Enhanced Stability at the Electrode-Electrolyte Interface in Ionic Liquid Electrolyte for 5 V Lithium-Ion Rechargeable Batteries

Lithium nickel manganese oxide (LiNi0.5Mn1.5O4) is a promising cathode material for next-generation lithium-ion rechargeable batteries due to its high operating voltage of 4.7 V vs. Li/Li+. However, there are lots of drawbacks in using LNMO as a cathode material because of the liquid electrolyte instability. When carbonate-based electrolytes are decomposed at high cut-off voltage, they generate a hydrofluoric acid which attacks the surface of LNMO. This unwanted parasitic reaction at the electrode-electrolyte interface accelerates the decay in cycle life. In this work, Ionic liquid (1M LiFSI in Pyr13FSI) is adopted as an electrolyte for LNMO cathode material. Highly stable ionic liquid mitigates dissolution of Ni and Mn even in the high cut-off voltage of 5.1 V vs. Li/Li+. X-ray fluorescence mapping analysis confirmed the mitigation of dissolution by building up a 2D image of the varying composition of a sample.