The Mg(BH4)(2)-xLiH (0.1 <= x <= 0.8) composites which exhibit favorable dehydrogenation and encouraging reversibility are experimentally investigated. LiH additive reduces the onset temperature for dehydrogenation to 150 degrees C. And hydrogen release exceeds 10 wt.% from the new binary material below 250 degrees C. Furthermore, rehydrogenation results show that 3.6 wt.% hydrogen can still be recharged after twenty cycles at 180 degrees C. It should be emphasized that the long-term reversibility of borohydride under 200 degrees C is long overdue. TPD, PCT, and high-pressure DSC measurements are used to characterize the improvements in thermodynamic and kinetic ways. In addition, FT-IR and NMR studies indicate that the composite has a significant synergistic effect during (de)hydrogenation processes. This work suggests that controlled cation stoichiometry combined with doping by metal Li+ subvalent to Mg2+ facilitate the formation of polyborane intermediates [B3H8](-) and [B2H6](2-). They improve the dehydrogenation properties and make the material reversible under mild conditions. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.