Physical characteristics of fluorine-doped lithium oxide as advanced material for solid-electrolyte-interphase applications of lithium–air batteries

Rechargeable lithium–air batteries (LABs) are future substitutes for traditional lithium-ion batteries. However, during charge/discharge cycles, due to the unstable interface between lithium anodes and electrolytes, the Coulombic efficiency of LABs decreases, leading to their short cycle life. These restrictions can be eliminated by using the solid-electrolyte-interphase (SEI) as an anode protective layer. In this study, the major physical attributes and mechanical features of fluorine-doped lithium oxide (Li (2− x ) O (1− x ) F x ), as advanced SEI, were scrutinized through the molecular dynamics (MD) simulation method. The ionic properties of Li 2 1 - δ O 1 - δ were also probed. The results revealed that in Li 2 1 - δ O 1 - δ , the lithium vacancies were trapped by the oxygen vacancies and localized around them. This trapping process increased the activation energy barrier and declined lithium diffusivity, thereby boosting the battery charging time. Conversely, in Li (2− x ) O (1− x ) F x , there was no lithium vacancy trap due to the presence of fluoride ions. The investigation of the mechanical features of Li (2− x ) O (1− x ) F x at 300 K indicated that variations in the concentration of fluoride ions had no significant influence on the mechanical moduli (i.e., Young’s modulus). Hence, using Li (2− x ) O (1− x ) F x as an SEI layer reduces the battery charging time and self-discharge rates, increases the charge retention time, and offers acceptable mechanical properties. Graphical abstract