Mobile Phone Future Soldier Materials Handling 15 - 30 W Laptop Computers High - Energy Portable Fuel Cell Power Sources

Fig. 1. Portable power applications require high-energy power sources. The energy density requirement for portable power sources is ever on the increase. Technology companies are working to find ways to enhance the run time of mobile devices such as portable computers, MP3 players, and mobile phones. For example, the video-streaming offered in presentday mobile phones is a power-hungry feature that reduces the run-time for phones powered with even the most advanced of lithium-ion batteries. The U.S. military has also had a persistent demand for compact, long-life power sources for meeting the field needs of the soldier. The future-day soldier will be outfitted with high-tech electronics that significantly increase awareness of the combat environment. Radios, nightvision devices, portable computers, and personal cooling systems are all examples of power-hungry devices to be used by the future-day soldier. There are also other areas that need high-energy portable power sources: (a) extending the run-time of materials handling equipment, (b) meeting on-board power needs in recreational vehicles, and (c) powering remote electronics equipment. Achieving longer run-times will eliminate the need for the frequent replacement of discharged batteries, reduce the downtime resulting from recharging or replacing batteries, and eliminate the logistics needed for recharging batteries. Some of the applications of portable power sources and the corresponding power levels are shown in Fig. 1. For mobile devices, the energy density target is to increase the device run-time by five to ten times, without increasing the size or mass of the power source. A recent call for proposals from the U.S. Department of Energy (DoE) identifies these targets. To meet the energy and power density targets for future mobile devices, it would be desirable to achieve a specific energy of 500 Wh/kg or greater, an energy density of 1000 Wh/liter or greater, and a specific power not less than 50 W/kg. Typical power levels in mobile devices vary from 1-25 W with runtimes varying from 10 to100 h. Further, any next-generation power source for mobile devices must include battery features, namely, quiet operation, ruggedness, ease-of-use, operability in any orientation, operability over a wide temperature range (-40oC to +60oC), and operability in confined environments. There may also be other requirements such as underwater operation that are specific to military applications. For large portable systems such as those used in material handling equipment, the high-energy power source supplies the base load and charges a battery during the off-period or serves as a power back-up. Typical power levels for this category of applications vary from 50 to 1000 W and the power density can be as low as 10 W/kg. The target is usually to increase the run-time of large portable systems by at least five times the current values. The above requirements present significant technical challenges. However, in the last decade or so, there have been focused efforts in the commercial and government sectors to develop fuel cell based power sources operating on high-energy fuels such as hydrogen, methanol, and propane to meet the requirements of nextgeneration portable power sources.