Organic–Inorganic Hybrid SEI Induced by a New Lithium Salt for High-Performance Metallic Lithium Anodes

The practical application of the metallic lithium anode is suppressed by the highly unstable interface between electrolytes and lithium metal during the process of lithium plating/stripping. A perfect solid electrolyte interphase (SEI) can inhibit detrimental parasitic reactions, thereby improving the cycling performance of the metallic lithium anode. In this work, a high-purity solid lithium difluorobis(oxalato) phosphate (LiDFOP) is synthesized and an outstanding organic-inorganic hybrid SEI is obtained in an ether-based electrolyte for the first time induced by LiDFOP. The preferential reduction of LiDFOP can form an SEI rich in LiF and Li_xPO_yF_z species, thereby improving the conductivity and stability of the SEI. In addition, cationic-induced ring-opening polymerization between LiDFOP and 1,3-dioxolane endows the SEI with excellent adaptability to the reiterative volume change of the metallic lithium anode. Therefore, the Li/Cu battery maintains a high coulombic efficiency of 98.37% at a current density of 2 mA/cm² for 200 cycles, and the Li/Li symmetrical battery shows stable voltage hysteresis over 1000 h even under the condition of 5 mA/cm². The Li/S battery fabricated employing the electrolyte with LiDFOP shows significant improvement of cycling performance as well. These results manifest that the formation of an organic-inorganic hybrid SEI from LiDFOP can be employed as a new strategy to overcome the problem from the unstable SEI in metallic lithium batteries.