I think that the problem is that most lithium batteries use metal oxides (e.g. cobalt) which are inherently unstable and liable to thermal runaway.

There is an alternative: http://www.valence.com/saphion.asp but I guess that it is more costly.

Using phosphates instead of oxides would probably result in you needing a slightly larger and heavier battery, but there does seem to be a marked improvement in its working life.

There is a safety video on the valence site...........one of the tests is to shoot the battery!