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Huang, Wenxuan

Publications and source records attributed to Huang, Wenxuan.

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Hidden structural and chemical order controls lithium transport in cation-disordered oxides for rechargeable batteries

Structure plays a vital role in determining materials properties. In lithium ion cathode materials, the crystal structure defines the dimensionality and connectivity of interstitial sites, thus determining lithium ion diffusion kinetics. In most conventional cathode materials that are well-ordered, the average structure as seen in diffraction dictates the lithium ion diffusion pathways. Here, we show that this is not the case in a class of recently discovered high-capacity lithium-excess rocksalts. An average structure picture is no longer satisfactory to understand the performance of such disordered materials. Cation short-range order, hidden in diffraction, is not only ubiquitous in these long-range disordered materials, but fully controls the local and macroscopic environments for lithium ion transport. Our discovery identifies a crucial property that has previously been overlooked and provides guidelines for designing and engineering cation-disordered cathode materials.

36 MATERIALS SCIENCE↗
DOE OSTI2017

First-Principles Study of the Voltage Profile and Mobility of Mg Intercalation in a Chromium Oxide Spinel

The development of Mg batteries, which can potentially achieve higher energy densities than Li-ion systems, is in need of cathodes that can reversibly intercalate Mg 2+ and exhibit a higher energy density than the state-of-the-art Chevrel and thio-spinel cathodes. Recent theoretical and experimental studies indicate that the oxide spinel family presents a set of promising Mg cathodes. Here specifically, in this work, we investigate Mg intercalation into the spinel-MgxCr 2 O 4 system. Using first-principles calculations in combination with a cluster expansion model and the nudged elastic band theory, we calculate the voltage curve for Mg insertion at room temperature and the activation barriers for Mg diffusion, respectively, at different Mg concentrations in the Cr 2 O 4 structure. Our results identify a potential limitation to Mg intercalation in the form of stable Mg-vacancy orderings in the Cr 2 O 4 lattice, which exhibit high migration barriers for Mg diffusion in addition to a steep voltage change. Additionally, we propose cation substitution as a potential mechanism that can be used to suppress the formation of the stable Mg-vacancy ordering, which can eventually enable the practical usage of Cr 2 O 4 as a Mg-cathode.

25 ENERGY STORAGE↗
DOE OSTI2017

First-Principles Simulation of the (Li–Ni–Vacancy)O Phase Diagram and Its Relevance for the Surface Phases in Ni-Rich Li-Ion Cathode Materials

Despite several reports on the surface phase transformations from a layered to a disordered spinel and a rock-salt structure at the surface of the Ni-rich cathodes, the precise structures and compositions of these surface phases are unknown. The phenomenon, in itself, is complex and involves the participation of several contributing factors. Of these factors, transition metal (TM) ion migration toward the interior of the particle and hence formation of TM-densified surface layers, triggered by oxygen loss, is thermodynamically probable. Here in this study, we simulate the thermodynamic phase equilibria as a function of TM ion content in the cathode material in the context of lithium nickel oxides, using a combined approach of first-principles density functional calculations, the cluster expansion method, and grand canonical Monte Carlo simulations. We developed a unified lattice Hamiltonian that accommodates not only rock-salt like structures but also topologically different spinel-like structures. Also, our model provides a foundation to investigate metastable cation compositions and kinetics of the phase transformations. Our investigations predict the existence of several Ni-rich phases that were, to date, unknown in the scientific literature. Our simulated phase diagrams at finite temperature show a very low solubility range of the prototype spinel phase. Finally, we find a partially disordered spinel-like phase with far greater solubility that is expected to show very different Li diffusivity compared to that of the prototype spinel structure.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Construction of ground-state preserving sparse lattice models for predictive materials simulations

First-principles based cluster expansion models are the dominant approach in ab initio thermodynamics of crystalline mixtures enabling the prediction of phase diagrams and novel ground states. However, despite recent advances, the construction of accurate models still requires a careful and time-consuming manual parameter tuning process for ground-state preservation, since this property is not guaranteed by default. In this paper, we present a systematic and mathematically sound method to obtain cluster expansion models that are guaranteed to preserve the ground states of their reference data. The method builds on the recently introduced compressive sensing paradigm for cluster expansion and employs quadratic programming to impose constraints on the model parameters. The robustness of our methodology is illustrated for two lithium transition metal oxides with relevance for Li-ion battery cathodes, i.e., Li 2x Fe 2(1-x) O 2 and Li 2x Ti 2(1-x) O 2 , for which the construction of cluster expansion models with compressive sensing alone has proven to be challenging. We demonstrate that our method not only guarantees ground-state preservation on the set of reference structures used for the model construction, but also show that out-of-sample ground-state preservation up to relatively large supercell size is achievable through a rapidly converging iterative refinement. This method provides a general tool for building robust, compressed and constrained physical models with predictive power.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Fast Mg 2+ diffusion in Mo 3 (PO 4 ) 3 O for Mg batteries

In this work, we identify a new potential Mg battery cathode structure Mo 3 (PO 4 ) 3 O, which is predicted to exhibit ultra-fast Mg 2+ diffusion and relatively high voltage based on first-principles density functional theory calculations. Nudged elastic band calculations reveal that the migration barrier of the percolation channel is only ~80 meV, which is remarkably low, and comparable to the best Li-ion conductors. This low barrier is verified by ab initio molecular dynamics and kinetic Monte Carlo simulations. The voltage and specific energy are predicted to be ~1.98 V and ~173 W h kg -1 , respectively. If confirmed by experiments, this material would have the highest known Mg mobility among inorganic compounds.

25 ENERGY STORAGE↗