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LiAl x Mn 1Ϫx O 2 and LiCr x Mn 1Ϫx O 2 compounds (x Յ 0.10) with an ␣-NaFeO 2 layer-type crystal structure have been prepared by a high temperature solid-state route. The compounds are well ordered with Al or Cr sharing the Mn sites and no detectable cation mixing between Mn and Li layers. Both Al-and Cr-substituted materials cycled between 4.4 and 2.0 V in Li cells at 55ЊC show high stability of capacity. However the Al-substituted materials undergo a structural transformation to a spinel-type phase, accompanied by evolution of the discharge voltage curve to a two-plateau profile. Materials modified with small amounts of Cr show a different evolution of the discharge voltage. X-ray diffraction data for cycled LiCr x Mn 1Ϫx O 2 cathodes show that these compounds do not undergo significant transformation to spinel on cycling, but retain a hexagonal structure established on first charge.

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Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. SynopsisThis work analyses the high-strain extensional behavior of long-chain branched polyethylenes, employing two novel extensional rheometer devices, the filament stretching rheometer and the crossslot extensional rheometer. The filament stretching rheometer uses an active feedback loop to control the imposed strain rate on a filament, allowing Hencky strains of around 7 to be reached. The cross-slot extensional rheometer uses optical birefringence patterns to determine the steady-state extensional viscosity from planar stagnation point flow. The two methods probe different strain-rate regimes and in this paper we demonstrate the agreement when the operating regimes overlap and explore the steadystate extensional viscosity in the full strain-rate regime that these two complimentary techniques offer. For long-chain branched materials, the cross-slot birefringence images show a double cusp pattern around the outflow centre line (named W-cusps). Using constitutive modeling of the observed transient overshoot in extension seen in the filament stretching rheometer and using finite element simulations we show that the overshoot explains the W-cusps seen in the cross-slot extensional rheometer, further confirming the agreement between the two experimental techniques. V C 2013 The Society of Rheology.[http://dx

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Lithium manganese oxides, and in particular the spinel-structured LiMn 2 O 4 , have been investigated as potential active cathode materials for lithium ion batteries. Recently both orthorhombic and monoclinic LiMnO 2 have attracted considerable attention. It has been reported that Al doping allows the preparation of monoclinic LiAl x Mn 1−x O 2 under suitable reaction conditions, and furthermore improves the capacity retention of both o-LiAl x Mn 1−x O 2 and m-LiAl x Mn 1−x O 2 . The aim of this study was to elucidate the structural effects of Al doping with particular attention to the surface properties of the material. X-ray diffraction data reveal that Al induces monoclinic stacking faults in orthorhombic LiAl x Mn 1−x O 2 and at Al contents of ~5% the preferred cation ordering becomes that of monoclinic LiAl x Mn 1−x O 2 . X-ray photoelectron spectroscopy measurements show that the Al is homogeneously incorporated throughout the grains up to its solubility limit, and no surface enrichment of Al is observed. The XPS data indicate that Mn in the near-surface region of the material is predominantly present in its Y3 oxidation state, even when annealed to temperatures of up to 250 °C.

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