The cells in the 787, from Japanese company GS Yuasa, use a cobalt oxide (CoO2) chemistry, just as mobile-phone and laptop batteries do.
That chemistry has the highest energy content, but it is also the most susceptible to overheating that can produce “thermal events” (which is to say, fires).
Only one electric car has been built in volume using CoO2 cells, and that’s the Tesla Roadster. Only 2,500 of those cars will ever exist.
The Chevrolet Volt range-extended electric car, on the other hand, uses LG Chem prismatic cells
with manganese spinel (LiMn2O4) cathodes.