Characterization of the passivating layer on Li[Ni0.31Co0.32Mn0.28Al0.09]O2 cathode in the overcharge state

The passivating layer (also called the solid electrolyte interface, SEI) plays a key role in the performances of Li-ion batteries. In this work, we studied the surface reactions of Li[Ni0.31Co0.32Mn0.28Al0.09]O2 with the organic electrolyte in the overcharge state by means of FTIR, XPS, XAS, and 2D correlation analysis. The FTIR and XPS results revealed that several types of compounds are formed on the cathode surface. These results also suggest that the organic solvents are decomposed to a greater extent than the Li-salt during the overcharge state. Based on the 2D correlation analysis, we can deduce the following sequence of events: 287.0 (due to C−O) → 290.0 (due to carbonate) → 288.5 (due to CO) → 291.5 (due to C−Fx) → 284.5 eV (due to CC or CH).