Most of today's batteries are made up of rare lithium mined from the mountains of South America. If the world depletes this source, then battery production could stagnate. Sodium is a very cheap and earth-abundant alternative to using lithium-ion batteries that is also known to turn purple and combust if exposed to water—even just water in the air. Worldwide efforts to make sodium-ion batteries just as functional as lithium-ion batteries have long since controlled sodium's tendency to explode, but not yet resolved how to prevent sodium-ions from "getting lost" during the first few times a battery charges and discharges. Now,...