Synergistic Effects of Bisalt Additives in High-Voltage Rechargeable Lithium Batteries

The stability of high-energy-density lithium metal batteries (LMBs) heavily relies on the composition of the solid electrolyte interphase (SEI) formed on lithium metal anodes. In this study, the inorganic-rich SEI layer was achieved by incorporating bisalts additives into carbonate-based electrolytes. Within this SEI layer, the presence of LiF, polythionate, and Li₃N was observed, generated by combining 1.0 м lithium bis(trifluoromethanesulfonyl)imide in ethylene carbonate: ethyl methyl carbonate:dimethyl carbonate in a 1 : 1 : 1 volume ratio, with the addition of 2 wt% lithium difluorophosphate and 2 wt% lithium difluoro(oxalato)borate additives (EL-DO). Furthermore, this formulation effectively mitigated corrosion of aluminum current collectors. EL-DO exhibited outstanding performance, including an average coulombic efficiency of 98.2 % in Li||Cu cells and a stable discharge capacity of approximately 162 mAh g⁻¹ after 200 cycles in a Li||LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) configuration. Moreover, EL-DO displayed the potential to enhance the performance not only of LMBs but also of lithium-ion batteries. In the case of Gr||NCM811 cell using EL-DO, it consistently maintained high discharge capacities, even achieving around 135 mAh g⁻¹ after the 100^th cycle, surpassing the performance of other electrolytes. This study underscores the synergistic impact of bisalts additives in elevating the performance of lithium batteries.