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Abstract: Sputtered vanadium pentoxide thin films have been used as positive electrode in lithium microbatteries and extensively studied after cycling over the 31st galvanostatic cycles by two complementary techniques, especially well-adapted for thin films analysis: X-ray photoelectron spectroscopy and atomic force microscopy. This study is mainly focussed on the characterization of the surface film (solid electrolyte interface-type) which is formed during subsequent discharges and charges and especially on its composition and its morphology that are changing during cycling. First, the growth of a surface layer between the positive electrode and the liquid electrolyte has been evidenced upon the discharge as well as its partial dissolution upon the charge. Secondly, the chemical and topographic changes of this interfacial layer at various stages of cycling are discussed in correlation with the evolution of the discharge capacity over cycles. [Copyright &y& Elsevier]

Abstract: Research into new negative electrode materials as an alternative to carbonaceous materials brings new questions about electrode/electrolyte interface mechanisms. For graphite, these mechanisms have great importance on the ageing phenomena. What about intermetallic alloys, such as Cu–Sn systems? The nature of the electrode and its potential of lithium ions uptake (different from graphite) may have a great influence on the passivation film formed at the surface of the electrode. In this paper, we report on the XPS study of the electrode/electrolyte interface of a Cu6Sn5-based electrode. The main difference with graphite is not the nature and composition of the passivation layer, but its poor dependence on the electrochemical reaction during cycling. [Copyright &y& Elsevier]

Abstract: In this paper, we report on a study of the electrode/electrolyte interfaces of a LiCoO2/C cell using XPS (X-ray photoelectron spectroscopy). The originality of our work lies in detailed investigations step by step during the first cycle. The results have shown that the formation process of the SEI takes place in different successive stages that are dependent on the potential of the cell. It clearly appears that SEI formation continues in the potential range where lithium ion intercalation proceeds in the carbon electrode. Salt degradation products are formed after solvent decomposition ones. Concerning the LiCoO2/electrolyte interface, the results obtained have shown the formation of a very thin film on the active material but not on the binders. In all cases, the novel XPS approach applied in the lab, combining core peaks and valence band analyses, allows a precise characterization of the main chemical species of the interface layers. On the basis of these results and in conjunction with literature data, the degradation mechanisms have been discussed. [Copyright &y& Elsevier]