Designing 3D Conical-Shaped Lithium-Ion Microelectrodes

The effect of geometry on the power density and chemical stresses is assessed for a half cell three-dimensional LiCoO2 cathode structure. Simulations demonstrate that for an individual unit cell, as the aspect ratio of the 3D structure increases, its charge capacity decreases by 50%, but its structural integrity improves by approximately 40% as compared to its thin film counterpart. Calculations show that the constructive superposition of an array of conical structures can provide an enhanced instantaneous power density, in agreement with experimental results. This effect occurs because the back of the electrode is electrochemically shielded by the electrochemically active 3D tip. Mechanically, during galvanostatic discharge, chemical stresses become tensile at the electrolyte vertical bar electrode tip interface and more compressive at the electrode back contact interface, as a result of the electric field focusing at the tip of the 3D structure. When the aspect ratio of the 3D structure increases, the conical structure mechanically relaxes the substrate, thus reducing the possibility of mechanical failure-induced capacity loss. A critical aspect ratio that maximizes the discharge stresses, xi'=0.32 was identified. (C) 2013 The Electrochemical Society. All rights reserved.