From Musk interview with Bloomberg:
“Musk has previously complained about the availability of battery metals like lithium and nickel, pushed commodities companies to lift supply, and discussed the prospects for Tesla to become a miner itself — a step already being taken by some other EV and battery producers.
”We just think about how do we address the limiting factors in the supply chain and in our own industrial capacity,” Musk said. “Basically, we need to build the factories faster, and then we need to look ahead to whatever the choke points are in the whole lithium-ion battery supply chain, from mining and refining to cathode and anode production and cell formation”