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Abstract: Oxide ion conduction and phase transition phenomena have been investigated on La2−xPbxMo2O9−x/2 solid solutions (x≤0.6). X-ray and neutron diffraction experiments as well as thermal analyses indicate that a single phase of high-temperature polymorph (β-phase) is preserved down to room temperature for the composition of x≥0.06. In the solid solution range, ionic conductivity gradually decreases with Pb-substitution. Such phase transition and ionic conduction properties of La2−xPbxMo2O9−x/2 are quite similar to the Bi-substituted system, La2−xBixMo2O9, although ionic conductivity at lower temperatures is slightly higher in the former system than the latter with the same-amount of substitution. Room temperature neutron diffraction experiment suggests that oxide-ion deficiency is introduced mainly into O2 site by the charge compensation with Pb-substitution, which would contribute to a little enhancement in conductivity compared with Bi-substituted samples along with the variation of nearest O2 O3 bond length. [Copyright &y& Elsevier]

The search for new materials that could improve the energy density of Li-ion batteries (LIB) is one of today's most challenging issues. Recently, cation-disordered lithium-excess metal oxides have emerged as a promising new class of cathode materials for LIB, due to their high reversible capacities and nice structural stability. However, a full structural model of the Li-transition metal (TM) sharing sublattice and the origin of short range ordering (SRO) of cations requires further investigation. In this work, we put forward a Monte Carlo strategy of building cation-disordered rocksalt material supercell models. The cations of Li 1.0 Ti 0.5 Ni 0.5 O 2 (LTNO) are placed at the FCC sublattice sites with the constraint of Pauling's electroneutrality rule, instead of a random way. This constraint causes the Li-Ti and Ni-Ni clustering. Based on this model, we discussed the relationship between the SRO, the local distorting, the theoretical capacity and the order-disorder strengths. A unified understanding of these factors in cation-disordered materials may enable a better design of disordered-electrode materials with high capacity and high energy density. • In this work, we described a Monte Carlo strategy to build the model of cation-disordered material Li 1.0 Ti 0.5 Ni 0.5 O 2. The cations are distributed at the FCC sublattice with a constraint of Pauling's electroneutrality rule, instead of a random way. The model is relaxed by an atomistic force field to get into the thermal equilibrium. • We conclude that the electroneutrality causes the short-range ordering (SRO) in the cation sublattice and results the Li-Ti and Ni-Ni clustering. • The SRO is favoured by the lattice completeness and lower the local distortion of the cations. But it also decreases the content of 0-TM channels and the capacities of the materials. So we can expect for a more 'disordered' material with larger capacity. The energy calculation shows that this can be done by sintering the materials at higher temperatures which has been proved by several experiments. [ABSTRACT FROM AUTHOR]

Here, we propose a new two-dimensional (2D) monolayer YS 2 and investigate its properties as electrode material for Li-ion and Na-ion batteries (LIBs and NIBs), by combining the density functional theory (DFT) and the crystal structure prediction techniques. The results of phonon dispersion and ab-initio molecular dynamics (AIMD) simulations confirm that it is dynamically and thermally stable. The adsorption energies of Li and Na on YS 2 are −2.038 and −1.939 eV, respectively. Besides, the superior electrical conductivity is maintained during the whole lithiation/sodiumation process. The calculated diffusion energy barriers for Li and Na on this YS 2 monolayer are 0.33 and 0.24 eV, respectively, demonstrating a fast ion transfer rate. The theoretical specific capacities for Li and Na adatoms on YS 2 are both 350 mA h g−1, comparable to the graphite electrode. These features indicate that 2D YS 2 monolayer could be considered as a promising electrode material for both LIBs and NIBs. Unlabelled Image • We predicted a new 2D transition metal disulfide (TMD), namely, YS 2 monolayer. • The YS 2 keeps metallic during the whole lithiation/sodiumation process. • The diffusion barrier of Li-ion (Na-ion) for YS 2 is 0.33 (0.24) eV. • The theoretical specific capacities for Li and Na atoms on YS 2 are both 350 mA h g−1. [ABSTRACT FROM AUTHOR]