Electronic Design

Portable Power May Soon Mean More Than Batteries

Battery and power-component manufacturers recently got together at Power2000 to discuss some of the latest developments in battery and battery-charging technology. A number of presentations also examined how emerging portable and wireless applications will impact the demand for portable power. As the market forecasts indicate, portable products are becoming both more numerous and more sophisticated. The cell phones, laptops, and PDAs of today are morphing into the mysteriously named "smart phones," "handheld companions," and "vertical devices" of tomorrow.

Still, if the terminology is a little fuzzy, at least one message is clear: portable-equipment manufacturers will need more energy in smaller (but still safe) packages. This will enable them to meet customer demand for more functionally powerful products with longer runtimes.

Because Li-ion cells offer such a high energy density, there's a steady effort to move this technology ahead. On the high end, energy densities for Li-ion cells run about 330 to 340 wh/l with about 150 to 160 wh/kg in very thin prismatics. Some companies expect to push the volumetric energy density to 400 wh/l by next year. To do so, much tweaking of existing liquid Li-ion battery chemistry as well as the newer polymer-electrolyte chemistries will be necessary. Both are appearing in metal-film packaging that makes room for more active materials.

But these batteries may not be progressing fast enough to meet the projected demands for power. So work on alternatives to existing Li-ion cells goes on. Companies such as Moltech and PolyPlus continue their research on lithium-sulfur chemistries with the potential for much higher gravimetric energy density. In fact, Moltech is already sampling Li-S cells with 250 wh/kg.

Meanwhile, others are trying to develop alternative sources of portable power with higher energy or power densities. Fuel cells like those based on methanol are a promising example. These devices are said to offer three to five times the specific energy of Li-ion batteries and six to seven times the energy per unit mass. Fuel-cell developers and portable-equipment designers would like to take advantage of that potential.

At Power2000, four companies discussed their efforts to develop and commercialize fuel cells—a sign that interest in this technology is growing. Plus, it seems that fuel cells might be moving beyond the prototype stage. At least one vendor, Manhattan Scientifics, expects to deliver fuel cells to the portable marketplace by some time next year. Another vendor is Motorola Energy Systems, whose fuel-cell work with Los Alamos National Labs has been well publicized. Motorola says that commercialization of its technology is three to five years away. This doesn't mean, however, that we'll be throwing away our batteries anytime soon. When fuel cells do arrive, we might be using them in hybrid battery/fuel-cell systems.

The same may be true for supercapacitors, which are now used for memory backup. These multifarad devices could soon be showing up as main sources of power in low-current applications. Designers also envision them as battery helpers in devices that require pulsed power (think cell phone transmissions).

Benefits of the battery-supercapacitor combination include lower costs, reduced space and weight, and improved low-temperature operation of the battery. Similar gains may be achieved by joining supercapacitors with fuel cells. And as more of these hybrid power systems develop, designers should be more constrained by the limits of circuit technology and their imaginations, than by their power budgets.

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