Enhanced lithiation and fracture behavior of silicon mesoscale pillars via atomic layer coatings and geometry design

Crystalline silicon nanostructures are commonly known to exhibit anisotropic expansion behavior during the lithiation that leads to grooving and fracture. Here we report surprisingly relatively uniform volume expansion behavior of large aspect-ratio (∼25), well-patterned, n-type (100) silicon micropillars (∼2 μm diameter) during the initial lithiation. The comparison results with and without atomic layer metal oxides (Al ₂O₃ and TiO₂) coatings reveal drastically enhanced solid electrolyte interphase (SEI) formation, higher volume expansion, and increased anisotropy. Square-pillars are found to exhibit nearly twice volume expansion without fracture compared to circular-pillars. Models are invoked to qualitatively address these beneficial or detrimental properties of silicon for lithium ion battery. Our experiments and computer simulations point at the critical relevance of SEI and pristine geometry in regulating volume expansion and failure. ALD-coated ultrathin metal oxides can act as an ion channel gate that helps promote fast Li⁺ transport into the bulk by changing the surface kinetics, suggesting new ways of designing electrodes for high-performance lithium ion battery applications.