Novel Concentrated Li[(FSO₂)(n-C₄F₉SO₂)N]-Based Ether Electrolyte for Superior Stability of Metallic Lithium Anode

Lithium (fluorosulfonyl)(n-nonafluorobutanesulfonyl)imide [Li[(FSO 2 )(n-C 4 F 9 SO 2 )N] (LiFNFSI)] is investigated as a conducting salt, which can form a relatively stable solid-electrolyte-interphase film in concentrated ether electrolyte to achieve favorable protection for lithium metal anodes. Li|Cu and Li|Li cells with concentrated LiFNFSI-based electrolyte have been demonstrated to display high average Coulombic efficiency (≈97%) and excellent cycling stability (over 1,000 h) of metallic lithium anodes, compared to concentrated lithium bis(trifluoromethanesulfonyl)imide [Li[N(SO 2 CF 3 ) 2 ] (LiTFSI)]-based electrolyte. The morphologies and compositions of the lithium–metal anode surface are also comparatively analyzed by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. Moreover, superior electrochemical performance in the concentrated LiFNFSI-based electrolyte for Li|LiFePO 4 cells is also presented herein. These results indicate that concentrated LiFNFSI-based electrolyte is a promising candidate for metallic lithium rechargeable batteries.