The U.S. is turning to a much-criticized source as it races to secure supplies of battery metals to meet the growing demand for electric vehicles. To do so, it is homing in on cobalt from the Democratic Republic of Congo’s informal mining sector, where miners, sometimes including children, often work with no safety equipment in dangerous, hand-dug mines. Congo supplies around 70% of the world’s cobalt, a key metal in the lithium-ion batteries used in EVs, with about a third of that coming from these so-called artisanal miners. The U.S. Agency for International Development said earlier this year that it...