Effort to Reduce Battery Weight May Soon Hit Brick Wall
Industry and military scientists continue the search for lighter and more efficient batteries, with a renewed focus on reducing loads carried by soldiers that affect their mobility and health.
Batteries, particularly those that power communication systems, are heavy and in many cases are single-use. Using new materials and power-regulation devices, engineers have been able to improve incrementally on the traditional lithium-ion batteries used by U.S. troops, providing a commodity that has proven as vital as ammunition in modern warfare.
“Power is most often taken for granted because everyone expects it to be there,” said Kooshiar Deylami, lead general engineer for the power and environmental engineering branch of the Army’s Communications-Electronics Research, Development and Engineering Center. “But it is one of the most important things a soldier can have.”
While strides are being made to lighten power sources, some researchers are concerned that batteries alone cannot solve the load problem because their construction is determined by scientific principles that are not easily circumnavigated.
CERDEC is focused on soldier power, but is taking a holistic approach to providing power to the battlefield to include more efficient generator and power-grid systems.
Breakthrough technologies like the Soldier Worn Integrated Power Equipment System, or SWIPES, have already been fielded. About the size and shape of a single body armor plate, the system’s rechargeable battery fits into a soldier’s vest and trickle-charges all of the electronics he or she is carrying using a high-density Zinc-air battery. The system conserves energy by keeping the devices fully charged at all times through a managed “trickle” of electricity from the central battery, requiring fewer charges and reducing battery weight by up to 30 percent.
Deanna Tyler, an electronics engineer with CERDEC’s battery technology development team, said the Army is moving toward adoption of hybrid power systems that can draw a charge from several sources.
“Many times, when people think power, they think batteries, which is certainly a large and important component,” Tyler said. “But many of our requirements are based on operational reality where small units or individuals or [forward operating bases] dictate the power sources that are required.”
But better batteries alone can’t solve the problem of supplying efficient and sufficient energy to troops in the field, said Marnie De Jong, lead engineer for CERDEC’s renewable energy team, power generation and alternative energy branch.
“Almost everything a soldier carriers right now has some sort of batteries and electronic component,” De Jong said. “When you look at it, there’s a whole family of solutions we need to apply to the soldier to best fulfill the soldier’s needs. We need different kinds of batteries and other power technologies customized to each area the soldier would need.”
The Defense Department invested at least $2.1 billion in power sources from fiscal year 2006 through fiscal year 2010, a December 2010 report by the Government Accountability Office said. That figure includes procurement, research and development and logistics support for batteries, fuel cells and capacitors, the report said.
Fuel cells and batteries were by far the largest categories.
“This amount will likely rise because of growing war fighter energy and power demands as well as interest in smaller, lighter, and more capable power sources,” which are “a mission-critical technology and may ultimately affect the warfighter if DoD is unable to meet demand,” the report said.
That investment line item is expected to increase because of a rise in the military’s reliance on advanced weapon systems and equipment and ongoing efforts to develop new technologies that are smaller, lighter, and more power dense, the GAO report said.
The suite of technologies extends to renewable energy sources, more-efficient generators and nano-grid technology for supplying those storage devices with power.
On base, a soldier can charge batteries fairly easily by plugging them into a generator or other power source like a solar array. Rechargeable batteries inherently lighten the load because soldiers don’t have to carry spares. But they must have a way to recharge batteries on the go.
Enter another CERDEC program that, along with SWIPES, has been selected as a top-10 Army technology of the year. The rucksack enhanced portable power system, or REPPS, is a foldable, portable, 10-pound battery recharging station that uses 62-watt solar panels.
The Marine Corps has similar systems.
Using the digital tactical communication system and a new self-repeating, self-healing TrellisWare radio, two communication devices can now do the work currently done by four types of radios, said Brig. Gen. Mark Wise, commander of the Marine Corps Warfighting Lab.
The batteries used by those two radio sets are half the size of the one powering current sets, last twice as long and are all rechargeable, Wise said.
Maj. Gen. John Toolan, who recently returned from Afghanistan as commander of the 2nd Marine Division, said reducing soldier loads was a priority for the service.
“We’re still carrying around these big, hunkin’ things and the new rechargeable batteries are just as heavy as the older batteries,” he told National Defense. “We’ve got to keep lightening the load. That has to be a priority with batteries in the future.”
A typical combat load is around 100 pounds of gear for a single soldier, including batteries, ammunition, rations and other supplies. That’s too heavy, combatant commanders agree. Battery technology is one area where pounds can be cut using new technologies and higher-density, more efficient fuel cells.
“When you start talking about Marines out there in the field having to hump hundreds of pounds of batteries to ensure that we’ve got the equipment in operating order throughout the duration of the patrol, [battery weight] becomes huge,” said Wise.
Batteries can only be as small and lightweight as the energy density of their core materials allows. Physics and chemistry will eventually dictate just how small they can become, said George Solhan, director of Marine Corps science and technology at the Office of Naval Research.
“I gotta tell you, though, that batteries are only going to get about 10 to 15 percent lighter, because the periodic table is the periodic table, ” Solhan said at a recent National Defense Industrial Association conference on reducing Marine Corps equipment weight. “Lithium is the most energetic element with the most electrons in the outer band and there aren’t any more elements like lithium. So, there is a limit as to how light batteries are going to get.”
Still, scientists will be able to make batteries incrementally more efficient, he said.
ONR is researching air cathodes to lighten batteries. Lithium-air batteries have a high energy density while using external oxygen instead of storing an oxidizer internally, making them lighter.
Nanosys, a Palo-Alto, Calif., company with 800 patents in nano-scale technologies, is working to create battery materials that are more energy dense than in their natural state, said Vijendra Sahi, vice president of government affairs.
The BB2590 military battery can provide 140 watt hours of energy per kilogram, about the same density of the battery in an Apple iPad, Sahi said. Using nanotechnology, the company has achieved materials that provide up to 290 watt hours per kilogram, giving them twice the run time for the same weight or half the weight for the same run time.
By 2015, Nanosys hopes to create materials for electric vehicle batteries that will provide 420 watt hours.
“By that time, you’re talking about batteries that can be three times lighter than current batteries,” Sahi said. “Plus, the cost of these batteries drops substantially as you increase the energy density.”
There are challenges to creating such compact batteries. As scientists figure out how to cram more energy density into smaller packages, the batteries become more volatile.
“Whenever you drive energy density higher in a battery, you have to do more to make it safe,” Sahi said. “We’ve resolved most of those issues. We need to be more conscious of it, but those are solvable engineering problems.”
As batteries continue to shrink, companies can also achieve economies of scale that will make them cheaper. Defense Department spending on batteries could triple in the next five years as various new applications are realized, Sahi said.
“The reason we all have smartphones and the reason that tablet computers even exist in the forms that they do is because batteries have gotten better,” he said. “The same goes for [the Defense Department]. As batteries become smaller and cheaper, there will be more ways to use them, like in lighter weight [unmanned aerial vehicles] that can be shoulder launched and still have long endurance.”
For all the research on batteries, little progress is being made and the low-hanging fruit may have been picked, said David Karcher, director of energy systems at Marine Corps Systems Command.
“We certainly don’t see tremendous or large improvements in batteries,” Karcher said at the NDIA conference. “But we believe there are some improvements to be made and there are some good research organizations that are taking a look at that.”