The news: One of the leading companies offering alternatives to lithium batteries for the grid has just received a nearly $400 million loan from the US Department of Energy. Eos Energy makes zinc-halide batteries, which the firm hopes could one day be used to store renewable energy at a lower cost than is possible with existing lithium-ion batteries. What they're made of: Eos's batteries are primarily made from zinc, the fourth most produced metal in the world, and use a water-based electrolyte (the liquid that moves charge around in a battery) instead of organic solvent. This makes them more stable than lithium-ion cells, and means they won't catch fire. Why it matters: While the cost of lithium-ion batteries has plummeted over the past decade, there's a growing need for even cheaper options.