"Lithium" is all over the episode, I'm afraid.
SULU: That was one of our lithium crystal circuits, sir.
SULU: Another lithium circuit. Now supplementing with battery power, sir.
SCOTT: I don't know, sir. With those three lithium crystals gone.
SCOTT: One lithium crystal left, and that with a hairline split at the base.
SPOCK: The entire ship's power is feeding through one lithium crystal.
SPOCK: There's a lithium mining operation on Rigel 12. High-grade ore, I've heard.
KIRK: Notify them that we'll need the lithium crystals immediately upon arrival.
KIRK: Captain's log-- Stardate 1330.1. Position, fourteen hours out of Rigel 12. We're on auxiliary impulse engines. Fuel low, barely sufficient to achieve orbit over the planet. Lithium replacements are now imperative. The effect of Mudd's women on my crew continues to grow, still totally unexplained. Harry Mudd is confined to his quarters under guard.