If fusion power pans out, and there are signs that it will, the world will need a lot more lithium.

That’s the bet behind Licube, a startup that has licensed technology from Hirosaki University in Japan, to purify lithium-6, the form of lithium that fusion plants need to make their own fuel, out of naturally occurring lithium.

The reason comes down to the fuel supply. A lot of things have to go right for fusion power to hit the grid, and one of them is the fuel. Most planned plants would run on a mix of two fuels, deuterium and tritium. Deuterium is easy to come by, but tritium is extremely rare in nature, and it’s an open secret in the fusion world that there isn’t enough of it to power every planned plant.

The proposed workaround is to make tritium on site, inside the power plant itself. A fusion reaction gives off a stream of fast-moving particles called neutrons. Startups plan to surround the reactor with a blanket of lithium, so that when a neutron strikes a lithium atom, the atom splits into helium and tritium. The tritium can then be collected, purified, and fed back into the reactor as fuel.

Not all lithium does this job equally well. It comes in two slightly different forms, lithium-6 and lithium-7, named for their weights. 5% of natural lithium, and the rest is the heavier lithium-7. Separating the two is difficult, and there is little capacity to do it today, so the world doesn’t have enough lithium-6 either.

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