Compatibility of lithium salts with solvent of the non-aqueous electrolyte in Li-O₂ batteries

The stability of lithium salts, especially in the presence of reduced oxygen species, O₂ and H₂O (even in a small amount), plays an important role in the cyclability and capacity of Li-O₂ cells. This combined experimental and computational study provides evidence that the stability of the electrolyte used in Li-O₂ cells strongly depends on the compatibility of lithium salts with solvent. In the case of the LiPF ₆-1NM3 electrolyte, the decomposition of LiPF₆ occurs in the cell as evidenced by in situ XRD, FT-IR and XPS analysis, which triggers the decomposition of 1NM3 solvent due to formation of HF from the decomposition of LiPF₆. These reactions lead to degradation of the electrolyte and cause poor cyclability of the cell. The same reactions are not observed when LiTFSI and LiCF₃SO₃ are used as the lithium salts in 1NM3 solvent, or LiPF₆ is used in TEGDME solvent.