Lithium Hydride is a fairly dense and easy to handle way to store hydrogen, which is one of the reasons that it’s used, with Deuterium substituting for Hydrogen, as the fusion fuel supply for thermonuclear warheads.
Well, Claudio Bruno, of the University of Rome, has begun testing the material for use in scramjet engines.
Gaseous, or for that matter cryogenic, hydrogen is bulky and difficult to store, but it also is the material that is best suited to burn quickly enough to work well under supersonic combustion.
One of the techniques used is to use a catalyst, and the heat generated at speed, to crack hydrocarbon fuels, and use the hydrogen generated, or to use a preburner, basically a ramjet inside the scramjet, to preburn the fuel and create a hot reducing atmosphere for further combustion.
LiH would decompose naturally at operating temperatures, and would appear to be a simpler solution.