2-Fluoropyridine: A novel electrolyte additive for lithium metal batteries with high areal capacity as well as high cycling stability

Development of high energy density lithium metal batteries (LMBs) with high cycling stability is becoming more and more important. In this study, a novel and reliable electrolyte additive, 2-Fluoropyridine (2-FP), was successfully applied to enhance the stability of different commercial liquid electrolytes and effectively improve the performance of LMBs for the first time. The 2-FP additive was found to play a critical role in the decrease of Li nucleation as well as deposition overpotential, and finally supressing the Li-dendrites. As a result, the high-voltage LiNi1/3Mn1/3Co1/3O2 cathode (1.5 mAh cm−2)|Li metal cell using the commercial carbonate-based LiPF6 electrolyte with 2% of 2-FP additive exhibited a stable capacity retention of 67.6% even after 300-cycle test with a coulombic efficiency as high as 99.89% at 0.75 mA cm−2. Meanwhile, in the case using another commercial ether-based LiTFSI electrolyte with it, the LiFePO4 cathode (1.5 mAh cm−2)|Li metal cell also maintained long-term stability with high coulombic efficiency and the discharge capacity even with a small electrolyte amount and a high current density of 1.5 mA cm−2. By combining the surface analysis with quantum chemistry calculations, it is verified that the stabilization effect by introduction of this additive at the extreme condition was resulted from the formation of a robust and stable solid electrolyte interphase (SEI), in which the LiF and Li3N components could play a synergistic role in the improvement of SEI layer performance. Such a fluoropyridine molecule with good compatibility in the LMBs is expected to be a promising electrolyte additive for the next generation of LMBs.