The Strong Effect of Microporous Column Depth on the Lithiation-Delithiation Behavior in Si Electrodes for Li-Ion Cells and the Resistance to Mechanical Damage

Silicon microporous columnar structures possess inherent advantages for reversible lithium storage and high capacity, which make them attractive as potential negative electrodes for Li-ion batteries. This work demonstrates that a significant increase in Li storage capacity and cyclic performance can be achieved by increasing the depth of Si columns in the electrode. A set of electrodes with different column/pore depths were prepared by varying the etching time in direct electrochemical etching of (100) Si wafers. The other structural parameters, such as the porosity (52–60%) and Si mass fraction in the columns (0.40–0.48), were maintained nearly constant. The major finding of this work is that the specific capacity increased dramatically as the column/pore depth increased. Surprisingly, however, the post-cycling scanning electron microscopy (SEM) analysis indicated that the mechanical integrity of the electrodes during cycling increased with the column/pore depth. This improvement in mechanical stability of Si columns in the deeper columnar structure seems to explain the increased specific capacity and its stability over a large number of cycles.