Synthesis method of alpha-aluminum trihydride

The invention provides a synthesis method of alpha-aluminum trihydride, which comprises the following steps of: step 1, adding bis (bromomethyl) benzene into an anhydrous ether solution of lithium aluminum hydride, and reacting in an inert atmosphere to obtain an aluminum trihydride ether complex after the reaction is finished; and step 2, conveying the aluminum trihydride diethyl ether complex into toluene, carrying out deetherification precipitation, filtering, washing a filter cake, and drying the filter cake to obtain alpha-aluminum trihydride. According to the synthesis method, the used raw material bis (bromomethyl) benzene is easy to purify, the problems that the raw materials contain impurities such as FeCl3, are difficult to purify, are sensitive to moisture in air and the like are solved, a byproduct LiBr generated in the synthesis process is dissolved in a solvent diethyl ether, and an intermediate AlH3. N [(C2H5) 2O] solution in the synthesis process can be directly subjected to ether removal and