Origin of voltage decay in high-capacity layered oxide electrodes.

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.

Li(4)NiTeO(6) as a positive electrode for Li-ion batteries.

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 Ni(4+)/Ni(2+) redox couple, that takes place at a higher potential than conventional LiNi1-xMnxO2 compounds. We explain this in terms of inductive effect due to Te(6+) ions (or the TeO6(6-) moiety).

Reversible anionic redox chemistry in high-capacity layered-oxide electrodes.

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.

Increased intestinal permeability and Parkinson disease patients: chicken or egg?

UNLABELLED: Gastrointestinal involvement is a frequent and early event in the course of Parkinson Disease (PD), and may have a prominent role in the early pathophysiology of the disease. On the other hand, derangement in intestinal permeability could also result from the involvement of the gastrointestinal tract over the course of the disease. PATIENTS AND METHODS: The intestinal permeability of 12 non-selected PD patients was studied using a validated, non-invasive test; these results were compared to predefined age-adjusted reference values. RESULTS: 4/12 PD patients had abnormal gastrointestinal permeability; two had both an abnormal lactulose/mannitol ratio and an abnormal sucrose concentration, and two an isolated abnormal result. An increased lactulose/mannitol ratio is consistent with defect of either the enterocytes or the tight junctions between them. CONCLUSION: Intestinal permeability is increased in a significant proportion of unselected PD patients with minimal gastrointestinal symptoms. The significance of this finding needs to be further evaluated.

Gastrointestinal symptoms in Parkinson disease: clinical aspects and management.

Although it is now generally recognized that the clinical spectrum of Parkinson disease (PD) is broader than its defining motor aspects, its various non-motor symptoms are often not routinely assessed in the clinical setting. As most of these symptoms are amenable to treatment, improved recognition would lead to more comprehensive management of the disease, and ultimately improve the quality of life for PD patients. In an attempt to increase the general awareness of physicians caring for these patients, this article focuses on the clinical manifestations and treatment of the gastrointestinal symptoms most commonly experienced by PD patients, as well as on the gastrointestinal side effects of antiparkinsonian treatments.