The electronic structures and energies of neutral and anionic (LiBH4)(x) clusters (x= 1-5) have been systematically studied by using density functional theory with the B3LYP/6-311++ G(d, p) level. For investigating the importance of excess electrons on hydrogen storage capacity, the interactions between hydrogen atoms and the anionic (LiBH4)(x) clusters are also examined. The calculated formation energies of the anionic clusters show that the anionic clusters have a high thermal stability. It is found that hydrogen atoms are adsorbed on the anionic (LiBH4)(x) clusters chemically with adsorption energies in the range of 69.13 - 153.73 kcal/mol. The hydrogen storage capacity can be improved from 18.51% to 19.26 -22.12% in weight percent depending on the size of various anionic (LiBH4)(x) clusters. Our calculation results show that the existence of excess electrons on the (LiBH4)(x) clusters can enhance the hydrogen storage capacity. The Mulliken charge analysis was performed to illustrate the interactions between H atoms and the anionic (LiBH4)(x) clusters. Copyright (C) 2016 John Wiley & Sons, Ltd.