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Comment by foobarian | Hacker News Reader

For comparison gasoline has about 9000 Wh/L of raw chemical energy, of which maybe 30-40% gets converted to useful work.

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https://en.wikipedia.org/wiki/Energy_density

Gunpowder is 4-10 times less energy dense than gasoline. The difference is that gunpowder includes fuel and oxygen-producing substances, much like most of Li-ion batteries.

This thing is in gunpowder energy density range.

ICE engines outsource half of the reactants to the atmosphere, so this comparison isn't as useful as it appears at first.

Batteries can make use of the atmosphere as well (eg aluminum air batteries/ or venting hydrogen in lead acid batteries) although I don’t know of any rechargeable chemistries off hand that use environmental oxygen. All that to say the trick is available for batteries even if the best current chemistries by mass density don’t make use of it.

One I'm familiar with (but don't know deeply about) is Iron-air batteries [1]. Form Energy [2], an interesting grid-storage startup uses them. They're not energy-dense whatsoever, but very cheap, which makes them economical for that application.

[1]: https://en.wikipedia.org/wiki/Metal%E2%80%93air_electrochemi...

[2]: https://formenergy.com/technology/battery-technology/

30…40% is very ideal number, 15…25% is often the reality.

A good hybrid can do very well. Presumably by keeping the engine in exactly its sweet spot and designing aggressively for that. BYD for example claims 46% thermal efficiency. [0]

[0] https://ev.com/news/byd-hybrid-efficiency

Yes, hybrids are much more efficient especially in city driving, not so much on highway. I used to drive a Prius back in the day.

Almost half way there

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