Effect of the pillar size on the electrochemical performance of laser-induced silicon micropillars as anodes for lithium-ion batteries

Silicon micropillars with tunable sizes are successfully fabricated on copper foils by using nanosecond-pulsed laser irradiation and then used as anodes for lithium-ion batteries. The size of the silicon micropillars is manipulated by using different slurry layer thicknesses ranging from a few microns to tens of microns. The effects of the pillar size on electrochemical properties are thoroughly investigated. The smaller the pillars, the better the electrochemical performance. A capacity of 1647 mAh g^-1 at 0.1 C current rate is achieved in the anode with the smallest pillars, with 1215, 892, and 582 mAh g^-1 at 0.2, 0.5, and 1.0 C, respectively. Although a significant difference in discharge capacity is observed in the early period of cycling among micropillars of different sizes, this discrepancy becomes smaller as a function of the cycle number. Morphological studies reveal that the expansion of micropillars occurred during long-term cycling, which finally led to the formation of island-like structures. Also, the formation of a solid electrolyte interphase film obstructs Li⁺ diffusion into Si for lithiation, resulting in capacity decay. This study demonstrates the importance of minimizing the pillar size and optimizing the pillar density during anode fabrication.