Few technologies excite me more than grid-scale liquid metal batteries. They're not as fully developed as other green technologies such as plug-in vehicles, wind turbines and solar panels, but they have the potential to have a gigantic impact on our civilization and, in turn, on its impact on our planet's ecosystems. By allowing us to potentially store large quantities of energy cheaply and robustly (no need to worry about power spikes, temperature variations, etc), they could make a transition to renewable energy much faster and easier. For more details, see the TED talk at the bottom of this post or check out this older post.
Technology Review has a profile that you should read from start to finish, but here's an excerpt if you're in a hurry:
Ambri cofounder Donald Sadoway, a professor of materials chemistry at MIT, conceived of the liquid-metal cell as a way to build a grid battery that could store many hours’ worth of energy from solar and wind power at very low cost. Because a stationary battery intended to store power for the grid wouldn’t have to be lightweight like the batteries in our laptops, cars, and flashlights, he was free to depart dramatically from the chemistry that powers those devices. The result is a battery that’s made from abundant, inexpensive materials in a simple production process. It can safely handle large currents and deliver power in quick bursts or for an extended period. [...]
When Sadoway first considered grid storage in 2005, he looked to aluminum smelters for inspiration. These massive machines, which can stretch to more than 200,000 square feet, use huge amounts of electricity to extract aluminum from molten aluminum oxide through electrolysis. Sadoway, who is trained as a metallurgist, realized that smelting could provide a template for a rechargeable battery that tolerates the current levels needed for the grid. “I looked at that and said, Wow, that looks like half of a battery! And it’s big, it’s scalable, and it’s cheap,” he says.
After hitting upon the idea of the liquid-metal battery, Sadoway searched for the perfect electrodes: he ended up choosing magnesium and antimony because they are cheap and separate naturally when in liquid form, the lighter magnesium rising to the top. A liquid-salt electrolyte rests between the magnesium and antimony electrodes, creating a cell with three layers.
But really, read the whole thing, or at least check out the TED video below.