Paralithium

From Memory Alpha, the free Star Trek reference

Paralithium is a substance used as a fuel for some ion-based propulsion systems, and can be converted into trilithium. The use of paralithium can be detected in a vessel's plasma emissions.

In 2373, Akritirians Vel and Piri used the paralithium on their freighter to build a trilithium explosive, which was used to bomb the Laktivia recreational facility. (VOY: "The Chute")