Sodium batteries offer an alternative to tricky lithium

In the early 20th century Britain’s Royal Navy converted its ships to run on oil instead of coal. But whereas coal could be produced at home, oil had to be imported. That caused jitters: what if those imports were one day cut off? Winston Churchill, who was in charge of the navy at the time, argued that the best defence was a diversity of supply. As he told a fretful Parliament: “Safety and certainty in oil lie in variety and variety alone.”These days, politicians in rich countries find themselves in an even tighter bind. They need to switch not just their navies, but their entire economies from fossil fuels to low-carbon electricity to avert the worst consequences of climate change. But they worry that doing so will leave them geopolitically exposed.