The reversible dehydrogenation properties of the 2LiBH(4)-MgH(2) composite can be effectively improved by incorporating heterogeneous nucleation agents, typically transition metal borides. A careful study of the 2LiBH(4)-MgH(2) composite with a titanium trifluoride (TiF(3)) additive finds that using the conventional one-step milling method renders only a partial conversion from TiF(3) to titanium boride (TiB(2)) through an intermediate of titanium hydride (TiH(2)). Based on a fundamental understanding of the reaction processes of the system, we developed a three-step preparation method, which involves pre-milling the LiBH(4)-TiF(3) mixture, isothermal treatment and milling together with MgH(2). A combination of phase/chemical state/microstructural analyses using X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy techniques shows that the newly developed method can effectively promote the formation of TiB(2) and meanwhile, ensure a homogeneous dispersion of TiB(2) nanoparticles in the composite matrix. As a consequence, the composite sample prepared by the new method exhibits a favorable combination of high hydrogen capacity, fast reaction kinetics and satisfactory cyclic stability.