Effect of glutaric anhydride additive on the LiNi0.4Mn1.6O4 electrode/electrolyte interface evolution: A MAS NMR and TEM/EELS study

Abstract

Investigation of electrode/electrolyte interface of 5V spinel material LiNi0.4Mn1.6O4 was carried out in the presence of glutaric anhydride additive, using combined magic angle spinning NMR spectroscopy and electron energy-loss spectroscopy. After exposure to LiPF6 in EC/DMC liquid electrolyte, oxidation state of +III or lower has been evidenced by EELS for Mn ions, indicating that the presence of glutaric anhydride additive in the electrolyte, not only modifies the interphase, but does not prevent chemical reactions with the active material. Further investigation of the influence of the additive upon storage and cycling was performed using combined 7Li and 19F MAS NMR. The native interphase formed by simple contact of the active material with the electrolyte is partially destroyed at high potential but the new appearing interphase is overall increasing upon cycling, independently from the presence of glutaric anhydride. The use of glutaric anhydride is nevertheless beneficial as it clearly restrains the formation of lithiated interphasial species and alters the interphase composition since the formation of fluorophosphates is promoted, lowering the relative amount of resistive LiF. Although resistive LiF can be formed in significant amount, it is removed by the DMC rinsing while fluorophosphates display a stronger adherence to the active material.