The periodic table is limited. Of all metals, lithium is the lightest. It also has the highest mass-specific conductivity and the highest chemical specific energy of all the metals.

Hydrogen is not a solid or a liquid at room temperature and is also too volumetrically in-dense.

I have never really understood the hydrogen hype train, because liquid hydrogen is terrible in so many ways.

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.

You are absolutely right. The great appeal of hydrogen is that you can get it straightforwardly from water and it oxidizes back to water. Hard to imagine a cleaner energy cycle, subject to the extraction energy source but that’s in common with the alternatives.

Pretty much everything else about it is bad. Shame.

Hydrogen storage becomes quite easy when you forget about H2 for a while and focus on the energy content instead. Add some other atoms into the mix and you get something much more benign with little energy loss. Methane (CH4) is the obvious first candidate because it's so close to what we are used to burn, but ammonium (NH4) is also a good "storage hydrogen" (this one you'd want to split before burning, but it's easier to make because there's far more N than C in the air). Ammonium liquefies at easily achievable -33C or at room temperature under pressures no higher than what you find in certain bicycle tires. Some are even exploring the viability of iron dust as an energy storage medium: it oxidizes quite violently and would be recycled from the resulting iron oxide dust with hydrogen.

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.

NiCd is actually more capable than NiMh, but suffers from memory issues (capacity decreases significantly if not carefully discharged and recharged; ie you cannot “top them off” without sacrificing capacity.

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.

As a non-performance (including weight) practical matter as well, cadmium is just plain a rather toxic heavy metal. IIRC the EU has outright banned NiCd batteries entirely with a few very minimal legacy exceptions (medical devices I think?). Even though in principle part of the price is supposed to cover proper disposal EOL, people being people plenty got tossed and it's nasty stuff to have in a landfill even let alone elsewhere. There isn't any real treatment for it either as far as I know, normal heavy metal treatments like chelation therapy don't really work with Cd.

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.

LiPo is a type of Li-ion battery and they have much the same safety characteristics. Lithium iron phosphate (LiFePO4) batteries are much safer, they don't tend to run away.

What about lithium and memory? Do lithium batteries have big memory issues, or is all the stuff rattling around in my head about batteries having memories mostly because I grew up when NiCd and NiMh were all the rage?

If you grew up with both you must remember how NiMH was initially championed as "no memory effect". It was still there, but so weak compared to NiCd that the claim wasn't really disputed. Lithium are at least another step of that size better than that, if they have memory effect at all. If they do have a tiny little memory effect left it's probably smaller than the extra cell aging one deep cycle would cause compared to to two smaller cycles of the same total capacity, as least as long as the smaller cycles are taking place somewhat close to nominal voltage. That would at least make memory effect irrelevant for all practical purposes.

Lithium doesn’t have any memory effect.

Asimov promised me miniaturized nuclear batteries. Sad face.

They were supposed to fit in a belt buckle!

Hydrogen cells will always have 10x+ the inefficiency of a lithium battery. They will always be niche for cost reasons.

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.