Re: You can never have too much Lithium
@Adair: That's an entirely reasonable assumption. But I think it's somewhat flawed. For example, metal-air (Zinc-air, Aluminum-air) have significantly higher energy densities than Lithium-ion and aren't (anywhere near as) subject to thermal runaway. So why are we messing around with Lion? Simple. Currently practical metal-air batteries are primary cells -- not rechargeable. Pretty much restricted to hearing aids and a few similar applications. Lion OTOH is not only rechargeable, if not abused, it can be recharged a lot of times before performance degrades significantly.
Choice of battery chemistries involves juggling a bunch of considerations. Energy density, temperature range, self-discharge rate, tendency toward thermal runaway, outgassing, toxicity, number of recharges, etc, etc, etc.
I'm not an expert on batteries. Probably others around here know much more than I and might tell us more.
FWIW, my impression is that the holy grail of transportation batteries would be a metal-air battery (possibly Aluminum-air?) with mass, range, safety parameters comparable to fossil fuel. The vision is that you'll haul into a service station, make use of the facilities, buy an overpriced snack, pull out your old degraded Aluminum anodes, throw them in a recycle bin, insert new ones, and be on your way. "They" have been working on that for 40 years. They can't even run a demo today. ... Maybe in another 40 years. ... Maybe never.