This is a good development, but it falls really short of the almost 3.5 kWh that would be possible to achieve with sodium metal fuel cell. Such device is described in the expired patent US3730776A (copy available here: https://orgpad.com/file/DrCoHGH6xJJqraDeusqrtS?token=D6S5Bow...)
A similar device producing electrical current can be constructed in a garage.
The point is not energy density, or momentary power. The point is low price and immediate availability.
There is a lot of solar and wind electricity wasted in the world because there's no economical way to store it. LiFePO4 batteries are > $100 / kWh, last time I checked; a practical powerwall costs like a small car, and is also a major fire hazard.
We badly need cheap, non-toxic, non-flammable batteries we could deploy massively outside of cars, drones, and phones. The announced battery looks like something that may fit the bill.
If you want to store a lot of energy cheaply, the density (and power per volume/ area) is a killer property. The Castner process to electrolytically convert NaOH to sodium metal is known and was deployed at industrial scale even 100 years ago. The other direction, where you get energy by reacting sodium metal with water is described in the patent, which was reproduced successfully in a garage/ home workshop setting. It obviously worked for Lockheed.
Btw. sodium has many desirable properties even in the metal form. You can store it quite efficiently on pallets probably just wrapped in some foil. You would be able to store more than 3 MWh on a single pallet. No battery can match that. It's more like a replacement for stationary diesel generators - but you can recycle the resulting sodium hydroxide solution back to sodium using renewable energy quite easily.
Also sodium reacts with water so readily you could probably get stable current with just ~50 ms of delay, which on the grid would still be considered instantaneous. You don't need any expensive catalysts, spark plugs, pressure nothing. Just a thin film of water on a metal plate and some sodium to push against it.
My point is that a battery half as space-efficient as a lithium battery, and even 10 times heavier per kWh stored, may still be great for storage if its cost is, say, 20% of the lithium-based battery, and it's not flammable.
You can put these huge batteries under your solar arrays and your wind turbines, on the land already paid for. If it's not flammable, you can hide it in a basement.
The sodium extraction process is cool! Metallic sodium is highly flammable though.
A battery is something entirely different than a fuel cell. A fuel cell decouples capacity, power, discharging and charging, which is usually done by a different apparatus/ machine. A fuel cell is more interesting for longer applications, where you would build diesel generators, "peaker" power plants, seasonal energy storage. (E.g. you would produce a lot of sodium in the summer and react it to sodium hydroxide in the winter. In the summer you would recycle it back to sodium to store energy for the winter.) It should btw. be possible to transport sodium using very similar ships that nowadays transport crude oil. You could also transport sodium on pallets in colder climates as it is solid < 100˚C.
