Encapsulating biomass-derived SiOx with internal conductive channels in nitrogen-doped flexible carbon cages for high performance Li ion-battery anodes

Abstract

The facile fabrication of high-performance silicon-based materials from natural and inexpensive biowaste has recently received great attention. However, the inevitable formation of SiC and the waste of organic ingredients limit their practical applications. Herein, an N-doped flexible porous carbon cage encaplusated SiO_x/C composite (p-NC/SiO_x/C-3) was synthesized by a magnesiothermic reduction combined with freeze drying strategy using rice husk as both the silicon and carbon source. The ingeniously designed indirect contact biomass carbon/SiO₂ interface can prevent the formation of SiC during the reduction process and induce the construction of continuous high conductivity internal channels. When utilized as an anode for lithium-ion batteries, p-NC/SiO_x/C-3 delivers a high capacity of 725.1 mA h g⁻¹ after 50 cycles at 0.1 A g⁻¹ with a volume expansion of only 12.3%. The electrode can still achieve 72% capacity retention after 400 cycles at 1 A g⁻¹. Ex situ SEM images and XPS results demonstrate that the high conductivity internal channels and N-doped flexible porous carbon cages derived from organic biomass and polymers can guarantee favorable structural integrity and the rapid formation of stable solid electrolyte interphase (SEI) films during repeated charge/discharge processes. Furthermore, the assembled LiFePO₄∥p-NC/SiO_x/C-3 full cell shows a high capacity of 116.2 mA h g⁻¹ after 100 cycles at 0.1 A g⁻¹ with an energy density of 419 W h kg⁻¹. These results give an insight into the green fabrication of high-performance silicon-based anodes for next generation lithium-ion batteries.