Time Flies at Darnell’s nanoPower Forum

June 10, 2007 by Jeff Shepard

The last session on Tuesday afternoon at this year’s nanoPower Forum consisted of 5 papers focused on ’Batteries and Micro Fuel Cells.’ Scott Potter, Director of Jasper Wireless, commented, "I thought that was too many papers for a single session, but every paper was good. The time flew by and before I realized it, they were introducing the last speaker of the day."

EaglePicher, Varta Microbattery and Front Edge Technology all presented details of thin-film and micro batteries. Also during the Tuesday afternoon session, Fraunhofer Institute teamed with Varta Microbattery to discuss "A passive micro fuel cell with hydrogen generator as battery replacement" while researchers from Lawrence Livermore Laboratories presented a "MEMS-based reformed methanol fuel cell for portable power"

Dr. Robert Hahn, Head of the Portable Power Supply Group at the Fraunhofer Institute, started the session presenting a joint paper with Varta Microbattery. Dr. Hahn presented a detailed discussion of the technology involved in a new micro PEM fuel cell in combination with Zn/H2O hydrogen production. He also provided an efficiency evaluation of micro fuel cell systems at low power and pulsed discharge of a typical radio sensor node.

"The power supply is often the major show stopper in efforts to develop miniature systems," stated Dr. Hahn. "We have demonstrated 60% higher energy of the 4 cubic centimeter fuel cell system compared to alkaline batteries of same size. Three times higher energy (900 Wh/l) compared to alkaline cylindrical cells can be potentially achieved at low power drain."

Eddie Shaviv, President of Varta Microbattery followed with a presentation of "Thin-Film Lithium Polymer Batteries." In addition to a general discussion of Varta’s thin-film battery technology, Shaviv provided a brief description of an EU-funded project to develop a combined solar panel/thin-film Lithium-polymer battery system. The resulting 4V power system has been integrated into a portable weather sensing station.

"Varta are developing advanced primary and rechargeable lithium batteries for a variety of applications," Shaviv stated. "The use of a special epoxy resin for the cold lamination of our flat cell LFP25 primary system used in the ‘Smart Card Battery’ leads to excellent behavior during hard bending. The battery continued to function after more than 1,000 cycles in the ISO Bending Test. We are also developing advanced rechargeable lithium batteries with a blend of nano-scale Lithium-Silicon alloys combined with carbon nanotubes. The resulting batteries have a capacity of more than 1000mAh/g, three times that of graphite systems, and have demonstrated 90% capacity retention after 500 charge/discharge cycles."

Next on the Tuesday afternoon agenda was "A Micro Battery for Low Power Applications," presented by Christo Brand, Project Manager with EaglePicher. Designed for use in implantable medical devices, this hermetically-sealed micro battery employed a MnO2 cathode and metallic lithium anode. The battery diameter is 0.093" (2.37mm) and the length is 0.265" (6.73mm). Cell construction consists of a titanium casing (negative) with a glass to metal seal for the positive pin feed through. Weight is approximately 90mg.

"The very small diameter of this battery enables deployment via catheter instead of invasive surgery," according to Brand. "Our new cell design has a theoretical life of 15 years and is currently undergoing clinical trials in Europe."

Jeffrey Arias, Vice President with Front Edge Technology, described a family of thin-film solid-state rechargeable lithium batteries. The cell construction consists of a Lithium anode, an amorphous ceramic/polymer electrolyte and a nano-crystalline LiCoO2 cathode. Front Edge has produced over 150,000 thin-film cells to date in their facility in Baldwin Park, California. Front Edge has produced a wide variety of cells including a high-temperature battery designed for remote sensor applications. Called the "NX 0201" this unit delivers a capacity of 700µAh at 4.2 V in a 1-inch square by 0.006 inches thick package. It is designed to survive 2,000 temperature cycles from 20 to 150°C and is specified to operate at least 50 hours at 150°C.

The company’s largest single cell is the SCX1 that delivers up to 8 mAh at 4.2V. This 1" X 2.2" X 0.006" cell is designed to operate for up to 4 years, or 1, 460 charge/discharge cycles. Delivering only 0.12mAh at 4.2V, and measuring 1.9mm X 8.2mm X 0.12mm, the company’s smallest cell is still in development for use in medical implant applications. The company has also developed high-voltage (32V nominal) thin-film batteries, button cells and combined battery/solar cell systems that are only 0.2mm thick, including the solar cell.

The afternoon session concluded with Dr. Jeff Morse from the Lawrence Livermore National Laboratory, Center for Meso, Micro and Nano Technology, describing a "MEMS-Based Reformed Methanol Fuel Cell for Portable Power." According to Dr. Morse, the use of a microfluidic fuel processor enabled component scaling and integration sufficient to achieve power sources in the 2-10W range that are competitive in size and energy density in comparison to alternative power sources.

"While carbon monoxide tolerance of proton conducting membranes has typically limited the performance of reformed methanol fuel cells, phosphoric acid doped polybenzimidizole (PBI) membranes have been tested that exhibit no degradation for carbon monoxide greater than 2% mole fraction," Dr. Morse stated. "Further benefits of the PBI membrane include operating temperature of 150-200°C, and no need for water to assist protonic conduction. As a result, a chemically and thermally robust fuel cell power source can be realized."