Shape evolution of patterned amorphous and polycrystalline silicon microarray thin film electrodes caused by lithium insertion and extraction

Silicon is the most promising high capacity anode material to replace graphite for developing next generation high energy density Li-ion batteries. In this approach, patterned amorphous and microcrystalline Si thin film electrodes (a-Si and mu c-Si) have been prepared by rf-sputtering and etched further by a reactive ion etching (RIE) system to form square-shape microcolumn electrodes with controllable size (5 x 5 mu m width, 500 nm height, aspect ratio of width/height is 10:1) and array distance (5 mu m). It has been found that the volume expansion and contraction of a-Si and mu c-Si are anisotropic, about 180% along vertical direction and 40% along lateral direction. The total volume variation changes linearly with the increase of lithium insertion content up to similar to 310% for a-Si and similar to 300% for mu c-Si. It occurs nearly reversibly. In addition, it is observed that the original square-shape Si column transforms into the domelike appearance after lithium insertion and changes into bowl shape after lithium extraction gradually. Radial-like curved cracks are formed after 5-10 cycles and the neighboring Si columns tend to merge together when the distance of the columns is less than 1 mu m. (C) 2012 Elsevier BM. All rights reserved.