I'm skeptical of their cost claims. Turbines aren't cheap and compared to batteries, they require significant maintenance. And while you can increase energy storage by increasing the size/number of CO2 tanks, the only way to increase power output (or "charging" speed) is to add more/bigger compressors and turbines.

There's also the issue of volumetric energy density. Wikipedia says that compressed CO2 storage has an energy density of 66.7 watt-hours per liter, though it's unclear if that's before or after turbine inefficiencies.[2] And that's the density in a compressed tank. It doesn't count the volume of the low pressure dome, which is many times larger. For comparison, lithium batteries are 250–700Wh per liter depending on the chemistry. Specific energy (energy per unit mass) is better than lithium ion, but since these are fixed installations, mass isn't a major concern.

Considering their claims are for a theoretical full scale plant, and that the numbers are already worse than batteries (75% efficiency, lower volumetric energy density, $200/kWh), I'm not optimistic. This technology might have niche uses, but I don't see it competing with most lithium battery installations.

That said, I hope I'm wrong. The more energy storage solutions we have, the better our future will be.

1. https://www.energy-storage.news/energy-dome-launches-4mwh-de...

2. https://en.wikipedia.org/wiki/Compressed_carbon_dioxide_ener...

It's sort of like arguing for going back to steam engines because we've got a new way to boil water.

The mechanical complexity is what worries me most - CO2 phase changes, compression/decompression cycles, heat exchangers...that's a lot of potential failure points compared to solid-state lithium cells. When researching portable power stations (I used gearscouts to compare $/Wh across different capacities), even budget lithium units are getting surprisingly cost-effective. We're seeing <$0.30/Wh for some models now.

That said, if Energy Dome can achieve reasonable $/kWh at grid scale without the lithium supply chain constraints, the efficiency trade-off might be worth it. The real question is whether the mechanical complexity translates to higher maintenance costs that eat into any capex savings.

https://gearscouts.com/power-stations

Heat-based energy storage is always going to be inefficient, since it's limited by the Carnot efficiency of turning heat back into electricity. It's always better to store energy mechanically (pumping water, lifting weights, compressing gas), since these are already low-entropy forms of energy, and aren't limited by Carnot's theorem.

I don't know much about this CO2 battery, but I'm guessing the liquid-gas transition occurs under favorable conditions (reasonable temperatures and pressures). The goal is to minimize the amount of heat involved in the process, since all heat is loss (even if they can re-capture it to some extent).

So, in a hot climate, they need to store it deep enough underground, and cool the liquid somehow below ambient temperature.

Um no, that's unfair. CO2 is an easy engineering choice here. It's easy to compress and decompress, easy to contain, non-flamable, non-corrosive, non-toxic and cheap. It's used in many applications for these reasons.

While CO2 is now a great evil among the laptop class, it has been a miracle substance in engineering for roughly 200 years now.

I wonder if something like the paraffin phase transition could be used to limit the temperature of the heat reservoir, and thus the losses during storage.

E.g. if they can use the waste heat for district heating and count that as useful work.

I worry the answering that question requires answering this question: whose negative externalities?

I am very interested in this question, but those who raise it never have answers about the negative impacts of mining lithium.

For example, the amount of lithium needed for an EV is an order of magnitude less than the amount of steel needed. What is so bad about lithium mining that it's 10x worse than iron mining, pound for pound?

Nobody has ever answered my request for environmental concerns with a concrete environmental lithium mining concern, such as acidification that can sometimes happen with iron mining.

I've researched and researched, found nothing, which leaves me thinking that the worst case scenario for lithium is no worse than the worst case for iron.

Meanwhile, we have such immense documented harms from fossil fuel extraction that nobody ever questions again, or with the same intensity that's reserved for supposedly toxic lithium batteries.

The apparent benefit is massive, so any delay seems to cause massive harm to the environment.

I think we need to flip the question: where is the proof that coal/oil/iron is better for the environment than mining and recycling batteries? (BTW, it's at least 20 years now for grid batteries, with lifetime going up all the time...)

If the processes to extract Lithium from recycling become cheap enough to compete with the prices of mined Lithium, then that happens.

Processes still need to be invented/scaled for that to happen: the only real way to deal with damaged or charged cells that I know of is to deep freeze them, shred them, and then defrost them slowly.

But in either case: Lithium is going to end up as waste. Making it cheaper to make cars affordable and the grid more stable means that disposable batteries will be even cheaper.

I don’t know how modern batteries fare in landfills: Most modern solar panels, for example, are relatively clean (mostly aluminum, silicon, copper, wee bits of lead). But not a waste management expert.