Evolution of the 3D Microstructure of a Si-Based Electrode for Li-Ion Batteries Investigated by FIB/SEM Tomography

The evolution with cycling of the three-dimensional (3D) microstructure of a silicon/carbon/carboxymethylcellulose (Si/C/CMC) electrode for Li-ion batteries is investigated by combined focused ion beam (FIB) / scanning electron microscopy (SEM) tomography. Using appropriate image processing methods, a volume of 20 × 8 × 11 μm 3 is reconstructed in which the Si and pore phases are clearly identified. Their respective morphological characteristics (volume fraction, spatial distribution, size, connectivity, and tortuosity) are determined before and after 1, 10 and 100 cycles. The Si particles (37 vol.%, median diameter = 0.37 μm) and pores (57 vol.%, median diameter = 0.40 μm) are homogeneously distributed and fully connected in the pristine electrode. Major changes in the electrode morphology occur upon cycling due to electrode cracking and the growth of the solid electrolyte interphase (SEI) layer. It also appears that the size and shape of the Si particles change upon cycling. After 100 cycles, they display a non-spherical morphology (axial ratio of 4.6) with a median size of 0.14 μm.