The need for higher energy density rechargeable batteries has generated interest in alkali metal electrodes paired with solid electrolytes. However, metal penetration and electrolyte fracture at low current densities have emerged as fundamental barriers. Here, we show that for pure metals in the Li-Na-K system, the critical current densities scale inversely to mechanical deformation resistance. Furthermore, we demonstrate two electrode architectures in which the presence of a liquid phase enables high current densities while preserving the shape retention and packaging advantages of solid electrodes. First, biphasic Na-K alloys show K + critical current densities (with K-β″-Al2O3 electrolyte) that exceed 15 mA⋅cm -2 . Second, introducing a wetting interfacial film of Na-K liquid between Li metal and Li6.75La3Zr1.75Ta0.25O12 (LLZTO) solid electrolyte doubles the critical current density and permits cycling at areal capacities exceeding 3.5 mAh⋅cm -2 . These design approaches hold promise for overcoming electro-chemo-mechanical stability issues that have heretofore limited performance of solid-state metal batteries.

α-Mg 3 Sb 2 is an excellent thermoelectric material through excess-Mg addition and n-type impurity doping to overcome its persistent p-type behavior. It is generally believed that the role of excess-Mg is to compensate the single Mg vacancy to realize n-type carrier conduction. In contrary to this belief, the present work indicates that the role of excess-Mg is to compensate the electronic charge of defect complex (V Mg(2) + Mg I ) 1− . The Mg solubility in α-Mg 3+x Sb 2 is quite small when only considering a single defect, but it enlarged up to x = 0.011 with the defect complex (V Mg(2) + Mg I ) 1− , which is more reasonable as supported by experiments. Under Mg-poor conditions, V Mg(1) 2− and V Mg(2) 2− are the dominant defects, and their concentrations can reach (1.05−1.18) × 10 19 cm −3 at 1200 K. Under Mg-rich conditions, (V Mg(2) + Mg I ) 1− is found to be the dominant reason for strong p-type behavior, and their concentrations can reach as high as 3.5 × 10 20 cm −3 , which shifts the Fermi level closer to the valence band maximum. The predicted carrier concentrations in the range 10 17 −10 20 cm −3 are in the same range found experimentally for pure p-type α-Mg 3 Sb 2 .

Current advances in first-principles methodology, comprehensive properties, quantitative bonding and non-polar nature were revealed for α-sulfur and validated by sulfides.

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The native point defects in the earth-abundant solar material CuSnS are studied using the hybrid functional. To generate more accurate formation energies of defects, the extended Freysoldt, Neugebauer, and Van de Walle (FNV) method is used for finite-size corrections in the charged supercell calculations. According to the calculated defect energetics, it is found that the usual experimental conditions can lead to abundant deep centers that deteriorate solar cell performance. To reduce the carrier recombination caused by the deep centers, Sn-rich and S-poor conditions should be attempted. The present calculations also give satisfactory explanations for a recent experimental work on the defect levels in CuSnS.

Density functional theory (DFT) calculations are routinely used to screen for functional materials for a variety of applications. This screening is often carried out with a few descriptors, which uses ground-state properties that typically ignores finite temperature effects. Finite-temperature effects can be included by calculating the vibrations properties and this can greatly improve the fidelity of computational screening. An important challenge for DFT-based screening is the sensitivity of the predictions to the choice of the exchange correlation function. In this work, we rigorously explore the sensitivity of finite temperature thermodynamic properties to the choice of the exchange correlation functional using the built-in error estimation capabilities within the Bayesian Error Estimation Functional (BEEF-vdw). The vibrational properties are estimated using the Debye model and we quantify the uncertainty associated with finite-temperature properties for a diverse collection of materials. We find good agreement with experiment and small spread in predictions over different exchange correlation functionals for Mg, Al 2 O 3 , Al, Ca, and GaAs. In the case of Li, Li 2 O, and 1 arXiv:1910.07891v1 [cond-mat.mtrl-sci] 4 Oct 2019NiO, however, we find a large spread in predictions as well as disagreement between experiment and functionals due to complex bonding environments. While the energetics generated by BEEF-vdW ensemble is typically normal, the complex mapping through the Debye model leads to the derived finite temperature properties having non-Gaussian behavior. We test a wide variety of probability distributions that best represent the finite temperature distribution and find that properties such as specific heat, Gibbs free energy, entropy, and the thermal expansion coefficient are well described by normal or transformed normal distributions, while the prediction spread of volume at a given temperature does not appear to be drawn from a single distribution. Given the computational efficiency of the approach, we believe that uncertainty quantification should be routinely incorporated into finite-temperature predictions. In order to facilitate this, we have open-sourced the code base, under the name, Depye.

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Recently, superhydrides have been computationally identified and subsequently synthesized with a variety of metals at very high pressures. In this work, we evaluate the possibility of synthesizing superhydrides by uniquely combining electrochemistry and applied pressure. We perform computational searches using density functional theory and particle swarm optimization calculations over a broad range of pressures and electrode potentials. Using a thermodynamic analysis, we construct pressure–potential phase diagrams and provide an alternate synthesis concept, pressure–potential (P2), to access phases having high hydrogen content. Palladium–hydrogen is a widely studied material system with the highest hydride phase being Pd3H4. Most strikingly for this system, at potentials above hydrogen evolution and ∼ 300 MPa pressure, we find the possibility to make palladium superhydrides (e.g., PdH10). We predict the generalizability of this approach for La-H, Y-H, and Mg-H with 10- to 100-fold reduction in required pressure for stabilizing phases. In addition, the P2 strategy allows stabilizing additional phases that cannot be done purely by either pressure or potential and is a general approach that is likely to work for synthesizing other hydrides at modest pressures.