Sodium, found all over the world as part of salt, sells for 1 to 3 percent of the price of lithium and is chemically very similar. Recent breakthroughs mean that sodium batteries can now be recharged daily for years, chipping away at a key advantage of lithium batteries. The energy capacity of sodium batteries has also increased.

Chinese battery executives said in interviews that they had figured out in the past year how to make sodium battery cells so similar to lithium ones that they can be made with the same equipment. The Chinese giant CATL, the world's largest manufacturer of electric car batteries, says it has discovered a way to use sodium cells and lithium cells in a single electric car's battery pack, combining the low cost and weather resistance of sodium cells with the extended range of lithium cells. The company says it is now prepared to mass-produce these mixed battery packs.