Novel honeycomb silicon wrapped in reduced graphene oxide/CNT system as high-stability anodes for lithium-ion batteries

• Published in: Electrochimica acta 2019-09, Vol.317, p.583-593
• Main Authors: Wei, Qin, Liu, Gui-Cheng, Zhang, Chi, Hong, Xu-Jia, Song, Chun-Lei, Yang, Yan, Zhang, Min, Huang, Wei, Cai, Yue-Peng
• Format: Article
• Language: English
• Subjects: Anodes; Carbon nanotubes; Electrode materials; Electrodes; Graphene; Graphene oxide/carbon nanotube; Heat treatment; Honeycomb silicon; Lithium ion battery; Lithium-ion batteries; Magnesiothermic reduction; Nanoparticles; Rechargeable batteries; Self-standing anode; Silicon
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2019.06.024

Silicon (Si) has been regarded as one of the next-generation anode materials due to its ultrahigh theoretical capacity, low equilibrium potential, abundant resources and superior safety performance. Herein, we fabricated a novel honeycomb Si composed of many Si nanoparticles (NPs), which can be refined from the urchin-like crude product obtained through the magnesiothermic reduction process. Via the electrostatic attraction, rapid freeze-drying process and further thermal treatment, the honeycomb Si can be tightly encapsulated in a thin layer composed of reduced graphene oxide and carbon nanotube (indicating as Si-rGO/CNT) to avoid direct exposure to the electrolyte. Si NPs with the wrinkled rGO/CNT wrapping layer containing mesopores can not only shorten the pathway of Li+ ions and electrons but also accommodate the unavoidable expansion/contraction and buffer the excessive stress. Meanwhile, the CNT intertwined throughout the electrode can effectively repair those areas that lost conductivity during long-term cycling. Therefore, the self-supported Si-rGO/CNT electrode having a high Si content of 76 wt% exhibits capacities of 1304 mAh g−1 at 2 A g−1 and 1053 mAh g−1 at 5 A g−1 in rate performance, and maintain a capacities of 1899 mAh g−1 at 0.5 A g−1 after 250 cycles and 1003 mAh g−1 at 4 A g−1 after 1000 cycles accompanying with a stable coulombic efficiency (CE) up to 99.5%. A novel honeycomb Si composed of numerous Si nanoparticles is formed by the magnesiothermic reduction process after removing unreacted SiO2 and byproducts of Mg2Si. Via the electrostatic attraction, rapid freeze-drying process and further thermal treatment, honeycomb Si can be tightly encapsulated in a thin reduced graphene oxide/carbon nanotube layer to fabricate a self-supported Si-rGO/CNT electrode for lithium-ion batteries, exhibiting outstanding rate performance and high stability. [Display omitted] •Honeycomb Si composed by many Si nanoparticles can be obtained after removing the byproducts of Mg2Si.•Buffer space in honeycomb Si can buffer volume change.•Thin rGO/CNT layer can avoid direct exposure to electrolyte and help to the infiltration of electrolyte.•CNTs in electrode can repair those areas that may lose conductivity.•Self-standing electrode exhibits a stable coulombic efficiency.