Lithium and valium are both drugs used to treat mental-health disorders. Therefore, the Divalium crystals in SQ6 are a direct spoof of the Dilithium crystals used on Star Trek. In Roger's quarters, when you look at the universal translator, the narrator says "Too bad they don't make those little Dilithium watch batteries anymore.", indicating that Dilithium may have been used earlier, but later replaced by Divalium (probably either because it was better or they just ran out of / couldn't afford Dilithium).