The batteries at the heart of the problem, manufactured by the Japanese firm GS Yuasa Corporation, are essentially giant versions of the lithium-ion batteries used in cell phones and laptops. Like those batteries, the Dreamliner's use a lithium-cobalt oxide cathode, which is "an inherently unsafe cathode," said Mark Allen, assistant professor of chemistry and biochemistry at the University of Maryland, Baltimore County. And in the larger form used by Boeing, they pose an even larger risk. When overcharged or damaged, they can become essentially a firebomb inside the airplane—one that burns without air and can't be put out by usual aircraft fire suppression systems.
I really never expected anyone to say that the problems in the electrical systems of the 787 might be due to the chemistry of batteries, but you'd think someone would have at least looked at the Wikipedia page:
Batteries produced with LiCoO2 cathodes, while providing good capacity, are more reactive and have poorer thermal stability than batteries produced with other cathode chemistries. This makes LiCoO2 batteries more susceptible to thermal runaway in cases of abuse such as high temperature operation or overcharging. At elevated temperatures, LiCoO2 decomposition generates oxygen, which then reacts exothermically with the organic materials in the cell. This may pose a safety concern due to the exceptional speed and magnitude of the highly-exothermic reaction, which can induce thermal runaway in adjacent cells or ignite nearby combustable materials.
Fascinating.