Battery safety starts in the factory

  • 08-May-2013 01:42 EDT
Saft 06.jpg

Saft's 270-V Li-ion battery on the Joint Strike Fighter provides start-up power for the auxiliary power unit and back-up power to operate the flight control surfaces during taxi, takeoff, flight, and landing.

The lack of standards directly targeted at the manufacturing of batteries for transportation applications does not mean the energy-storage devices cannot be made in a way that ensures their safe functioning.

That was one of the messages from battery maker Saft, a representative of which made a presentation at an April National Transportation Safety Board (NTSB) forum called “Lithium Ion Batteries in Transportation.” The NTSB conducted the forum during the period it was investigating a lithium-ion battery fire on a Boeing 787, but the forum was held for educational purposes and did not specifically address the Boeing incident.

Among the 18 presenters at the forum was Glen Bowling, Vice President of Sales, Saft Specialty Battery Group. The NTSB had asked Saft to report on standards that address quality control in the manufacturing of batteries. The company identified 28 standards that address batteries, Blowing said. “Unfortunately, none of them are specifically focused on manufacturing. In some cases they are addressing pieces of manufacturing, but not focused.”

And there are standards that address manufacturing quality control, but not batteries in specific, said Bowling, calling out as examples ISO 9001, AS 9100, “and I’m sure many more.” Those standards “provide a factory with a methodology…that is very complex, very complete, and it is a certified process. Depending on what organizations you work with, you will be asked to have this type of quality standard built in, and you’ll have a complete program to do it. And they do work well.”

A standard for cell and battery manufacturing is not practical because there are too many ways of making them, Bowling opined. If it ever got to the point of standardization, “it will be a very big book. And it will be different for every single [process], so it is not really going to be a standard,” he said.

“Depending on what you are making,” Bowling continued, “you will use different approaches. The very large mass-production manufacturers who are making a million cells a day use a completely different process to make their batteries than the people making the large cells—like Quallion, Saft, and some others…and so [the large producers] can’t check every one of those million every day. And they don’t. When we make a larger cell, we believe it is essential to check every single cell, so we use process and quality controls to control that.”

Among other things, Saft is very strict in specifying the exact contents of the materials it purchases for cell production. The company allows the suppliers to do most of the “checking” to ensure the materials meet Saft’s specifications, though it requires them to submit certification of impurity testing, according to Bowling. “We have fired suppliers,” he said. “It does happen.”

To ensure the initial purity of the material coming into the plant, Saft uses Class 6 dry and clean rooms in cell production. Workers are not allowed to touch the product in processes during which contamination is possible. Cells are checked for contamination at several points, including during final formation. There is a “very high probability” that the formation process will detect contamination, if present.

But even if missed during formation, contamination is detected during validation, in which every cell is tested. “I know that [testing every cell] is not true of everybody in the business, but we do,” said Bowling. The cells are validated to regulations and to customer standards.

“One-hundred percent of our cells go through multiple electrical tests—capacity for sure. Most of our cells are checked for impedance, and there are some other tests that I don’t want to mention here.”

Saft also conducts tests of modules and full batteries. “The battery is where the complexity comes in,” said Bowling. “We make everything from very small packages that may go on a Mar’s Lander to deploy something and everything up to very large satellite batteries that are going to space and staying there for 22 years. Each of those batteries has its own test program. Some of those test programs can last weeks and weeks and weeks, and some…can be done in three or four hours. But every battery, when it’s done, has a paper trail and a large book. That book covers everything that was done for that battery.”

The upfront, multi-year process of development, qualification testing, and safety testing to get to the point of being able to manufacture the product “is as important in guaranteeing the quality as what you do later on when you’re building that product,” Bowling concluded in his presentation.

In a subsequent question/answer period, he noted that Li-ion batteries are being used in an ever greater number of applications because the technology has matured enough to allow it. “The growth in the mission of Li-ion batteries is substantial,” said Bowling. “We are powering an airplane, the Joint Strike Fighter—doing something that has never been done before, because it can be done now … It’s a stretching of the technology boundaries, and we have to be professional when we do that.”

Aerospace Engineering asked the manufacturer of the Joint Strike Fighter, Lockheed Martin, how the batteries have performed to date. Its response via email: “The F-35 uses lithium-ion batteries manufactured by multiple suppliers. None of the F-35 lithium-ion batteries are from the same supplier as those used in the Boeing 787. The batteries used on the F-35 have undergone rigorous testing by industry experts and are safety-of-flight certified. To date, there have been no safety-of-flight issues associated with F-35 batteries. The batteries used on the F-35s have been through extensive tests and have redundant systems to protect the aircraft and battery compartments; they are safe.”

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