That's very interesting. If they can be used at home or in cars that don't require batteries with a very large capacity, then that would be really good to counter the scarcity of lithium (and hopefully, help the environment too)

If they can get industrial scale it could also allow energy grids to capture excess power instead of wasting it. Could yield massive efficiency increases being able to reclaim some of that loss.

Instead of thinking "capacity" by itself, thing of "capacity for the given space" or rather "density". So Sodium batteries can be equal capacity as Lithium, but the equivalent capacity Sodium battery will be significantly larger. In applications like storing overproduced wind or solar electricity for use later, we don't care how big the battery is. However, it a moving vehicle where every square centimeter and every kg changes the performance of the car, those density differences can have a real impact.