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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 TeO 6 6- moiety). © 2013 The Royal Society of Chemistry.

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) O 2) 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 Li 2 Ru 1-y Sn y O 3 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 (O2-→O2 2-) reversible redox processes, owing to the d-sp hybridization associated with a reductive coupling mechanism. Because Li2 MO3 is a large family of compounds, this study opens the door to the exploration of a vast number of high-capacity materials. © 2013 Macmillan Publishers Limited. All rights reserved.

Understanding the origin of the high capacity displayed by Li 2MnO3-LiMO2 (M = Ni, Co) composites is essential for improving their cycling and rate capability performances. To address this issue, the Li2Ru1-yMnyO 3 series between the iso-structural layered end-members Li 2MnO3 and Li2RuO3 was investigated. A complete solid solution was found, with the 0.4 ≤ y ≤ 0.6 members showing sustainable reversible capacities exceeding 220 mAh·g -1 centered around 3.6 V vs Li+/Li. The voltage-composition profiles display a plateau on the first charge as compared to an S-type curve on subsequent discharge which is maintained on the following charges/discharges, with therefore a lowering of the average voltage. We show this profile to evolve upon long cycling due to a structural phase transition as deduced from XRD measurements. Finally we demonstrate, via XPS measurements, the oxidation and reduction of ruthenium (Ru5+/Ru4+) during cycling together with a partial activity of the Mn4+/Mn 3+ redox couple. Moreover, we provide direct evidence for the reversibility of the O2- → O- anionic process upon cycling, hence accounting for the high capacity displayed by these materials. This work, by capturing the main redox processes pertaining to these materials, should facilitate their development. © 2013 American Chemical Society.

Li-S rechargeable batteries are attractive for electric transportation because of their low cost, environmentally friendliness, and superior energy density. However, the Li-S system has yet to conquer the marketplace, owing to its drawbacks, namely, soluble polysulfide formation. To tackle this issue, we present here a strategy based on the use of a mesoporous chromium trimesate metal-organic framework (MOF) named MIL-100(Cr) as host material for sulfur impregnation. Electrodes containing sulfur impregnated within the pores of the MOF were found to show a marked increase in the capacity retention of Li-S cathodes. Complementary transmission electron microscopy and X-ray photoelectron spectroscopy measurements demonstrated the reversible capture and release of the polysulfides by the pores of MOF during cycling and evidenced a weak binding between the polysulphides and the oxygenated framework. Such an approach was generalized to other mesoporous oxide structures, such as mesoporous silica, for instance SBA-15, having the same positive effect as the MOF on the capacity retention of Li-S cells. Besides pore sizes, the surface activity of the mesoporous additives, as observed for the MOF, appears to also have a pronounced effect on enhancing the cycle performance. Increased knowledge about the interface between polysulfide species and oxide surfaces could lead to novel approaches in the design and fabrication of long cycle life S electrodes. © 2011 American Chemical Society.