It has been discussed a few times, in particular
https://news.ycombinator.com/item?id=48171906 (57 points | 5 days ago | 46 comments)
> Energy density is 1.65 MJ/kg, beating lithium-ion (~0.9 MJ/kg)
Lithium-ion produce electricity, that can be used by a heat pump to get a greater than 100% efficiency measured in heat/electricity. Heat pumps have like 300% of efficiency, sometimes more, but let's assume only a 200%. In that cases
this molecule -> 1.65 MJ/kg (heat)
lithium-ion -> 0.9 MJ/kg (electricity) -> 1.8 MJ/kg (heat)