Scalable Synthesis of Porous Silicon by Acid Etching of Atomized Al–Si Alloy Powder for Lithium-Ion Batteries

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Abstract
Si anodes have attracted considerable attention for their potential application in next-generation lithium-ion batteries because of their high specific capacity (Li15Si4, 3579 mAh g-1) and elemental abundance. However, Si anodes have not yet been practically applied in lithium-ion batteries because the volume change associated with lithiation and delithiation degrades their capacity during cycling. Instead of considering the active material, we focused on the structural design and developed a scalable process for producing Si anodes with excellent cycle characteristics while precisely controlling the morphology. Al-Si alloy powders were prepared by gas atomization, and porous Si with a skeletal structure was prepared by leaching Al using HCl. Porous Si (p-Si12, p-Si19) prepared from Al88Si12 and Al81Si19 comprised resinous eutectic Si, and porous Si (p-Si25) prepared from Al75Si25 comprised lumpy primary Si and resinous eutectic Si. The porosity of the Si anodes varied from 63% to 76%, depending on the Si composition. The p-Si19 anode displayed the finest pore distribution (20-200 nm), excellent rate characteristics, a reversible discharge capacity of 1607 mAh g-1 after 200 cycles at a rate of 0.1 C with a Coulombic efficiency of over 97%, and high stability. The performances of the p-Si25 and p-Si19 electrodes began to decrease after 250 and 850 cycles, respectively, with a constant-charge capacity of 1000 mAh g-1 and at a rate of 0.2 C. In contrast, the p-Si12 anode maintained its discharge capacity at 1000 mAh g-1 for up to 1000 cycles without degradation. Therefore, the developed manufacturing process is expected to produce porous Si as an active material in lithium-ion batteries for high capacity and long life at an industrial scale.

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