Anodized macroporous silicon anode for integration of lithium-ion batteries on chips

Macroporous silicon membranes were investigated as anodes for potential integration of lithium-ion batteries on chips. Free-standing and partially etched porous silicon membranes were fabricated from a p-type silicon wafer by using electrochemical anodization. Free-standing porous membranes were achieved with high aspect ratio of 40, average pore size of 1 μm, porosity around ∼70%, and wall thickness of less than 0.1 μm. Lithium storage capacity was quantified by galvanostatic discharge/charge measurements, showing specific capacity of 1425 mAh/g with Coulombic efficiency of 81% in the first discharge/charge cycle. The discharge/charge capacity was reduced as the charge rate increased, and the capacity fading was much less pronounced at high charge rate. Morphological analyses showed an increase of surface roughness and reduction of porosity after lithiation/delithiation cycling.