Lithium-ion batteries are on the move. Popular for many years in consumer electronics, these battery packs, notable for high energy density, low rates of self-discharge and low levels of maintenance, are increasingly used in electric vehicles, military applications, and aviation and aerospace design. Jean-Marc Thevenoud, marketing manager at French battery designer and manufacturer Saft, says it will take time for lithium-ion technology to make serious inroads into aerospace: “For any new technology on the market, it is in a learning phase. But step-by-step, people are using more and more lithium ion because of weight-saving and maintenance advantages.”
In fact, there have been widespread concerns over the safety of lithium-ion batteries when used in aircraft systems—or even when lithium-based batteries are transported by aircraft. UPS Airlines Flight 6, a cargo flight operated by UPS Airlines flying between Dubai and Cologne, Germany, crashed following an inflight fire in September 2010, killing its two crew. The fire was subsequently found to have begun in the contents of a cargo pallet containing more than 81,000 nonrechargeable lithium batteries—leading the FAA to issue restrictions on carrying them in bulk on passenger flights.
Then, over the course of a year of the newly launched Boeing 787’s operation (2013-14), a series of incidents occurred highlighting problems with lithium-ion batteries used in the new aircraft’s systems. They began with a fire that started in a battery that overheated in an empty 787 operated by Japan Airways (JAL) at Boston’s Logan Airport in January 2013, followed a few days later by a battery malfunction onboard an All Nippon Airways (ANA) 787 that forced the aircraft into an emergency landing.
A year later, in January 2014, a JAL maintenance crew at Tokyo’s Narita International Airport discovered smoke coming from the main battery of a new 787. This was soon followed by another incident, in which a lithium-ion battery onboard another JAL 787 emitted smoke and partially melted while the aircraft was undergoing maintenance.
The initial 787 incidents prompted ANA and JAL to ground their fleets in early 2013. The FAA soon ordered all U.S. operators to ground their 787s while an investigation took place; other airlines and countries opted to as well. The aircraft returned to the skies a few months later, but the reputation of Boeing—and lithium-ion batteries as a technology—had been dealt a blow.
Standards and Improvements
Indeed, aviation regulators have tightened the rules around the use and transport of lithium-ion batteries in recent years. But high energy density and low weight will continue to make them attractive to aircraft manufacturers trying cut fuel consumption. And a much lower rate of self-discharge than other rechargeable cells will no doubt see the batteries continue to be developed for aviation applications. But the International Civil Aviation Organization (ICAO) amended its rules on carrying lithium-ion batteries in the holds of passenger aircraft following the 787 incidents. ICAO is also now pursuing new guidelines around the transport of lithium-ion batteries within the cabin—such as in consumer electronics devices—as well as in the holds, says Anthony Philbin, ICAO communications chief.
The European Aviation Safety Agency (EASA) says that “lithium-ion batteries in general are significantly more susceptible to internal failures” such as overcharging and over-discharging, and that some feature flammable electrolytes. EASA issued a Certification Review in 2011 with strictures on maintaining safe lithium-ion cell temperatures and pressures, as well as ensuring that batteries were subject to flammable-fluid protection rules. It also requires that they incorporate fail-safe systems with the means to automatically disconnect the battery from its charging source in the event of failure and include monitoring and warning systems that would alert crew if batteries fall below the charge level necessary to power aircraft systems.
“For large aircraft, standards are currently being discussed with experts and standardization bodies, such as the RTCA, for different sizes of lithium-ion batteries,” explains Dominique Fouda, EASA head of communication and quality.
Air France Industries-KLM Engineering and Maintenance (AFI-KLM E&M) maintains various aircraft battery systems. Robert van Kesteren, manager of avionics engineering, says that “special challenges are related to the type of battery used on the aircraft. The new lithium-ion batteries represent different challenges than traditional nickel-cadmium (NiCad) batteries.” AFI-KLM E&M services 787 lithium-ion batteries as well as other types of battery systems.
Van Kesteren says battery vendor Thales has improved the 787 lithium-ion battery in a number of ways. “The previous model is no longer used. Also, Boeing has improved the 787 battery installation—and maintenance and operational procedures,” he notes. The component maintenance manual for overhauling 787 lithium-ion batteries has been updated to reflect modifications made to the 787 lithium-ion battery design, which include a sealed steel box around the battery and improved separation between battery cells. Boeing has introduced ceramic-plated spacers between them to cut risk of heat propagation, for example.
The AFI-KLM E&M shop in Amsterdam includes capabilities to service the lithium-ion battery used for the 787 main battery and auxiliary power unit (APU). On the 787, the batteries also are used for the flight data recorder remote independent power supply, wireless emergency lighting system, flight control electronics and emergency locator beacon. AFI-KLM is currently outsourcing repair of these other battery systems while it develops in-house capabilities to service them. “The batteries do not enter the shop very frequently—yet,” says Van Kesteren. He cites one incident in which a lithium-ion battery failed due to overdischarge—requiring complete replacement of the battery cell package.
Leaving their inflight use aside, storage and transportation of lithium-ion batteries continues to pose challenges. For example, 787 lithium-ion batteries are stored in a charged state because undercharged batteries pose a risk. This means they are charged at either 25% for regular storage, or at 100% for mission-ready batteries, which require specific checks on voltage and capacity to be carried out at a 6-12-month frequency. Regulations from the International Air Transport Association prohibit the shipping of failed lithium-ion batteries and cells by air. “This means that the battery is transported by truck when possible,” Van Kesteren says.
French battery-maker Saft says concerns over lithium-ion batteries should be allayed as further advances are made with cell technology. Saft has worked on lithium-ion systems for aerospace for 15 years and provides lithium-ion batteries for the F-35 Joint Strike Fighter, which features two Saft batteries. It has also been providing lithium-ion battery technologies for the Airbus A350 for 1.5 years. On the A350, Saft batteries are used to start the APU. They also provide the minimum level of back-up energy in an emergency. If there is an engine flame-out or loss of main electrical power, the batteries can supply vital functions such as avionics and radio to the network.
There is a long list of requirements that Saft batteries must fulfill to meet the demands of an OEM—including fire testing, liability and electrical testing. There is also a complex regime with many hundreds of testing cycles. “There is a lot of testing to be done to ensure we comply with requirements,” says Thevenoud. The company works closely with OEMs to develop new batteries to OEM specifications, and also helps the OEM develop those specifications, he says: “We design the best battery through a process of collaboration . . . because we know we will work with the OEM over the lifetime of the aircraft, which will be at least 20 years. It is a long-term partnership.”
Developing batteries with enhanced characteristics for maintenance is one aim. Saft already has refined a range of NiCad ultra-low-maintenance (ULM) aviation batteries featuring plastic-bonded technology and reduced water consumption, which increases the battery’s flight duration between maintenance stops. This Saft ULM battery may increase time between maintenance stops by more than 50%, the company contends. On the Airbus A330, Saft batteries have seen maintenance intervals of 1,000 operating hours rise to 3,000. This has significantly reduced operating costs. The lifetime of the battery is also longer, reducing total cost of ownership.
On the A350, the four lithium-ion batteries save the weight of one passenger: 80 kg (176 lb.). “This is very significant for an aircraft,” says Thevenoud. The second advantage is an improved maintenance interval for lithium-ion, which is increased to two years. This compares to 3-6 months for a NiCad battery. Changes to batteries also can be made “on-wing” using Saft ground support equipment. Batteries can be tested while on the aircraft, speeding up maintenance checks and cutting time and cost for aircraft operators.
Air France-KLM E&M says it is developing capabilities to maintain the lithium-ion batteries on the A350.
Thevenoud says the battery system developed by Saft for the A350 is the first lithium-ion battery in the world that is compliant to Design Assurance Level (DLA) A, the highest achievable DLA on an aircraft. He concludes: “People should not worry about lithium ion. If the chemistry is well-controlled and the company making the batteries controls the process correctly, it is fine.
“We have been working with Airbus for a long time to make sure the batteries are safe.”