Why did it take until now to get to lithium batteries? Why way NiCad the thing before? Will lithium continue to dominate, or are there other competitive solutions just one breakthrough away? What about hydrogen cells?
Hydrogen is not a solid or a liquid at room temperature and is also too volumetrically in-dense.
A bucket of gasoline contains more hydrogen atoms than a bucket of liquid hydrogen, it contains more chemical energy, and you can actually keep it in a bucket at room temperature without anything terrible happening.
Sure, liquid hydrogen has a lot of energy by weight, but energy storage needs to be good by weight and by volume, and hydrogen is terrible by volume.
There are cases for using hydrogen as your energy storage, but if your thing is smaller than a truck, it's probably not one of them. There's just so much wishful thinking around.
Pretty much everything else about it is bad. Shame.
So hydrogen electrolysis would be the root of renewable chemistry just like fossil hydrocarbon is the root of almost all current chemistry (where even processes that use hydrogen are sourcing that from fossil hydrocarbons). You can have a "hydrogen based economy" even without any meaningful amount of H2 ever stored or leaving the power-to-x plant.
Usage site H2 applications are a dead-end, that's something I would have signed ever since the "hydrogen economy" proposed by George W. Bush (funny how benign hindsight looks at him post-Trump). Admittedly, back then I was also completely unaware that "hydrogen based economy" wouldn't necessarily mean "H2 to the home", I was just shooting down that idea with basically the same inevitability arguments as yours.
Again, speaking from my lived experience, NiCd pushed to the limit resulted in many gnarly fires in high performance RC use, NiMh was never a contender given low output (again low discharge rates). LiPo is king here, both in terms of output and weight/power, but overcharging or excessive discharging results in thermal runaway. Lithium ion is far safer, but less effective.
So I think yet another benefit of lithium is also that it's relatively easier to deal with over its whole life cycle. Elemental lithium is of course quite reactive, don't want to be directly exposed to it, but it doesn't stay that way in nature. That it's extremely abundant and distributed doesn't hurt either. While for economic reasons it makes sense to get it initial from naturally highly concentrated sources, and to recycle lithium packs, it'd be perfectly viable to pull it right out of the ocean with solar power if there was ever a need.
A NiCd cell has 1.2V per cell, a lithium cell has 3.2-3.7V per cell, so they need to have three times the electron density just to break even. They are about 1.5-2.0x higher IIRC and aren't getting better, while we are still improving lithium slowly.