PNNL

Abstract

Silicon (Si) nanowires with a silicon oxide (SiOx) shell were observed in situ during lithiation and delithiation using transmission electron microscopy (TEM). The oxide shell constrains the volume expansion, which prevents full lithiation of the nanowire and retention of a crystalline Si core. Pores form in the amorphized silicon upon the first delithiation. We propose that this is caused by a high barrier to vacancy migration in the SiOx shell, which prevents vacancies formed during delithiation from transporting through the shell to the nanowire surface. These in situ studies demonstrate the importance of the direct observation of structural changes that occur in a material during cycling upon the addition of a coating.