The effect of vinylene carbonate (VC) as electrolyte additive on the formation mechanisms of passivation films covering both electrodes in lithium-ion batteries was investigated by X-ray photoelectron spectroscopy (XPS). LiConormalO2 /graphite coin cells using a LiPnormalF6 /ethylene carbonate:diethyl carbonate:dimethyl carbonate liquid electrolyte with or without VC were charged at 20 and 60°C . The identification of VC-derived products formed at the surface of the electrodes was carried out by a dual experimental/theoretical approach. From a classical XPS core peak analysis completed by a detailed interpretation and simulation of valence spectra supported by ab initio calculations, and through direct synthesis of the VC polymer, we could evidence the formation of the radical poly(VC) at the electrode/electrolyte interfaces. We showed that the radical polymerization is the main reaction mechanism of VC contributing to the formation of the passivation layers at the surface of both electrodes.

The impact of aluminum oxide coatings on LiCoO 2 materials for commercial lithium ion batteries has been investigated by X-ray photoelectron spectroscopy ͑XPS͒. A low binding energy component in the Al 2p core peak spectra was observed and attributed to the formation of a LiAl x Co ͑1−x͒ O 2 solid solution interphase for both Al 2 O 3 -and AlPO 4 -coated LiCoO 2 . The surface chemistry of pristine and Al 2 O 3 -coated LiCoO 2 cathodes and graphite anodes have been investigated after cycling up to 4.2 V or 4.4 V cutoff voltage and after various levels of capacity fade. The Al 2 O 3 coating enhances the capacity retention at both 4.2 V and 4.4 V cutoff voltages. XPS analyses provided evidence of the inhibition of cobalt dissolution from the LiCoO 2 positive electrode by the aluminum coatings. Moreover, the Al 2 O 3 coating lowers the kinetics of degradation of electrolyte species, especially the LiPF 6 salt.

Vinylene Carbonate (VC) is a commonly used electrolyte additive in Li-ion batteries, because of its beneficial role on the formation of the solid electrolyte interphase (SEI). It was shown to contribute to surface film formation on both electrodes of LiCoO 2 /C cells via its radical polymerization mechanism. In this paper, we carried out a comparative study of the role of VC on electrode/electrolyte interfaces in LiCoO 2 /C, LiFePO 4 /C and LiCoO 2 /Li 4 Ti 5 O 12 systems, in which the potential and the chemical nature of each electrode are changed. Coincells were charged at different potentials using a LiPF 6 /EC:DEC:DMC liquid electrolyte with or without VC, and the electrodes were analyzed by X-ray Photoelectron Spectroscopy (XPS).We showed there is no interaction between the negative and the positive electrode in the VC polymerization mechanisms -for example by exchange of chemical species from one electrode to the other one -during the first charge. Separate mechanisms occur, although the same VC polymer is deposited at the surface of both electrodes.