EwaldSolidSolution: A High-Throughput Application to Quickly Sample Stable Site Arrangements for Ionic Solid Solutions.

Data-driven materials design of ionic solid solutions often requires sampling (meta)stable site arrangements among the massive number of possibilities, which has been hampered by the lack of relevant methods. Herein, we develop a quick high-throughput sampling application for site arrangements of ionic solid solutions. Given the Ewald Coulombic energies for an initial site arrangement, EwaldSolidSolution updates the modified parts of the energy with varying sites only, which can be exhaustively estimated by using massively parallel processing. Given two representative examples of solid electrolytes, Li10GeP2S12 and Na3Zr2Si2PO12, EwaldSolidSolution successfully calculates the Ewald Coulombic energies of 211,266,225 (235,702,467) site arrangements for Li10GeP2S12 (Na3Zr2Si2PO12) with 216 (160) ion sites per unit cell in 1223.2 (1187.9) seconds: 0.0057898 (0.0050397) milliseconds per site arrangement. The computational cost is enormously saved in comparison with an existing application, which estimates the energy of a site arrangement on the second timescale. The positive correlations between the Ewald Coulombic energies and those estimated by density functional theory calculations show that (meta)stable samples are easily revealed by our computationally inexpensive algorithm. We also reveal that the different-valence nearest-neighbor pairs are distinctively formed in the low-energy site arrangements. EwaldSolidSolution will boost the materials design of ionic solid solutions by attracting broad interest.

First-Principles Study of Microscopic Electrochemistry at the LiCoO2 Cathode/LiNbO3 Coating/ß-Li3PS4 Solid Electrolyte Interfaces in an All-Solid-State Battery.

High interfacial resistance between electrode and solid electrolyte (SE) is one of the major challenges for the commercial application of all-solid-state batteries (ASSBs), and coating at the interface is an effective way for decreasing the resistance. However, microscopic electrochemistry especially for the electrochemical potential and the distribution of Li+ at the interface has not been well established yet, impeding the in-depth understanding of interfacial Li+ transport. Herein, we have introduced a potential energy profile for Li+, ηLi+, and demonstrated that the interfacial ηLi+ can be evaluated from the calculated interfacial Li vacancy formation energy or the bulk vacancy formation energy and the interface band alignment. Through computational analysis of the representative LiCoO2 cathode/LiNbO3 coating/ß-Li3PS4 SE interfaces using the novel interface structure prediction scheme based on the CALYPSO method, we found that ηLi+ at the LiCoO2/ß-Li3PS4 interface is highly disordered under the influence of the interface reconstruction and is rather electronic conductive. Insertion of LiNbO3 coating can effectively decrease the preference of ion mixing. Besides, the appropriate changes in band alignments lead to a decrease of difference in the interfacial ηLi+ and lower resistances at the interfaces. The results provide a reliable explanation for the effectiveness of the coating layer observed experimentally. Furthermore, our study provides a guidance for the future simulation of the microscopic electrochemistry at the electrode/SE interfaces in ASSBs.

Electron and Ion Transfer across Interfaces of the NASICON-Type LATP Solid Electrolyte with Electrodes in All-Solid-State Batteries: A Density Functional Theory Study via an Explicit Interface Model.

NASICON-type oxide Li1+xAlxTi2-x(PO4)3 (LATP) is expected to be a promising solid electrolyte (SE) for all-solid-state batteries (ASSBs) owing to its high ion conductivity and chemical stability. However, its interface properties with electrodes on the atomic scale remain unclear, but it is crucial for rational control of the ASSBs performance. Herein, we focused on the LATP SE with x = 0.17 and investigated the electron and ion transfer behaviors at the interfaces with the Li metal negative electrode and the LiCoO2 (LCO) positive electrode via explicit interface models and density functional theory calculations. Ti reduction was found at the LATP/Li interface. For the LATP/LCO interface, the results indicated the Li-ion transfer from LCO to LATP upon contact until a certain electric double layer is formed under equilibrium, in which LCO is partially reduced. Co-Ti exchange was also found to be favorable where the Li ion moves with Co3+ to LATP. We also explored the possible interfacial processes during annealing by simulating the oxygen removal effect and found that oxygen vacancy can be more easily formed in the LCO at the interface. It implies that partial Li ions move back to LCO for the local charge neutrality. We also demonstrated higher Li chemical potential around the LATP/LCO interfaces, leading to the dynamical Li-ion depletion upon charging. The calculation results and the deduced mechanisms well explain the experimental results so far and provide insights into the interfacial electron and ion transfer upon contact, during annealing, and charging.

Surface-Dependent Stability of the Interface between Garnet Li7La3Zr2O12 and the Li Metal in the All-Solid-State Battery from First-Principles Calculations.

The garnet-type Li7La3Zr2O12 (LLZO) solid electrolyte is of particular interest because of its good chemical stability under atmospheric condition, suitable for practical all-solid-state batteries (ASSBs). However, recent works observed electrochemical instability at the LLZO/Li interfaces. Herein, we have revealed the origin of the instability by performing a comprehensive first-principles investigation with a high-throughput interface structure search scheme, based on the density functional theory framework. Based on the constructed phase diagrams of low-index surfaces, we found that the coordinatively unsaturated (i.e. coordination number < 6) Zr sites exist widely on the low-energy LLZO surfaces. These undercoordinated Zr sites are reduced once the LLZO surface is in contact with the Li metal, leading to chemical instability of the LLZO/Li interface. Besides, the calculated formation and adhesion energies of interfaces suggest that the Li wettability on the LLZO surface is dependent on the termination structure. The employment of the approaches such as by controlling the synthesis atmosphere are needed for preventing the reduction of LLZO against the Li metal. The present analysis with comprehensive first-principles calculations provides a novel perspective for the rational optimization of the interface between LLZO electrolyte and Li metal anode in the ASSB.

A general representation scheme for crystalline solids based on Voronoi-tessellation real feature values and atomic property data.

Increasing attention has been paid to materials informatics approaches that promise efficient and fast discovery and optimization of functional inorganic materials. Technical breakthrough is urgently requested to advance this field and efforts have been made in the development of materials descriptors to encode or represent characteristics of crystalline solids, such as chemical composition, crystal structure, electronic structure, etc. We propose a general representation scheme for crystalline solids that lifts restrictions on atom ordering, cell periodicity, and system cell size based on structural descriptors of directly binned Voronoi-tessellation real feature values and atomic/chemical descriptors based on the electronegativity of elements in the crystal. Comparison was made vs. radial distribution function (RDF) feature vector, in terms of predictive accuracy on density functional theory (DFT) material properties: cohesive energy (CE), density (d), electronic band gap (BG), and decomposition energy (Ed). It was confirmed that the proposed feature vector from Voronoi real value binning generally outperforms the RDF-based one for the prediction of aforementioned properties. Together with electronegativity-based features, Voronoi-tessellation features from a given crystal structure that are derived from second-nearest neighbor information contribute significantly towards prediction.

Bayesian-Driven First-Principles Calculations for Accelerating Exploration of Fast Ion Conductors for Rechargeable Battery Application.

Safe and robust batteries are urgently requested today for power sources of electric vehicles. Thus, a growing interest has been noted for fabricating those with solid electrolytes. Materials search by density functional theory (DFT) methods offers great promise for finding new solid electrolytes but the evaluation is known to be computationally expensive, particularly on ion migration property. In this work, we proposed a Bayesian-optimization-driven DFT-based approach to efficiently screen for compounds with low ion migration energies ([Formula: see text]. We demonstrated this on 318 tavorite-type Li- and Na-containing compounds. We found that the scheme only requires ~30% of the total DFT-[Formula: see text] evaluations on the average to recover the optimal compound ~90% of the time. Its recovery performance for desired compounds in the tavorite search space is ~2× more than random search (i.e., for [Formula: see text] < 0.3 eV). Our approach offers a promising way for addressing computational bottlenecks in large-scale material screening for fast ionic conductors.

Informatics-Aided Density Functional Theory Study on the Li Ion Transport of Tavorite-Type LiMTO4F (M(3+)-T(5+), M(2+)-T(6+)).

The ongoing search for fast Li-ion conducting solid electrolytes has driven the deployment surge on density functional theory (DFT) computation and materials informatics for exploring novel chemistries before actual experimental testing. Existing structure prototypes can now be readily evaluated beforehand not only to map out trends on target properties or for candidate composition selection but also for gaining insights on structure-property relationships. Recently, the tavorite structure has been determined to be capable of a fast Li ion insertion rate for battery cathode applications. Taking this inspiration, we surveyed the LiMTO4F tavorite system (M(3+)-T(5+) and M(2+)-T(6+) pairs; M is nontransition metals) for solid electrolyte use, identifying promising compositions with enormously low Li migration energy (ME) and understanding how structure parameters affect or modulate ME. We employed a combination of DFT computation, variable interaction analysis, graph theory, and a neural network for building a crystal structure-based ME prediction model. Candidate compositions that were predicted include LiGaPO4F (0.25 eV), LiGdPO4F (0.30 eV), LiDyPO4F (0.30 eV), LiMgSO4F (0.21 eV), and LiMgSeO4F (0.11 eV). With chemical substitutions at M and T sites, competing effects among Li pathway bottleneck size, polyanion covalency, and local lattice distortion were determined to be crucial for controlling ME. A way to predict ME for multiple structure types within the neural network framework was also explored.

Global minimum structure search in Li(x)CoO2 composition using a hybrid evolutionary algorithm.

The global minimum structures for Li(x)CoO(2) compositions where 0 ≤ x ≤ 1 were probed by using a hybrid evolutionary algorithm with an underlying ab initio structural relaxation scheme. The method successfully predicted experimentally observed variants of layered configurations at various degrees of lithiation and the spinel (Fd3[combining macron]m) phase at x = 1/2. New low-energy non-layered host structures at x < 1/2 were also revealed. These structures can be formed from the usual layered configuration through coherent stacking faults along the c-axis and the migration of Co ions into the Li-poor intercalation layer.

Synthesis and characterization of polyhedral Pt nanoparticles: their catalytic property, surface attachment, self-aggregation and assembly.

In this paper, we presented the preparation procedure of Pt nanoparticles with the well-controlled polyhedral morphology and size by a modified polyol method using AgNO(3) in accordance with the reduction of H(2)PtCl(6) in EG at high temperature around 160°C. The methods of UV-vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and high resolution (HR) TEM measurements were used to characterize their surface morphology, size, and crystal structure. We have observed that the polyhedral Pt nanoparticles of sharp edges and corners were produced in the preferential homogenous growth as well as the formation of porous and large Pt particles by self-aggregation and assembly originating from as-prepared polyhedral Pt nanoparticles. It is most impressive to find that the arrangement of Pt nanoparticles was observed in their surface attachments, self-aggregation, random and directed surface self-assembly by the bottom-up approach. Their high electrocatalytic activity for methanol oxidation was predicted. The findings and results showed that the polyhedral Pt nanoparticle-based catalysts exhibited the high electrocatalytic activity for their potential applications in developing the efficient Pt-based catalysts for direct methanol fuel cells.

Synthesis of Porous Single-Crystalline Platinum Nanocubes Composed of Nanoparticles.

Single-crystalline platinum nanocubes with porous morphology were synthesized for the first time by using ethylene glycol, HCl, and polyvinylpyrrolidone as the reducing agents of H2PtCl6. The morphology and size distribution of the Pt particles formed were studied with a high-resolution transmission electron microscope and selected-area electron diffraction pattern. By controlling the material concentrations and reaction temperature and period, Pt single crystals about 5 nm in size were formed in the first stage of the reduction process that had {100} facets, which were stacked one on top of the other, forming porous nanocubes 20-80 nm in length. The synthesized Pt nanocubes exhibited enhanced catalytic activity for methanol oxidation.