Depth profile studies on nickel rich cathode material surfaces after cycling with an electrolyte containing vinylene carbonate at elevated temperature.

Lithium-ion batteries with vinylene carbonate (VC) in the electrolyte exhibit superior electrochemical and thermal behavior at elevated temperature, especially with a high Ni content in the cathode material. When VC is added to the electrolyte, polymeric species are formed on the cathode surface by a ring-opening reaction of ethylene carbonate (EC) in the electrolyte and VC, respectively. Through X-ray photoelectron spectroscopy (XPS) depth profiling, we have confirmed that these polymer layers are porous and complementary to each other. XPS results of C1s and O1s show that the outer surface and the inner layer consist of different components. Based on the XPS depth profiling results, we have suggested a reaction mechanism for the formation of a thermally stable layer on the cathode when vinylene carbonate is added to the electrolyte.