ExxonMobil Chemical: Update on Li-Ion Separator Film

4 December 2007

While attending EVS-23 in Anaheim, representatives of ExxonMobil Chemical and Tonen Specialty Separator Godo Kaisha talked up the merits of their new separator film for lithium-ion batteries. The new film was announced in May (earlier post), and features a built-in safety mechanism that is triggered by high temperature.

During normal operation, the separator in a lithium battery cell is porous to lithium ions. A thermal separator such as that produced by Tonen can close under high heat—typically 130ºC, and referred to as a “thermal event”—to isolate one part of a cell, reducing the potential for the event to cascade into thermal runaway.

“What we’re learning is that a battery is like a machine, and all the parts have to work together” said Andrew Malkin, president of Tonen Specialty Separator. “In the past, battery components were sort of tossed over the fence by suppliers, and the battery manufacturers would then give the components a pass or a fail.” Pat Brant, chief scientist for ExxonMobil Chemical, echoed that point, explaining that the drive for higher efficiency battery packs requires that all of a battery pack’s components be designed from a systematic point of view, even when sourced from different companies.

Such a task can be difficult, given the myriad of lithium-ion chemistries now under test, as well as the need for cell manufacturers to guard proprietary technology. Malkin and Brant both argued the need for a battery testing center that would conduct standardized tests, to help encourage standardized safety standards which would help the future EV and PHEV consumer make their buying choices.

Tonen’s separators are now being used in commercial vehicle pilot projects, said Malkin, and he expects to see his company’s separators used in mass-produced passenger vehicle applications “by 2010.”

Tonen Specialty Separator Godo Kaisha, an ExxonMobil affiliate, is part of TonenGeneral Sekiyu K.K., which is headquartered in Tokyo, Japan. The company produced the world’s first lithium-ion battery separator in 1991 for Sony, which itself produced the first commercial lithium-ion batteries. Affiliates of Exxonmobil collectively hold a majority of TonenGeneral stock.