Elon Musk wants more lithium, but only a handful of countries can supply the material key to the electrification of transportation, at least for now.

The Tesla Inc. chief made a public appeal for more investment in lithium mining to close what he sees as a yawning gap between supply and demand, fueled by the adoption of electric vehicles. Musk signaled the electric car giant might finally start mining lithium due to skyrocketing prices. He first mentioned that plan almost two years ago.

The urgency to have a lineup of supply of the silvery white commodity comes as demand growth is set to surge in the coming years. While major producers such as Albemarle Corp. are expanding capacity and new projects are being built, supply growth is not fast enough due to a lack of investment…