Li-Ion Battery Bloat: Moisture the Culprit

Soon after reading my editorial on a pregnant iPod, DN reader Richard Sheryll came across his old Palm m500 in a pile of discarded devices. The front casing was ripped off,” he wrote, “and the lithium ion battery looked just as bloated as the one in your article.”

Glenn Gauvin had a similar experience recently when he went to swap out the battery in his 17-inch MacBook Pro. Digging into his briefcase, he pulled out the battery shown above–with a newly acquired paunch. “My bag was not mishandled, mistreated, or exposed to extreme heat or cold and it was less than a year old,” wrote Gauvin. “The guys at the Apple Store replaced it without question and would not answer my questions. Hmm!”

“It looks like these were cases in which the hermetic packaging was breached somehow and moisture got in,” says Don Sadoway, a professor of Materials Chemistry at MIT and an expert in advanced battery technologies.

Today’s thin-type lithium ion batteries employ a flexible, pouch-style foil housing, and Sadoway speculates that the material may have become brittle or possibly something cracked. Whatever the cause, the housing was compromised.

When moisture penetrates the inside of a lithium ion battery, that’s a problem, says Sadoway. “The lithium salts that are used in the electrolyte will become destabilized. Essentially, they react with moisture and generate hydrogen fluoride, which causes the cell to begin gassing and the battery to bloat up.”

In fact, Sadoway says, he has a research staffer who worked at a battery maker for 4 years. “They took the pains to inject with a syringe controlled amounts of water into flat pack batteries (some people call these ‘pouch cells’) to demonstrate that when water gets in, bloating occurs,” says Sadoway.

Taken to the extreme, the battery may rupture and the liquid inside ooze out, forming the kind of crusty residue most of us have discovered inside of a long-lost flashlight with regular zinc alkaline batteries inside.

Sadoway’s research at MIT is concentrated on alternatives to the electrolytes used in today’s lithium ion batteries. Given the technology’s sometimes finicky nature, as demonstrated here, he would love to see more people involved in this effort. “The electrolyte is the common element in these problems we see with lithium ion batteries,” he says, “and yet there isn’t much interest in doing anything about it.”