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Intrinsically safe energy storage is an oxymoron. The objective is storing large amounts of energy to be released slowly over time - if there exists any possibility whatsoever of imperfect containment, there is (by definition) some probability that it will fail and release that energy all at once.

Can they be made to fail safely? Sure.

Can they be made to never fail? Not for what anyone's willing to pay for them.

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Lithium batteries store about 0.5 MJ/kg. Compared to the specific energy of burning lithium metal (40 MJ/kg) the energy from the electricity producing redox reaction is pretty low.

In the case of lithium batteries. Our problem isn't the stored electric energy, it's the medium being a highly flammable alkaline metal. If we could somehow store that 0.5 MJ/kg in a non-flammable medium with similar energy density it would have 5% the specific energy of a similarly massing piece of hardwood.

Oh damn, TIL. You'd still have the issue of the stored energy in a non-flammable medium, but that 80x energy multiplier makes the problem distinct from any other energy storage I can think of. That's like keeping your diesel in a tank made entirely out of dynamite.

A candle stick has 100x the energy of a stick of TNT. I know which one I would rather be driving a truck full of.

Energy density is not the main danger factor.

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