Elon Musk signed a deal last month with Australia’s Syrah Resources, which operates one of the world’s largest graphite mines in the South African country. It’s a unique partnership between an electric car manufacturer and a base metal producer for lithium-ion batteries. The value of the business was not disclosed. Tesla will purchase the material from the company’s processing plant in Vidalia, Louisiana, which makes graphite from its mine in Balama, Mozambique. The Austin, Texas-based electric car maker plans to buy 80% of the plant’s output — 8,000 tons of graphite annually — by 2025, according to the understanding. Syrah...