lithium is the light alkali metal from which fusion neutrons breed tritium in a blanket, making it — alongside deuterium — one of the two raw fuels of fusion energy.
The name derives from the Greek lithos, "stone": the element was identified in 1817 by Johan August Arfwedson in the mineral petalite, and it is the lightest metal in the periodic table. Natural lithium consists of two stable isotopes, and the distinction between them is what matters for fusion. Lithium-6, about 7.5 percent of natural supply, splits into helium and 📝tritium when it captures a slow neutron, releasing energy as it does; lithium-7, the abundant isotope, also yields tritium but only when struck by a fast neutron, in a reaction that consumes energy. Breeding-oriented 📝blanket designs therefore often enrich lithium-6 above its natural fraction.
Fusion's claim on lithium differs sharply from the battery market's: a power plant burns through grams of fuel per day, so its yearly lithium consumption is small against the quantities the battery industry processes. Together with 📝deuterium extracted from seawater, lithium completes the fuel story of 📝fusion — the tritium a plant actually burns is manufactured on site from this metal, which is why glossaries list lithium itself, not tritium, among fusion's primary resources.