Apple introduced the iPhone Duo on Sept. 9, marking its first foldable iPhone. The device starts at $1,999 in the U.S. and opens to a 7.6-inch inner display. When closed, it uses a 5.4-inch outer screen for standard phone tasks.

The United States is expanding domestic battery production as it works to reduce dependence on China. The larger challenge sits deeper in the supply chain. China still dominates battery materials, processing and key manufacturing technologies used worldwide. U.S. factories have