. Inspired by the ideas of fabricating nano/micro structure and preparing silicon/carbon composites, we used low-cost rice husk as raw material to prepare silicon nanoparticles via magnesiothermic reduction, and then utilized the rice husk-derived silicon nanoparticles to fabricate silicon/carbon composites with stable interface structure, thus improving the electrochemical performance of silicon anodes. This research can bring a great significance to the sustainable development of energy.In this paper, the research content mainly includes the following three aspects:1. Rice husks were utilized as raw material to prepare nano-Si（denoted as RH-Si） through magnesiothermic reduction. The structure and morphology of RH-Si were characterized by XRD, SEM, and BET. The results showed that the highly crystalline RH-Si had the granule morphology with an average of ⁵0 nm after magnesiothermic reduction. As anodes for lithium-ion batteries, the RH-Si could deliver a very high discharge capacity of 3006 mAhg^-1 in the first cycle; however the initial coulombic efficiency is just only 46%. To make matter worse, after only 17 cycles the specific capacity of RH-Si decreased to below 200 mAhg^-1.2. RH-Si nanoparticles were used as raw material to fabricate nano/micro hierarchical structured Si/N-doped carbon/carbon nanotube（denoted as SNCC spheres） through electrospray. The structure and morphology of SNCC spheres were characterized by XRD, Raman, TEM, and XPS etc. The results showed that the SNCC composite has uniform nano/micro hierarchical structured spheres morphology, with the diameters of 3.2 ± 0.8 μm. This unique hierarchical hybrid structure can not only contribute to the formation of stable SEI films, but accommodate the expansion of Si and contribute to fast electronic transport. Herein, the SNCC spheres exhibited excellent electrochemical performance as anodes for lithium-ion batteries. At the current density of 0.5 A g^-1, the SNCC spheres could deliver a high reversible specific capacity of 1380 mAhg^-1 in the first cycle, and still maintain 1031 mAhg^-1 after 100 cycles.3. RH-Si nanoparticles were used as raw material to fabricated Si/rGO composite through electrostatic interaction. The structure and morphology of Si/rGO were characterized by XRD, Raman, SEM, and TEM. The results showed that Si nanoparticles are uniformly dispersed in the surface of graphene. Compared with RH-Si, the Si/rGO exhibited enhanced electrochemical performance as anodes for lithium-ion batteries. The Si/rGO could deliver a discharge capacity of 2042 mAhg^-1 in the first cycle, and the initial coulombic efficiency is 55%. After 10 cycles, the specific capacity of Si/rGO could maintain 1001 mAhg^-1, while that of RH-Si was 297 mAhg^-1.