Lithium Batteries in Bizjets Remain Scarce, But Are Coming
Only one business jet thus far has been certified with a lithium-ion main-ship battery, Cessna’s Citation CJ4, which employed lithium-iron phosphate technology, unlike the lithium-cobalt oxide chemistry in the Boeing 787 batteries. No other business jet has been certified with a lithium-ion main-ship battery, although Gulfstream had planned to employ a lithium-ion battery in the G650 before switching to a nickel-cadmium battery while the aircraft was still working its way toward certification.
There are plenty of questions surrounding the use of lithium-ion technology in aviation batteries, not just because of Boeing’s 787 problems but also because of a fire in a CJ4 battery, but it appears that lithium-ion main-ship batteries are well on the way to deployment in some business jets.
Cessna has applied for and been issued FAA special conditions for certification of lithium-ion batteries in the new Sovereign; similar conditions applied to the CJ4. Cessna also announced on Oct. 18, 2010, that it plans to install “dual lithium-ion batteries” in the new Citation X (formerly Ten); however, AIN could find no record of special conditions issued for the Model 750 (X) related to lithium-ion batteries. In the middle of least year, a Cessna spokeswoman told AIN that the new Citation X will have lithium-ion batteries.
The CJ4 initially shipped new with lithium-ion batteries, but not since the fire incident. In 2011, a ground-power charging unit caused a main battery fire on a CJ4, resulting in an Airworthiness Directive (AD) that mandated replacement with nickel-cadmium or lead-acid batteries. According to an FAA spokeswoman, the FAA discovered that [the CJ4 fire] was caused by a mechanic’s intentionally bypassing the safety systems built into the battery–“that’s why the fire occurred.”
Cessna engineers developed the CJ4 battery in house, using lithium-iron phosphate technology. According to an SAE International paper authored by Cessna’s Vernon Chang, Steven Waggoner and John Gallman (System Integration of a Safe, High Power, Lithium Ion Main Battery into a Civil Aviation Aircraft, November 2010), the 54-pound, 44-Ah lithium battery weighed 35 percent less than a comparable Ni-Cad battery. The lithium battery used 160 ANR26650M1 cells manufactured by A123Systems.
The Cessna engineers tested the battery to RTCA DO-311 explosion-containment performance standards, and they said that the hardest part was getting anything to ignite. Overcharging one cell did not cause explosion or combustion. By modifying the DO-311 procedure, the engineers were able to generate an explosion, but this included “introducing varying amounts of synthesized vaporized electrolyte gas into the battery to find a flammable fluid-to-air ratio” and installing a fan inside the battery case to mix air with the vaporized electrolyte. They concluded, “The only realistic, but highly improbable, scenario is for a rich concentration of vaporized electrolyte gas to leak out through the battery case seals during in-flight pressure altitude changes until the flammable fluid-to-air ratio for ignition existed. Even with this scenario, the gas would need to be evenly mixed inside the case and be ignited by a source, such as an arc from a loose bus bar, before an explosion [could] occur. This modified procedure was performed and the battery case successfully contained the explosion. No positive feedback thermal runaway, leading to a chain reaction of adjacent cells or sustained asymptotic rise in battery temperature, resulted after the explosion, mitigating the need for vent ports.”
Pilot Kevin Savord told AIN that his company flew a CJ4 for 100 hours with the lithium-ion battery before the AD required it to be replaced with a lead-acid battery. “Our lithium-ion battery worked well,” he wrote in an email, “with just one exception.” A high discharge during an avionics update tripped the battery’s health-monitoring computer, which needed to be reset. Unable to find someone who knew how to reset the battery quickly enough, he opted to replace the battery, which Cessna paid for. With the lithium-ion battery, engine starts were cooler than with the lead-acid battery, he noted. However, the lead-acid battery’s recovery time for the second start is near zero, he wrote, while “the lithium-ion took up to a minute-plus before the second start could commence.” Savord remains wary of lithium-ion technology: “Due to the ongoing saga with the 787 and the automotive horror stories, I am already shy of the technology to a point where I’m just not ready for it.”
There are few actual cases of fire problems with automotive lithium-ion battery systems, although problems that have occurred get blown out of proportion and spread far and wide via the Internet. Lithium-ion batteries on the Chevy Volt and Tesla Model S are liquid-cooled, which seems to be effective. A fire in a Chevy Volt battery system occurred after breaching of the liquid cooling system.
AIN asked Cessna to clarify its plans for lithium-ion batteries in new jets, and a spokesman responded: “All batteries in use on Cessna aircraft are in full compliance with FAA regulations. Any future lithium ion battery usage will be subject to FAA certification as is the case for any other part of the aircraft.”
Main Ship Battery Coming from EaglePicher Technologies
Joplin, Mo.-based EaglePicher Technologies has been developing lithium-ion battery technology for the past two decades and expects to have a lithium-ion main-ship battery certified and installed on an aircraft by year-end, according to Ron Nowlin, vice president and general manager of the company’s Aerospace Systems division. Nowlin declined to identify the aircraft type in which this battery will be installed, and he said that he “cannot confirm” other news reports that it is for a Cessna jet.
The EaglePicher battery chemistry is lithium-iron phosphate, using cells manufactured by an unidentified partner-supplier (not A123Systems). Lithium-iron phosphate, he said, “is a little more thermally stable” than lithium-ion cobalt technology, which is used in the Boeing 787 battery and Tesla electric automobiles. The EaglePicher aircraft battery weighs 40 percent less than a comparable Ni-Cad battery and is housed in a stainless steel container with a top-mounted heat sink “to keep heat generation down during the charge cycle,” Nowlin explained. The battery management system consists of primary and secondary electronics so that if the primary protection circuit fails, the secondary can take over. If both systems fail, the battery must withstand a DO-311 explosion containment test. “This requires that you charge a cell in the pack to the point that it ruptures or vents,” he said. “And you have to ignite the electrolyte. It [then] can’t release flame, electrolyte or particles outside the battery enclosure.”
EaglePicher’s battery has passed initial DO-311 tests and will be subjected to further testing with validation by an FAA designated engineering representative before certification. The company is targeting aircraft manufacturers first but also plans to offer lithium-ion main-ship battery technology to the aftermarket, according to Nowlin.
It’s not just lithium-ion battery technology that has had problems with fire and thermal runaway. Ni-cad batteries faced their own certification special conditions when first adopted, and they require temperature monitoring to prevent thermal runaway.
EaglePicher has been making batteries since the 1920s and notes that most new battery technologies face the same adoption curve, starting with initial resistance and then acceptance. “Sometimes it’s hard to find a cutting-edge company willing to take an earlier risk,” Nowlin said. And as lithium-ion technology develops, work continues on finding reduced or non-flammable electrolytes, he added, “which would ease a lot of concerns.”
Two other business jets were slated for lithium-ion main-ship batteries and issued special conditions, the Spectrum Aeronautical S-40 (since canceled) and Gulfstream’s recently certified G650. “The G650 has lead-acid and Ni-Cad batteries,” a spokeswoman told AIN. “Early in the G650 program, Gulfstream did investigate using Li-Ion batteries. However, we made a change during the development program to today’s batteries.” The battery was being developed by Tucson, Ariz.-based Securaplane Technologies and used lithium-iron phosphate technology. Weight savings per shipset for the G650 were projected to equal the weight of one passenger.
Embraer’s Legacy 450/500 will be equipped with lithium-ion emergency batteries, according to a Securaplane statement issued in July 2010. Securaplane and Embraer declined to comment for this article.