Temperature effects on Li4Ti5O12 electrode/electrolyte interfaces at the first cycle: A X-ray Photoelectron Spectroscopy and Scanning Auger Microscopy study

Li4Ti5O12-based negative electrodes for Lithium-ion batteries are of interest because of the high reversibility of Li+ insertion/extraction. In this study, the surface of cycled electrodes is analysed by X-ray Photoelectron Spectroscopy (XPS) and Scanning Auger Microscopy (SAM) to investigate the effects of cycling temperature (room temperature, 60 degrees C and 85 degrees C) upon the solid electrolyte interphase (SEI) formation, which plays a major role in batteries electrochemical performances. Half-cells, with a vinylene carbonate containing electrolyte, are galvanostatically cycled at different steps of the first cycle: the mid plateau during the first discharge, the end of the first discharge at 1.2 V and the end of the first charge at 2.0 V. XPS analysis evidences that higher temperatures promote the formation of a thicker SEI, which can explain the increase of the irreversible capacity with temperature. SAM mappings (allowing high spatial resolution similar to 10-100 nm) evidence that this SEI homogeneously covers the electrode surface, regardless of the cycling temperature. During charge, the SEI is partially dissolved at room temperature, more slightly at 60 degrees C whereas at 85 degrees C, no clear evidence of layer thinning is observed. The SEI chemical composition is also investigated and reveals a majority of organic species and an increasing proportion of LiF with the temperature. (C) 2016 Elsevier B.V. All rights reserved.