There's also someone building a factory to make iron-air batteries for grid storage. They're way cheaper than lithium or even sodium, with one of the most common materials on the planet, but only about 50% efficient. They're too heavy for vehicles, and have lower power output so aren't much good as peakers, but if you want four days of grid backup like we'd need with a 100% wind/solar grid, they're great.

https://formenergy.com/technology/battery-technology/