Silicon nanopillar anodes for lithium-ion batteries using nanoimprint lithography with flexible molds

The lithium ion battery, a preferred energy storage technology, is limited by its volumetric and gravimetric energy densities, as well as its capacity retention with prolonged cycling. In this work, the authors exploited the extremely high lithium storage capacity of Si as an anode material and tackled the issue of lithium-induced volume expansion by patterning the Si into a nanopillar array using nanoimprint lithography and reactive-ion etching. Arrays of 200 nm-pitch Si pillars of 50-70 nm diameter and 200-500 nm height were fabricated on stainless steel substrates, assembled into coin cells, and tested against lithium counter electrodes. Initial charge capacities in excess of 3000 mAh/g, and a low rate-dependence, were obtained with these Si pillar anodes. This represents an improvement over previously reported nanoimprint-patterned Si anodes. Though this initial capacity is roughly equivalent to previously reported values for bulk Si anodes, our nanopillar anodes exhibit far superior capacity retention with subsequent charge-discharge cycles. (C) 2014 American Vacuum Society.