Bird's nest-like nanographene shell encapsulated Si nanoparticles – Their structural and Li anode properties

Bird's nest-like nanographene shell (NGS) encapsulated Si@SiO₂ nanoparticles have been prepared by a simple chemical vapor deposition (CVD) method. The shell is comprised of a conformed coating with 4–10 layers of the nanographene, and nanographene spikes with the same thickness grown on the coating surface. The high crystallinity of the shell is demonstrated by XRD, HRTEM and Raman characterization. After SiO₂ has been removed, distinctive void space is created between Si core and nested NGS. Statistical estimation from TEM images of 50 Si@void@NGS particles shows that the volume of void space is about 2.82 times of that of Si nanoparticle, sufficient to accommodate volume change from Si to Li₁₅Si₄. Evaluation of Si@void@NGS for Li ion anode reveals a specific capacity of 2634 mAh g⁻¹ at a current density of 0.2 A g⁻¹, and an excellent rate and cycling performance. The capacity decreases by 5.2%–2497 mAh g⁻¹ after cycling at current densities of 0.5, 1, 2, 5 10, 20 A g⁻¹. The excellent performance can be attributed to high conductivity and high stability of the shell, which remains intact after repeated cycling.