We report the results of the first-principles calculation on the intermediate compounds of LiBH₄. The stability of LiB₃H₈ and Li₂BnHn (n=5–12) has been examined with the ultrasoft pseudopotential method based on the density-functional theory. Theoretical prediction has suggested that monoclinic Li₂B₁₂H₁₂ is the most stable among the candidate materials. We propose the following hydriding (dehydriding) process of LiBH₄ via this intermediate compound: LiBH₄ 1/2Li₂B₁₂H₁₂+5/6LiH+13/12H₂ LiH+B+3/2H₂. The hydrogen content and enthalpy of the first reaction are estimated to be 10 mass % and 56 kJ/mol H₂, respectively, and those of the second reaction are 4 mass % and 125 kJ/mol H₂. They are in good agreement with experimental results of the thermal desorption spectra of LiBH₄. Our calculation has predicted that the bending modes for the Γ-phonon frequencies of monoclinic Li₂B₁₂H₁₂ are lower than that of LiBH₄, while stretching modes are higher. These results are very useful for the experimental search and identification of possible intermediate compounds
