Structural and electronic properties of small lithium peroxide clusters in view of the charge process in Li–O2 batteries

Abstract

The Li–O₂ battery is an ideal energy storage device due to its highest theoretical energy density; however, its high charge overpotential limits its practical application. Herein, through ab initio calculations, we systematically investigated the structural and electronic properties of small (Li₂O₂)_n^m+ (n = 1, m = 0, 1 and n = 2, m = 0, 1, and 2) clusters and calculated the reaction energies of various decomposition reactions. Results show that the (Li₂O₂)₁ monomer has a low spin, whereas the (Li₂O₂)₂ dimer has a high spin. The analysis of bond length, molecular orbitals, and projected density of states reveals that the interaction of O–O is stronger in the cationic cluster than in the neutral one, whereas the interaction of O–Li is weaker in the cationic cluster than in the neutral one; this facilitates the decomposition of cationic lithium peroxide cluster. Furthermore, the calculated reaction energies indicate that the peroxide lithium decomposition preferentially favors two-step reaction over one-step reaction. Finally, the lowest-energy reaction pathway for the decomposition of (Li₂O₂)₂ dimer was predicted to be (Li₂O₂)₂ → Li₂O₂ → (Li₂O₂)⁺ → LiO₂ → O₂, and the rate-determining step was predicted to be the first step.