Insight into the solid electrolyte interphase on Si nanowires in lithium-ion battery: Chemical and morphological modifications upon cycling

The effect of lithiation-delithiation rate and of the number of cycles on the properties of Si nanowires (SiNWs) and electrolyte interface is presented in this paper. The surface and bulk modifications of SiNW electrode induced by electrochemical process of lithiation-delithiation were investigated by combined electrochemical tests (galvanostatic cycling), field emission gun scanning electron microscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. Low lithiation-delithiation rate improves electrochemical performance due to a better penetration depth of lithium into the SiNW electrode and the formation of a homogeneous solid electrolyte interphase (SEI) layer on the SiNWs after the first cycle. However, after repeated cycling, SiNWs suffered strong mechanical stress leading to a rough or porous SiNW structure covered by a porous SEI layer. This study highlights the SEI modifications caused by the lithiation-delithiation rate and the modifications of the Si electrode upon cycling.