How does cross-border ownership shape the lithium supply chain? Using global data on mines and refineries, I estimate a model in which ownership can lower refiners' effective ore costs, encourage mines to restrict spot sales, and soften competition. To study these effects, I examine policies motivated by national security concerns about reliable access to critical mineral inputs: divestiture of Chinese stakes in overseas producers and a ban on ore exports to China. Divestiture increases spot ore supply but leaves lithium output nearly unchanged, while continued trade preserves Chinese access to ore. The export ban reduces global lithium supply because refining capacity elsewhere cannot fully replace lost Chinese production. Ownership transfers do not reserve ore for domestic production; restricting Chinese access imposes a substantial supply cost at existing capacities.
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