In Situ and Ex Situ Transmission Electron Microscopy Study of Lithiation Behaviours of Porous Silicon Nanostructures

In this work, we study the lithiation behaviours of both porous silicon (Si) nanoparticles and porous Si nanowires by in situ and ex situ transmission electron microscopy (TEM) and compare them with solid Si nanoparticles and nanowires. The in situ TEM observation reveals that the critical fracture diameter of porous Si particles reaches up to 1.52 μm, which is much larger than the previously reported 150 nm for crystalline Si nanoparticles and 870 nm for amorphous Si nanoparticles. After full lithiation, solid Si nanostructures transform to crystalline Li₁₅Si₄ phase while porous Si nanostructures transform to amorphous Li_xSi phase, which is due to the effect of domain size on the stability of Li₁₅Si₄ as revealed by the first-principle molecular dynamic simulation. Ex situ TEM characterization is conducted to further investigate the structural evolution of porous and solid Si nanoparticles during the cycling process, which confirms that the porous Si nanoparticles exhibit better capability to suppress pore evolution than solid Si nanoparticles. The investigation of structural evolution and phase transition of porous Si nanostructures during the lithiation process reveal that they are more desirable as lithium-ion battery anode materials than solid Si nanostructures.