High-pressure synthesis of solid solutions between trigonal LiNiO2 and monoclinic Li[Li1/3Ni2/3]O-2.

High-pressure synthesis in an oxygen-rich atmosphere yields solid solutions between LiNiO2 and Li2NiO3 over the whole concentration range. Structural characterization of the high-pressure oxides was performed using powder XRD, SEM analysis, IR spectroscopy, EPR spectroscopy at 9.23 and 115GHz and magnetic susceptibility measurements. The crystal structure of Li[LixNi1x]O2 ,0pxp1 3; changes from trigonal R-3m to monoclinic C2/m at Li-to-Ni ratio of 2 (or x ¼ 1 3). The incorporation of Li into NiO2-layers causes a decrease in the mean Li-O and Ni1–xLix–O bond distance. Li and Ni ions in the mixed Ni1–xLixO2-layers display a tendency to order at a short length scale in such a way that mimics the Li1/3Ni2/3-arrangment of the end Li[Li1/3Ni2/3]O2 composition. The charge distribution in these oxides proceeds via Ni3+ and Ni4+ ions

High-Frequency EPR Analysis of the Local Structure and Oxidation State of Ni and Mn in Ni,Mn co-doped LiCoO2

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High-pressure synthesis and electrochemical behavior of layered (1-a)LiNi1-yAlyO2 center dot aLi[Li1/3Ni2/3]O-2 oxides.

Layered ð1 aÞLiNi1yAlyO2 aLi½Li1=3Ni2=3O2 oxides, 0pao0:4, have been prepared by solid state reaction between NiO,\ud Al2O3 and Li2O2 under high pressure. The structural characterization of the layered oxides was performed using powder XRD, IR\ud spectroscopy and EPR spectroscopy at 9.23 and 115 GHz. It has been found that the high-pressure favors Al substitution for Ni in\ud the NiO2-layers of layered LiNiO2. A random Al/Ni distribution in the layer was found. The incorporation of extra Li in the\ud Ni1yAlyO2-layer starts at a precursor composition Li=ðNi þ AlÞ41:2. While pure NiO2-layers are able to incorporate under highpressure\ud up to 1/3Li, the appearance of Al in the NiO2-layers hinders Liþ dissolution ðLioð1 yÞ=3Þ. In addition, with increasing Al\ud content there is a strong cationic mixing between the layers. High-frequency EPR of Ni3þ indicates that the structural interaction of\ud LiAlyNi1yO2 with Li½Li1=3Ni2=3O2 proceeds via the formation of domains comprising different amount of Ni3þ ions. The use of\ud Li1:08Al0:09Ni0:83O2 as a cathode material in a lithium ion cells displays a first irreversible Li extraction at 4.8 V, after which a\ud reversible lithium insertion/extraction between 3.0 and 4.5V is observed on further cycling

High-pressure synthesis and electrochemical behavior of layered (1-a)LiNi1-yAlyO2 center dot aLi[Li1/3Ni2/3]O-2 oxides.

Layered ð1 aÞLiNi1yAlyO2 aLi½Li1=3Ni2=3O2 oxides, 0pao0:4, have been prepared by solid state reaction between NiO, Al2O3 and Li2O2 under high pressure. The structural characterization of the layered oxides was performed using powder XRD, IR spectroscopy and EPR spectroscopy at 9.23 and 115 GHz. It has been found that the high-pressure favors Al substitution for Ni in the NiO2-layers of layered LiNiO2. A random Al/Ni distribution in the layer was found. The incorporation of extra Li in the Ni1yAlyO2-layer starts at a precursor composition Li=ðNi þ AlÞ41:2. While pure NiO2-layers are able to incorporate under highpressure up to 1/3Li, the appearance of Al in the NiO2-layers hinders Liþ dissolution ðLioð1 yÞ=3Þ. In addition, with increasing Al content there is a strong cationic mixing between the layers. High-frequency EPR of Ni3þ indicates that the structural interaction of LiAlyNi1yO2 with Li½Li1=3Ni2=3O2 proceeds via the formation of domains comprising different amount of Ni3þ ions. The use of Li1:08Al0:09Ni0:83O2 as a cathode material in a lithium ion cells displays a first irreversible Li extraction at 4.8 V, after which a reversible lithium insertion/extraction between 3.0 and 4.5V is observed on further cycling

DFT+U Calculations and XAS Study: Further Confirmation of the Presence of CoO 5

International audienceLiCoO2, one of the major positive electrode materials for Li-ion batteries, can be synthesized with excess Li. Previous experimental work suggested the existence of intermediate spin (IS) Co3+ ions in square-based pyramids to account for the defect in this material. We present here a theoretical study based on density functional theory (DFT) calculations together with an X-ray absorption spectroscopy (XAS) experimental study. In the theoretical study, a hypothetical Li4Co2O5 material, where all the Co ions are in pyramids, was initially considered as a model material. Using DFT+U, the intermediate spin state of the Co3+ ions is found stable for U values around 1.5 eV. The crystal and electronic structures are studied in detail, showing that the defect must actually be considered as a pair of such square-based pyramids, and that Co-Co bonding can explain the position of Co in the basal plane. Using a supercell corresponding to more diluted defects (as in the actual material), the calculations show that the IS state is also stabilized. In order to investigate experimentally the change in the electronic structure in the Li-overstoichiometric LiCoO2, we used X-ray absorption near edge structure (XANES) spectroscopy and propose an interpretation of the O Kedge spectra based on the DFT+U calculations, that fully supports the presence of pairs of intermediate spin state Co3+ defects in Li-overstoichiometric LiCoO2

Positive Electrode Materials for Li-Ion and Li-Batteries

Positive electrodes for Li-ion and lithium batteries (also termed "cathodes") have been under intense scrutiny since the advent of the Li-ion cell in 1991. This is especially true in the past decade. Early on, carbonaceous materials dominated the negative electrode and hence most of the possible improvements in the cell were anticipated at the positive terminal; on the other hand, major developments in negative electrode materials made in the last portion of the decade with the introduction of nanocomposite Sn/C/Co alloys and Si-C composites have demanded higher capacity positive electrodes to match. Much of this was driven by the consumer market for small portable electronic devices. More recently, there has been a growing interest in developing Li-sulfur and Li-air batteries that have the potential for vastly increased capacity and energy density, which is needed to power large-scale systems. These require even more complex assemblies at the positive electrode in order to achieve good properties. This review provides an overview of the major developments in the area of positive electrode materials in both Li-ion and Li batteries in the past decade, and particularly in the past few years. Highlighted are concepts in solid-state chemistry and nanostructured materials that conceptually have provided new opportunities for materials scientists for tailored design that can be extended to many different electrode materials.close61253