Sarium krellide
From Memory Alpha, the free Star Trek reference
Sarium krellide was a material which stored large amounts of energy and which was usually used in power cells or explosives. (TNG: "In Theory")
The maximum energy density of sarium krellide was 1.3x10E6 megajoules per cubic centimeter, leaking less than 1.05 kilojoules per hour. (Star Trek: The Next Generation Technical Manual pg 134)
Clancium oxide compounds were preferred to conventional sarium krellide explosives because of superior thermal dispersion characteristics in low-pressure atmospheres. (TNG: "Night Terrors")
