According to this article by the Wall Street Journal, Exxon is pretty serious about developing a new battery to work in electric and electric-gas hybrid cars. Lithium-ion batteries are notorious for getting too hot and catching on fire, but that hasn't stopped Exxon from employing "14 Ph.D.s in Japan, New Jersey and Texas" to improve the technology. In addition to that, according to the article, Exxon is also building a $300 million manufacturing facility in South Korea.
A quick examination of the lithium-ion wikipedia page makes me wonder if this is such a great thing after all. It seems as though there are several serious disadvantages and only a couple advantages. Who cares if the self-discharge rate is low if the battery charge capacity shrinks over time? Hopefully the 14 PhDs can fix some of that since I'd like to afford a hybrid some day.
According to the article Exxon won't make the actual batteries, but this isn't a huge leap for Exxon. Its scientists have already developed a "separator" film that is already an important part of lithium-ion batteries. That film is made of plastic, but guess what plastic is made out of?