Although Li-rich layered oxides (Li1+xNiyCozMn1-x-y-zO2 > 250 mAh g(-1)) are attractive electrode materials providing energy densities more than 15% higher than today's commercial Li-ion cells, they suffer from voltage decay on cycling. To elucidate the origin of this phenomenon, we employ chemical substitution in structurally related Li2RuO3 compounds. Li-rich layered Li2Ru1-yTiyO3 phases with capacities of ~240 mAh g(-1) exhibit the characteristic voltage decay on cycling. A combination of transmission electron microscopy and X-ray photoelectron spectroscopy studies reveals that the migration of cations between metal layers and Li layers is an intrinsic feature of the charge-discharge process that increases the trapping of metal ions in interstitial tetrahedral sites. A correlation between these trapped ions and the voltage decay is established by expanding the study to both Li2Ru1-ySnyO3 and Li2RuO3; the slowest decay occurs for the cations with the largest ionic radii. This effect is robust, and the finding provides insights into new chemistry to be explored for developing high-capacity layered electrodes that evade voltage decay.

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AESTRACTThe microstructure of the ordered perovskite Ba(MgIl3Ta2j3)O3 was studied by means of direct imaging, using high-resolution electron microscopy, and by means of selected-area electron diffraction. 'Single' crystals are shown to be fragmented at different structural levels. The cubic Ba03 framework contains numerous twins and stacking faults. Single domains of this framework are further fragmented by the potential occurrence of four orientation variants and of three translation variants in each orientation variant of the superstructure. The observations are consistent with the assumption that, at a temperature close to the melting point, an order-disorder transition of the B-cation sublattice occurs within the already-formed Ba03 framework. 2 f 2+ 5+

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In the average structure of Mo2.065S3 there are two crystallographically independent zig‐zag chains of molybdenum atoms (Mo–Mo = 2.86 Å). X‐ray and electron diffraction studies show that the zig‐zag chains are distorted in such a way that “four‐atom” clusters of Mo are formed; the displacements of the Mo atoms from the average structure are mainly along the chain axes and amount to 0.16 Å. The deformed structure can be described by two independent k vectors which are incommensurate above ≈︁ 150 K. Important changes in the diffraction patterns are noticed at ≈︁ 390, 180, and ≈︁ 110 K. A refinement of the structure at 110 K (k1 = [0, 1/2, 3/4], k2 = [1/2, 1/2, 0] shows that k1 is associated with the distortions in one of the two types of zig‐zag chains, the distortions in the other zig‐zag chain being responsible for the k2 satellites. The behaviour of the satellites can be interpreted in terms of the creation of correlation between the order in adjacent chains, i.e. due to “phase ordering”.