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The carbon-microelectromechanical systems (C-MEMS) microfabrication process offers a promising method for fabricating three-dimensional (3D) battery architectures. In the current study, this approach was extended to the fabrication of positive electrode arrays and their assembly in a 3D lithium-ion microbattery. The positive electrode array was fabricated by electrochemical deposition of dodecylbenzenesulfonate-doped polypyrrole (PPYDBS) on an array of carbon rods. Electrochemical measurements show that the electrodeposited PPYDBS electrode array reversibly intercalates lithium with better gravimetric capacity than that of 2D electrodeposited films. The prototype carbon/PPYDBS 3D battery was based on an interdigitated electrode array configuration. It functioned as a secondary battery but the performance was limited because of electrical shorting. These initial results with the 3D interdigitated battery help to identify the needs associated with different electrode fabrication approaches and specific 3D designs.

Silicon-micromachining techniques have been combined with conventional material-synthesis methods to develop microelectrodes for 3-D microbatteries. The resulting electrodes feature an organized array of high-aspect-ratio microscale posts fabricated on the current collector to increase their surface area and volume for a given footprint area of the device. The diameter of the posts ranges from a few micrometers to a few hundred micrometers, with aspect ratios as high as 50. The fabrication approach is based on micromolding of the electrode materials and subsequent etching of the mold to release the electrode structures. Deep reactive-ion-etching or photo-assisted anodic etching has been used to form an array of deep holes in the silicon mold. Electroplating or colloidal-processing method has been used to fill the mold with battery-electrode materials. Measurements on electrochemical half-cells indicated that the 3-D electrode arrays, which are composed of vanadium oxide nanorolls or carbon, exhibited much greater energy densities (per-footprint area) than that of the traditional 2-D electrode geometries. The use of electroplating enabled us to fabricate 3-D interdigitated arrays of nickel and zinc; and battery operation was demonstrated. [2006-0293].

We investigated sp2 carbon microrods resulting from the reaction of lithium with hexachlorobenzene. The material exhibits high surface area (200–340 m2/g, depending on heat treatment) and a reversible lithium storage capacity in excess of 500 mA h/g. The discharge/charge behavior of the material resembles that of high specific capacity non-graphitic carbon. Without distinguishable plateaus, the reversible intercalation of lithium occurs at a broad potential window below 1 V vs. Li/Li+. A possible mechanism for the rod formation, based on SEM results, is briefly considered.

A general micro-molding approach based on MEMS fabrication has been introduced to fabricate 3-dimensional (3-D) electrodes for microbatteries. Batteries based on 3-D microstructure are shown to offer significant advantages (e.g., small areal footprint and short diffusion lengths) in comparison to the conventional 2-D thin film batteries. In this paper, microelectrodes for Li-ion and Ni-Zn batteries have been fabricated and testedCopyright © 2004 by ASME

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We have demonstrated that carbon-microelectromechanical systems (C-MEMS), in which patterned photoresist is pyrolyzed in inert environment at high temperature, constitutes a powerful approach to building 3D carbon microelectrode arrays for 3D microbattery applications. High aspect ratio carbon posts (>10:1) are achieved by pyrolyzing SU-8 negative photoresist in a simple one step process. Lithium can be reversibly charged and discharged into these C-MEMS electrodes. Because of the additional volume of the posts, higher capacities are achieved with the 3D array electrodes as compared to unpatterned carbon films with the same projected electrode area. These novel electrode arrays represent one of the critical components for 3D batteries, which may be interconnected with C-MEMS leads to enable smart power management schemes.