LiFSI and LiDFBOP Dual-Salt Electrolyte Reinforces the Solid Electrolyte Interphase on a Lithium Metal Anode

Metallic lithium (Li) has great potential as an anode material for high-energy-density batteries due to its high specific capacity. However, the uncontrollable dendritic lithium growth on the metallic lithium surface limits its practical application owing to the instability of the solid electrolyte interphase (SEI). A tailored SEI composition/structure can mitigate or inhibit the lithium dendrites' growth, thereby enhancing the cyclability of the Li-metal anode. In this work, excellent cycling stability of lithium metal anodes was achieved by utilizing a novel dual-salt electrolyte based on lithium bis(fluorosulfonyl) imide (LiFSI) and lithium difluorobis(oxalato) phosphate (LiDFBOP) in carbonate solvents. By combining surface/microstructural characterization and computations, we reveal that the preferential reduction of LiDFBOP occurs prior to LiFSI and carbonate solvents and its reduction products (Li₂C₂O₄ and P-O species) bind to LiF, resulting in a favorable compact and protective SEI on the Li electrodes. It was found that the improved oxidative stability was accompanied by reduced corrosion of the current collector. A Li/Li symmetrical cell with a designed dual-salt electrolyte system exhibits stable polarization voltage over 1000 h of cycle time. In addition, the LiFSI-LiDFBOP advantage of this dual-salt electrolyte system enables the Li/LiFePO₄ cells with significantly enhanced cycling stability. This work demonstrates that constructing a tailored SEI using a dual-salt electrolyte system is vital for improving the interfacial stability of lithium metal batteries.