ExxonMobil flexes R&D muscle in Anaheim

December 6, 2007

ExxonMobil Chemical showcased a new film technology platform for hybrid and electric vehicle batteries at the 23rd Electric Vehicle Symposium and Exposition (EVS-23) in Anaheim, Calif. on December 2-5, 2007.

ExxonMobil Chemical and ExxonMobil’s Japanese affiliate, Tonen Chemical, have developed new battery separator films that are expected to significantly enhance the power, safety and reliability of lithium-ion batteries used in hybrid and electric vehicles. As a result, the new film technologies have the potential to improve the energy efficiency and affordability of the next wave of lower-emission vehicles. Building off a new technology platform, ExxonMobil Chemical expects to capitalize on emerging market needs by providing tailored film grades to meet specific battery maker or original equipment manufacturer requirements.

The new battery separator films are produced using a proprietary wet, bi-orientation manufacturing process that results in fine, highly uniform pores. The films are co-extruded using specially tailored, high heat-resistant polymers. Relying on ExxonMobil Chemical’s technology and polymer experience, developers were able to fabricate films that exhibit enhanced permeability, higher meltdown temperature and melt integrity, while maintaining quick shutdown performance and mechanical strength. The higher meltdown temperature significantly increases the film’s thermal safety margin.

“One of our safety solutions improves the thermal mechanics of one of the battery’s most vital components—the separator,” says Jim P. Harris, senior vice president, ExxonMobil Chemical Company. “With what are essentially very thin, but critical layers of highly-engineered film, you can improve the battery’s safety performance and help make the next generation of hybrid and electric vehicles possible.”

Separator film is an integral part of battery system design and critical to overall performance, according to Harris. First announced in May 2007, the new Tonen film was introduced to the public this week for the first time. During operation of the battery, the film separator is porous, admitting lithium ions through. They can close, however, at high thermal events (about 130ºC) to isolate cell segments, protecting the entire battery system from thermal runaway events, which can trigger a meltdown or fire.

This is a pressing safety concern for lithium-ion batteries, which are desirable for automotive for a variety of reasons, including size-power ratios and charging cycles.

According to ExxonMobil Chemical scientists, further progress in this area of battery technology will require a more systems-oriented approach to guarantee safety.

The new separators are currently being tests in commercial vehicle pilot projects, according to company representatives, and their introduction in mass-produced passenger vehicles might occur as early as 2010.

ExxonMobil Chemical has been working with lithium-ion battery separators for the last 20 years, and Tonen, a Japanese-based company, supplied the technology to enable Sony to produce the first commercially-marketed lithium-ion batteries.

“These technologies are consistent with our long-standing commitment to improve energy efficiency,” says Harris. “We are investing resources to customize these new separator films to meet the specific lithium-ion battery system requirements and will continue to work with all manufacturers to speed the progress of next generation vehicles.”

SOURCES: ExxonMobil Chemical, Green Car Congress