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Li-ion batteries have contributed to the commercial success of portable electronics and may soon dominate the electric transportation market provided that major scientific advances including new materials and concepts are developed. Classical positive electrodes for Li-ion technology operate mainly through an insertion-deinsertion redox process involving cationic species. However, this mechanism is insufficient to account for the high capacities exhibited by the new generation of Li-rich (Li(1+x)Ni(y)Co(z)Mn(1-x-y-z)O₂) layered oxides that present unusual Li reactivity. In an attempt to overcome both the inherent composition and the structural complexity of this class of oxides, we have designed structurally related Li₂Ru(1-y)Sn(y)O₃ materials that have a single redox cation and exhibit sustainable reversible capacities as high as 230 mA h g(-1). Moreover, they present good cycling behaviour with no signs of voltage decay and a small irreversible capacity. We also unambiguously show, on the basis of an arsenal of characterization techniques, that the reactivity of these high-capacity materials towards Li entails cumulative cationic (M(n+)→M((n+1)+)) and anionic (O(2-)→O₂(2-)) reversible redox processes, owing to the d-sp hybridization associated with a reductive coupling mechanism. Because Li₂MO₃ is a large family of compounds, this study opens the door to the exploration of a vast number of high-capacity materials.

Manganese-rich olivine LiFe0.33Mn0.67PO4 was proven to be an interesting electrode material for Li-ion batteries. In this paper we focus on its electrode/electrolyte reactivity that could play a role in aging processes of LiFe0.33Mn0.67PO4 //graphite cells. Positive and negative electrodes of LiFe0.33Mn0.67PO4 // graphite cells were analyzed by X-Ray Photoelectron Spectroscopy (XPS) at different steps of the first electrochemical cycle to investigate the influence of the working potential increase of this material (as compared to LiFePO4) on the formation of passivation films at the surface of both electrodes. The higher working potential of LiFe0.33Mn0.67PO4 causes an increased reactivity toward the electrolyte with a redox process between Mn3+ and carbonates solvents at the outermost surface of the electrode material. It results in a thicker interface layer with respect to LiFePO4. However this interface remains very thin. Some influence on the passivation film formed at the graphite surface was also evidenced. [ABSTRACT FROM AUTHOR]

LiFePO4 has monopolized a lot of research efforts over the past decade because it stands as an attractive positive electrode material for the next generation of Li-ion batteries to EVs/HEVs. However, issues concerning aging mechanisms need to be solved before large scale industrial production. In order to get more insight in such mechanisms, the evolution of both electrodes of a LiFePO4 // graphite cell after 200 cycles at RT and 60°C was followed using X-Ray Photoelectron Spectroscopy (XPS). The results have revealed a lack of reversibility of the Fe3+/Fe2+ redox reaction increasing upon cycling and at high temperature. In depth analyses of interfacial layers on both electrodes allowed us to further elucidate the origin of the detrimental loss of active lithium with the formation of small amounts of lithiated species either deposited or partly dissolved in the electrolyte. [ABSTRACT FROM AUTHOR]

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. It was shown to contribute to surface film formation on both electrodes of LiCoO[sub2]/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[sub2]/C, LiFePO[sub4]/C, and LiCoO[sub2]/Li[sub4]Ti[sub5]O[sub12] systems, in which the potential and the chemical nature of each electrode are changed. Coin-cells were charged at different potentials using a LiPF[sub6]/ethylene carbonate: diethyl carbonate: dimethyl carbonate liquid electrolyte with or without VC, and the electrodes were analyzed by X-ray photoelectron spectroscopy. We showed there is no interaction between the negative and positive electrodes in the VC polymerization mechanisms, for example, by exchange of chemical species from one electrode to the other, during the first charge. Separate mechanisms occur, although the same VC polymer is deposited at the surface Of both electrodes. [ABSTRACT FROM AUTHOR]

Layered Li4NiTeO6 was shown to reversibly release/uptake ∼2 lithium ions per formula unit with fair capacity retention upon long cycling. The Li electrochemical reactivity mechanism differs from that of Li2MO3 and is rooted in the Ni4+/Ni2+ redox couple, that takes place at a higher potential than conventional LiNi1−xMnxO2 compounds. We explain this in terms of inductive effect due to Te6+ ions (or the TeO66− moiety). [ABSTRACT FROM AUTHOR]

Abstract: Commercial C-LiFe0.33Mn0.67PO4 positive electrode material has been investigated by 57Fe Mössbauer Spectroscopy (MS), X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS). The combined use of these experimental techniques provides a better understanding of the electrochemical reaction involved during cycling. 57Fe MS is very efficient to directly follow oxidation state of Fe in the electrode, and gives surprisingly indirect information on the oxidation state of Mn as observed by XAS and XPS. The electrochemical mechanism is proposed based from in situ and operando investigations using both MS and XAS, and is consistent with XPS surface studies. XPS analysis of the electrodes at the end of charge (4.4V) reveals enhanced electrode/electrolyte interface reactivity at this high potential. Aging of C-LiFe0.33Mn0.67PO4/Li cells after 50cycles at 60°C indicates a rather good electrochemical behavior (low capacity fading) of the electrode material. Both 57Fe MS and XPS (Mn 2p and Fe 2p) clearly show no modification on Fe and Mn oxidation state compared to fresh electrode confirming the good electrochemical performances. [Copyright &y& Elsevier]

Abstract: The response of thin-film copper (II) ion-selective electrodes based on chalcogenide glassy Cu–Sb–Ge–Se is described according to the soaking time in a 10−4 M copper (II) solution. The chalcogenide membrane/solution interface has been investigated by using electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) in order to understand the sensing properties. During the first month of the soaking, an alteration of the membrane by a chemical change without alteration of the sensor detection performance has been observed. [Copyright &y& Elsevier]

Abstract: We have investigated the possible effect of carboxymethylcellulose (CMC) in the SEI film formation at the surface of a graphite composite electrode of LiCoO2/graphite cells. The electrode/electrolyte interface was analyzed by XPS at different potentials of the first electrochemical cycle, and after simple contact of the electrode with the electrolyte. We could evidence a specific reactivity of CMC towards the electrolyte (LiPF6 in a mixture of carbonate solvents), resulting in the formation of new species that contribute to the surface film composition. This result shows that the chemical reactivity of CMC towards the electrolyte takes part in the formation of the surface film, and contributes to the good properties of CMC as binder. [Copyright &y& Elsevier]

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]

The response of copper (II) ion-selective electrodes based on chalcogenide glassy–crystalline Cu–As–S alloys is described. The potentiometric measurements showed a Nernstian behavior in a large range of copper (II) concentration with short response time and a detection limit close to 1×10−6 M. The selectivity and the effect of the pH on the response have been determined. The chalcogenide membrane/solution interface has been investigated using electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) in order to understand the sensing properties. [Copyright &y& Elsevier]