Design and Fabrication of 3D Battery Electrodes

New generations of microscale devices that serve such application areas as sensing/actuation, communication and health monitoring will require power sources whose footprint areas are on the order of square millimeters. Three-dimensional (3D) battery architectures offer a novel approach capable of powering such devices by using the third dimension, height, to increase the amount of electrode material within a given footprint area. Moreover, by using 3D electrode designs which minimize the ionic path length between electrodes, there is the prospect of achieving high energy and power density within the small footprint area. In this paper, we report on the fabrication and properties of battery electrodes comprised of arrays of vertically-aligned carbon rods. Testing these arrays as negative electrodes for lithium ion secondary batteries shows that the electrodes exhibit good reversibility for lithium and achieve areal capacities greater than 5 mAh cm^-2 at a current density of 0.1 mA cm^-2, although there is capacity fade with cycling. The fabrication process demonstrated here offers the opportunity to tune rod dimensions and aspect ratios, the key design features which determine energy and power densities for 3D battery architectures.