Surface chemistry of metal oxide coated lithium manganese nickel oxide thin film cathodes studied by XPS

The effect of coating the high voltage spinel cathode LiMn1.5Ni0.5O4 with three metal oxide thin layers is discussed. Instead of the typical powder electrodes with poorly defined surface coatings, thin film electrodes were prepared with well-defined oxide coating thicknesses to investigate the influence of coating on surface reactivity via X-ray photoelectron spectroscopy (XPS). ZnO is found to decompose during the first charge whereas Al2O3 and ZrO2 are stable for more than 100 cycles. ZrO2, however, importantly limits the available Li storage capacity of the electrochemical reaction due to poorer kinetics. Al2O3 offers the best results in term of capacity retention. Upon cycling, the evidence of a signal at 75.4 eV in the Al2p binding energy spectrum indicates the partial fluorination of Al2O3 into, perhaps, Al2O2F2. Moreover, the continuous formation of ethers, esters and LixPOyFz compounds on the surface of the electrodes is found for all coating materials.

Figure optionsDownload as PowerPoint slideHighlights
► LiMn1.5Ni0.5O4 spinel thin films were prepared by RF magnetron sputtering.
► The effect of thin metal oxide coatings on cycling and surface chemistry has been studied upon cycling by X-ray photoelectron spectroscopy.
► ZrO2 limits the available storage capacity. ZnO dissolves at potentials larger than 4.7 V vs. Li/Li+. Al2O3 is stable upon long cycling.
► Ethers, esters, LiF and LixPOyFz are the main constituents of the CEI surface layer.