Formation of multi-SEI layer through Li difluoro(bisoxalato)phosphate, and Li hexafluorophosphate enhancing the performance of LMBs

Abstract

Film Li and Ni-rich electrodes with high reversible capacity are now the most expecting nominees for the materials of high energy density battery. However, owing to the vertical Li growth of Film Li during cycle, safety issues from electrolyte depletion and damage of the electrode-electrolytes interphase layer are serious. Also undesirable positive electrode-electrolyte reactions owing to low oxidation stability of the ether solvent and Structural instability of Ni-rich positive electrode hinders the application of these electrodes to the real battery. Here, we suggest that dual ion additives, having a fluorinated group can be used as an interface modifier to higher the electrochemical performance of the film Li negative electrode, while improving the oxidation stability to widen the useable voltage window of electrolytes for LMBs with working voltages above than 4 voltage area (vs. Li/Li + ). Introduction of 2 type salts lithium bis(fluorosulfonyl)imide (LiFSI) and lithium nitrate (LiNO3) in an ether-based electrolyte upgrades stability and morphology of Film Li negative electrodes. The complementary electrolyte design using both Li difluoro(bisoxalato)phosphate (LiDFBP) and Li hexafluorophosphate (LiPF6) additives induces a LiF-rich multi-interphase layer, according to the decomposition order of LUMO energy level, that can suppress the vertical growth of Film Li . And LiDFBP forms a uniform interface between positive electrode and electrolytes that limits the unwanted reaction owing to depletion of electrolytes and elutioned transition metal ions like nickel, cobalt, manganese, and aluminum. Using dual additives in dual salts ether based electrolytes greatly ameliorates capacity retention in 98.8% after 100 cycles in Li|NCM cells, which have a coulombic efficiency of 99.9%.