Introduction: The worldwide thirst for portable consumer electronics in the 1990s has had enormous impact on the ﬁeld of portable power sources. During this era, lithium-ion batteries, which are based on having lithium ions shuttle between an insertion cathode and an insertion anode, emerged as the rechargeable power source for several lucrative portable electronics markets, including laptops and cell phones. | ELECTRODES Contents 3-D Electrodes Batteries Nanoelectrodes Ion-Selective Electrodes Porous Electrodes Semiconductor Electrodes 3-D Electrodes Batteries H-S Min and B Dunn University of California Los Angeles UCLA Los Angeles CA USA 2009 Elsevier . All rights reserved. Introduction The worldwide thirst for portable consumer electronics in the 1990s has had enormous impact on the field of portable power sources. During this era lithium-ion batteries which are based on having lithium ions shuttle between an insertion cathode and an insertion anode emerged as the rechargeable power source for several lucrative portable electronics markets including laptops and cell phones. The need for portable power is not diminishing. Moreover with the continued miniaturization of electronic devices and the development of microsystems there is considerable concern as to how future portable power systems will shrink to the dimensional scale of the device. For the most part batteries based on traditional designs have not been very successful at reducing size and still being able to provide adequate power and energy for portable electronics applications. The limitations faced in miniaturizing batteries are perhaps best shown by considering rechargeable lithium-ion batteries whose usage is ubiquitous. Lithium-ion batteries use insertion processes for both the positive and negative electrodes leading to the term rocking chair battery. The transport of lithium ions between the electrodes usually arranged in a parallel-plate configuration is one-dimensional 1-D in nature. To minimize power losses resulting from slow transport of ions the thickness of the insertion electrodes as well as the separation distance between them is kept as small as possible. This approach may appear counterintuitive in the effort to produce a useful battery because reducing the thickness of the electrode results in lower energy capacity and shorter operating time. Thus battery design involves a compromise .