Today, lithium-ion batteries are the default choice to store energy in devices from laptops to electric vehicles. The cost of these kinds of batteries has plummeted over the past decade, but there’s a growing need for even cheaper options. Solar panels and wind turbines only produce energy intermittently, and to keep an electrical grid powered by these renewable sources humming around the clock, grid operators need ways to store that energy until it is needed. The US grid alone may need between 225 and 460 gigawatts of long-duration energy storage capacity by 2050.

New batteries, like the zinc-based technology Eos hopes to commercialize, could store electricity for hours or even days at low cost. These and other alternative storage systems could be key to building a consistent supply of electricity for the grid and cutting the climate impacts of power generation around the world.

In Eos’s batteries, the cathode is not made from the familiar mixture of lithium and other metals. Instead, the primary ingredient is zinc, which ranks as the fourth most produced metal in the world.

Zinc-based batteries aren’t a new invention—researchers at Exxon patented zinc-bromine flow batteries in the 1970s—but Eos has developed and altered the technology over the last decade.

Zinc-halide batteries have a few potential benefits over lithium-ion options, says Francis Richey, vice president of research and development at Eos. “It’s a fundamentally different way to design a battery, really, from the ground up,” he says.

Eos’s batteries use a water-based electrolyte (the liquid that moves charge around in a battery) instead of organic solvent, which makes them more stable and means they won’t catch fire, Richey says. The company’s batteries are also designed to have a longer lifetime than lithium-ion cells—about 20 years as opposed to 10 to 15—and don’t require as many safety measures, like active temperature control.

There are some technical challenges that zinc-based and other alternative batteries will need to overcome to make it to the grid, says Kara Rodby, technical principal at Volta Energy Technologies, a venture capital firm focused on energy storage technology. Zinc batteries have a relatively low efficiency—meaning more energy will be lost during charging and discharging than happens in lithium-ion cells. Zinc-halide batteries can also fall victim to unwanted chemical reactions that may shorten the batteries’ lifetime if they’re not managed.