DFT Study on the Li Mobility in Li-Ion-Based Solid-State Electrolytes

Abstract

We have investigated the diffusion mechanisms of Li-ion in amorphous lithium phosphite (LiPO₃) with the addition of sulphur. By applying the nudge elastic band (NEB)¹ method in crystal LiPO₃ and Li₃PO₄, we have confirmed the ease in diffusion pathways for Li ions in LiPO₃ which is quite consistent with the previous theoretical finding. From our diffusion study in 0.5 Li₂O- 0.5 P₂O₅ and 0.4 Li₂SO₄ – 0.6 (Li₂O-P₂O₅) melts above 3000K investigated with ab-initio molecular dynamics (AIMD) has been confirmed by experiments at lower temperatures, we have demonstrated the benefit of S addition in increasing the Li⁺ mobility. We have also found that the Li₂SO₄ addition into the glass result in a characteristic shift in Li-ion vibration to a lower vibrational frequency. In addition, the presence of oxygen surrounding the diffusion pathways appears to be essential in assisting the Li⁺ mobility in both crystalline and amorphous structures.