Intercalation Chemistry of the Disordered Rocksalt Li₃V₂O₅ Anode from Cluster Expansions and Machine Learning Interatomic Potentials

Disordered rocksalt (DRX) Li3V2O5 is a promising anode candidate for rechargeable lithium-ion batteries because of its low voltage, high rate capability, and good cycling stability. Herein, we present a comprehensive study of the intercalation chemistry of the DRX-Li3V2O5 anode using density functional theory (DFT) calculations combined with machine learning cluster expansions and interatomic potentials. The predicted voltage profile of the DRX Li3V2O5 anode at room temperature based on Monte Carlo simulations with a fitted cluster expansion model is in good agreement with experiments. In contrast to previous DFT results, we find that Li ions predominately intercalate into tetrahedral sites during charging, while a majority of Li and V ions at octahedral sites remain stable. In addition, molecular dynamics simulations with a fitted moment tensor potential attribute the fast-charging capability of DRX-Li3V2O5 to the facile diffusivity of Li+ via a tetrahedral–octahedral–tetrahedral pathway. We further suggest tuning the Li:V ratio as a means of trading off increased lithiation capacity and decreased anode voltage in this system. This work provides in-depth insights into the high-performance DRX-Li3V2O5 anode and paves the way for the discovery of other disordered anode materials

First Principles Study of the Li₁₀GeP₂S₁₂ Lithium Super Ionic Conductor Material

First Principles Study of the Li₁₀GeP₂S₁₂ Lithium Super Ionic Conductor Materia

SI2-SSI: Collaborative Research: A Robust High-throughput Ab initio Computation and Analysis Software Framework for Interface Materials Science

<div>A three-year SI2-SSI project is proposed to develop an open-source Ab initio Interface Materials Computation and Analysis in Python (aimcapy) software framework for data-driven interface materials science. This framework will be built on the existing pymatgen, pymatgen-db, custodian and FireWorks software libraries, integrating them into a complete, user-friendly, and flexible system for high-throughput (HT) ab initio computations and analysis. This SSI will greatly expand the capabilities of this framework beyond ground state bulk electronic structure and energy calculations, targeting developmental efforts on three key focus areas of great interest to interface materials science: (i) Ab-initio thermodynamics of surfaces and interfaces; ii) Advanced methods for materials kinetics and diffusion at materials interfaces; and iii) Automated algorithms for structural construction of grain boundary and post data-processing and analysis. Ultimately, to expand its usage to various research areas, the proposed aimcapy software framework will be designed to interface with any energy evaluation engines (ab initio and force-field-based classical mechanics codes) with minimal changes of the source.</div

Rational Composition Optimization of the Lithium-Rich Li₃OCl_1–<i>x</i>Br_<i>x</i> Anti-Perovskite Superionic Conductors

The newly discovered lithium-rich antiperovskite (LRAP) superionic conductors are an extremely interesting class of materials with potential applications as solid electrolytes in Li-ion batteries. In this work, we present a rational composition optimization strategy for maximizing the Li⁺ conductivity in the LRAP guided by a combination of first-principles calculations and percolation theory. Using nudged elastic band (NEB) calculations, we show that a Cl-rich channel with Br-rich end points configuration leads to low vacancy migration barriers in the LRAP structure. By incorporating the halide-environment-dependent NEB barriers in a bond percolation model, we predict that there are potentially higher conductivity Li₃OCl_1–<i>x</i>Br_<i>x</i> structures near 0.235 ≤ <i>x</i> ≤ 0.395. This prediction is confirmed by AIMD simulation that finds Li₃OCl_0.75Br_0.25 to have a higher Li⁺ conductivity than Li₃OCl_0.5Br_0.5, the highest conductivity LRAP identified experimentally thus far. These results highlight that there is scope for further enhancing the conductivity in the LRAP chemistry. The general approach developed can potentially be extended to other ion-conducting systems, such as the structurally similar perovskite oxygen-ion conductors of interest in solid-oxide fuel cells as well as other superionic conductors

SI2-SSI: Collaborative Research: A Robust High-throughput Ab initio Computation and Analysis Software Framework for Interface Materials Science

Poster for NSF SI2 workshop. Award#: NSF ACI-1550404</div

Role of Critical Oxygen Concentration in the β‑Li₃PS_4–<i>x</i>O_<i>x</i> Solid Electrolyte

Lithium superionic conductors are the critical enabling component for next-generation all-solid lithium-ion batteries. In particular, the β polymorph of Li3PS4 has attracted major interest due to its combination of excellent ionic conductivity and passivating interfacial stability with Li. In this work, we systematically investigated the effect of oxygenation in β-Li3PS4 to further enhance its ionic conductivity and electrochemical stability using density functional theory calculations and ab initio molecular dynamics simulations. We predict that a maximum ionic conductivity of 1.52 mS cm–1 (and minimum activation energy) can be achieved at x = 0.25 in Li3PS4–xOx which is about 7 times higher than that of β-Li3PS4. This increase in ionic conductivity can be attributed to the flattening of the potential energy surface due to the diversification of the Li chemical environments by the S–O mixed-anionic framework, resulting in a change from quasi-2D to 3D Li diffusion. We highlight that the spatial localization of the electrostatic potential is a qualitative descriptor to assess the migration barrier of the charge carrier in the S–O mixed framework. These microscopic analyses shed light on the role of critical oxygen concentration to tune the rate-performance of mixed-anion lithium superionic conductors

Li₃Y(PS₄)₂ and Li₅PS₄Cl₂: New Lithium Superionic Conductors Predicted from Silver Thiophosphates using Efficiently Tiered Ab Initio Molecular Dynamics Simulations

We report two novel, earth-abundant lithium superionic conductors, Li₃Y­(PS₄)₂ and Li₅PS₄Cl₂, that are predicted to satisfy the necessary combination of good phase stability, high Li⁺ conductivity, wide band gap and good electrochemical stability for solid electrolyte applications in all-solid-state rechargeable lithium-ion batteries. These candidates were identified from a high-throughput first-principles screening of the Li–P–S ternary and Li–M–P–S (where M is a non-redox-active element) quaternary chemical spaces, including candidates obtained by replacing Ag with Li in the Ag–P–S and Ag–M–P–S chemical spaces. An efficient tiered screening strategy was developed that combines topological analysis with <i>ab initio</i> molecular dynamics simulations to exclude rapidly candidates unlikely to satisfy the stringent conductivity requirements of lithium superionic conductors. In particular, we find Li₃Y­(PS₄)₂ to be an extremely promising candidate exhibiting a room-temperature Li⁺ conductivity of 2.16 mS/cm, which can be increased multifold to 7.14 and 5.25 mS/cm via aliovalent doping with Ca²⁺ and Zr⁴⁺, respectively. More critically, we show that the phase and electrochemical stability of Li₃Y­(PS₄)₂ is expected to be better than current state-of-the-art lithium superionic conductors

A Facile Mechanism for Recharging Li₂O₂ in Li–O₂ Batteries

Li–air is a novel battery technology with the potential to offer very high specific energy, but which currently suffers from a large charging overpotential and low power density. In this work, we use ab initio calculations to demonstrate that a facile mechanism for recharging Li₂O₂ exists. Rather than the direct decomposition pathway of Li₂O₂ into Li and O₂ suggested by equilibrium thermodynamics, we find an alternative reaction pathway based on topotactic delithiation of Li₂O₂ to form off-stoichiometric Li_2–<i>x</i>O₂ compounds akin to the charging mechanism in typical Li-ion intercalation electrodes. The low formation energy of bulk Li_2–<i>x</i>O₂ phases confirms that this topotactic delithiation mechanism is rendered accessible at relatively small overpotentials of ∼0.3–0.4 V and is likely to be kinetically favored over Li₂O₂ decomposition. Our findings indicate that at the Li₂O₂ particle level there are no obstacles to increase the current density, and point to an exciting opportunity to create fast charging Li–air systems

Nanoscale Stabilization of Sodium Oxides: Implications for Na–O₂ Batteries

The thermodynamic stability of materials can depend on particle size due to the competition between surface and bulk energy. In this Letter, we show that, while sodium peroxide (Na₂O₂) is the stable bulk phase of Na in an oxygen environment at standard conditions, sodium superoxide (NaO₂) is considerably more stable at the nanoscale. As a consequence, the superoxide requires a much lower nucleation energy than the peroxide, explaining why it can be observed as the discharge product in some Na–O₂ batteries. As the superoxide can be recharged (decomposed) at much lower overpotentials than the peroxide, these findings are important to create highly reversible Na–O₂ batteries. We derive the specific electrochemical conditions to nucleate and retain Na-superoxides and comment on the importance of considering the nanophase thermodynamics when optimizing an electrochemical system

Elucidating Structure–Composition–Property Relationships of the β‑SiAlON:Eu²⁺ Phosphor

In this work, we performed a systematic investigation of structure–composition–property relationships in Eu2+-activated β-SiAlON, one of the most promising narrow-band green phosphors for high-power light-emitting diodes and liquid crystal display backlighting with wide color gamut. Using first-principles calculations, we identified and confirmed various chemical rules for Si–Al, O–N, and Eu activator ordering within the β-SiAlON structure. Through the construction of energetically favorable models based on these chemical rules, we studied the effect of oxygen content and Eu2+ activator concentrations on the local EuN9 activator environment, and its impact on important photoluminescence properties such as emission peak position (using the band gap as a proxy), bandwidth, and thermal quenching resistance. Increasing oxygen content is shown to lead to an increase in Eu–N bond lengths and distortion of the EuN9 coordination polyhedron, modifying the crystal field environment of the Eu2+ activator, and resulting in red-shifting and broadening of the emission. We also show that the calculated excited band structure of β-SiAlON exhibits a large gap between the 5d levels and the conduction band of the host, indicating a large barrier toward thermal ionization (>0.5 eV) and, hence, excellent thermal quenching stability. Based on these insights, we discuss potential strategies for further composition optimization of β-SiAlON