Category: Publications

Publications

Polarons in Vanadium Oxides

Jasleen’s first-author paper on “Polaron-induced metal-to-insulator transition in vanadium oxides from density functional theory calculations” is out in Physical Review B! Vanadium oxides are promising phase-change memory units for neuromorphic computing due to their metal-insulator transitions (MIT) at or near room temperature. In this work, we show that V3O5 exhibits very low hole and electron polaron migration barriers (< 100 meV) compared to V2O3 and VO2, leading to much higher estimated polaronic conductivity. The relative migration barriers are found to be related to the amount of distortion that has to travel when the polaron migrate from one site to another. Polarons in V3O5 also have smaller binding energies to vanadium and oxygen vacancy defects. These results explain recent experiment studies showing the injection of charge carriers into vanadium oxides as an alternative switching mechanism and also potentially as a means to tune the MIT temperature. Check out this work here.

Publications

The intercalation chemistry of DRX-Li3V2O5 anode

Xingyu’s swansong work in the Materials Virtual Lab, “Intercalation Chemistry of the Disordered Rocksalt Li3V2O5 Anode from Cluster Expansions and Machine Learning Interatomic Potentials” has been published in Chemistry of Materials! We revisited the intercalation chemistry of the highly promising DRX-Li3V2O5 using machine learning-based computational techniques that enable much larger scale simulations. DRX Li3V2O5 is a promising anode candidate for rechargeable lithium-ion batteries because of its low voltage, high rate capability, and good cycling stability. In contrast to previous DFT studies, we show that insertion of Li primarily occurs in the tetrahedral sites and that the voltage profile depends critically on the initial Li/V disorder. MD simulations also show that DRX-Li3V2O5 has a fast Li diffusivity, which depends on the concentration of Li. We propose 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. Check out the work here.

Publications

Matterverse.ai and M3GNet Universal IAP

Dr Chi Chen’s swansong work in our group, “A Universal Graph Deep Learning Potential for the Periodic Table” is now published in Nature Computational Science! Interatomic potentials (IAPs), which describe the potential energy surface of atoms, are a fundamental input for atomistic simulations. However, existing IAPs are either fitted to narrow chemistries or too inaccurate for general applications. In this work, we combine graph neural networks with traditional 3-body interactions to develop a flexible, yet accurate architecture for machine learning of materials properties. Using the massive database of structural relaxations performed by the Materials Project over the past ten years, we train a universal IAP for 89 elements of the periodic table with broad applications in structural relaxation, dynamic simulations and property prediction of materials across diverse chemical spaces. Using the new capabilities of the M3GNet universal IAP, we are proud to launch matterverse.ai, a ML database of yet-to-be-synthesized materials. Matterverse.ai currently contains about 31 million hypothetical crystal structures, of which about 1.8 million materials were identified to be potentially stable. The database also provides ML properties using state-of-the-art multi-fidelity MEGNet models, such as experimental, HSE and PBE band gaps, bulk and shear moduli, etc. Check out the article here. […]

Publications

Interfacial Stability of NMC cathodes

Congrats to Hideyuki Komatsu, our visiting scientist from Nissan, on his first author work “Interfacial Stability of Layered LiNixMnyCo1−x−yO2 Cathodes with Sulfide Solid Electrolytes in All-Solid-State Rechargeable Lithium-Ion Batteries from First-Principles Calculations” published in the Journal of Physical Chemistry C! In this work, we explore the relationship between the composition of layered LiNixMnyCo1−x−yO2 (NMC) cathodes and interfacial stability in all-solid-state lithium-ion batteries. A key insight is that the broader commercial trend towards high Ni content to reduce cost leads to significantly more reactive interfaces with the Li6PS5Cl argyrodite solid electrolyte. This suggests that current efforts to reduce the Co content in cathodes may compromise potential applications in all-solid-state architectures. Nevertheless, we find that common SEI phases such as Li2CO3, surface phases such as NiO, and oxide buffer layers such as LiNbO3 can provide effective protection between NMC and LPSCl. Check out the work here.

Publications

Interfacial Stability of Lithium Sulfur Batteries

Congratulations to Manas Likhit Holekevi Chandrappa, Ji Qi, Chi Chen and Swastika Banerjee on the publication of “Thermodynamics and Kinetics of the Cathode−Electrolyte Interface in All-Solid-State Li−S Batteries” in the Journal of the American Chemical Society! Lithium−sulfur batteries (LSBs) use cheap and abundant sulfur in place of expensive metal-based cathodes. Using a solid electrolyte in place of traditional liquid electrolytes mitigates polysulfide shuttling, a key impediment to LSB commercialization. In this work, we present a comprehensive study of the thermodynamics and kinetics of the cathode−electrolyte interface in all-solid-state LSBs. Using DFT calculations, we show that among the major solid electrolyte chemistries (oxides, sulfides, nitrides, and halides), sulfides are the most stable solid electrolytes against the S cathode, as well as the most promising buffer layers if the use of other SE chemistries is desired. Finally, MD simulations with an accurate machine learning interatomic potential revealed that the most stable Li3PS4(100)/S interfaces form 2D channels with lower activation barriers for Li diffusion. These results provide critical new insights into the cathode−electrolyte interface design for next-generation all-solid-state LSBs. We gratefully acknowledge Nissan Motor Inc and Nissan North America for their generous support for this work! This work has been published open access […]

Publications

CdS/V3O5 for Neuromorphic Computing

Congratulations to Jasleen on her first co-author paper on “An Optoelectronic Heterostructure for Neuromorphic Computing: CdS/V3O5” in Applied Physics Letters! Nonvolatile resistive switching is one of the key phenomena for emerging applications in optoelectronics and neuromorphic computing. However, the stochastic nature of the ion migration can be an impediment for the device robustness and controllability, with uncontrolled variations of high and low resistance states or threshold voltages. In this work, we report an optically induced resistive switching based on a CdS/V3O5 heterostructure. V3O5 is known to have a second order insulator to metal transition around 415 K, with an electrically induced threshold switching at room temperature. Upon illumination, the direct transfer of the photoinduced carriers from the CdS into V3O5 produces a nonvolatile resistive switching at room temperature. Jasleen’s contribution is in using DFT calculations to understand the defects present in V3O5 and the effects of electron doping. We show that electrons (generated by CdS under illumination) injected in V3O5 are trapped in a deep state, slowing the “low” temperature relaxation rate. For the LT phase (T < 340 K), the photoexcited electrons trapped into the oxygen vacancy are unable to overcome the barrier, and therefore, no relaxation is observed. […]

Publications

Universal ML model for GB energies

Weike’s swansong project in our group on “A Universal Machine Learning Model for Elemental Grain Boundary Energies” has just been published in Scripta Materialia! The grain boundary (GB) energy has a profound influence on the grain growth and properties of polycrystalline metals. Here, we show that the energy of a GB, normalized by the bulk cohesive energy, can be described purely by four geometric features to within a mean absolute error of 0.13 Jm-2 . More importantly, this universal GB energy model can be extrapolated to the energies of high Σ GBs without loss in accuracy. These results highlight the importance of capturing fundamental scaling physics and domain knowledge in the design of interpretable, extrapolatable machine learning models for ma­terials science. Check out this work here.

Publications

Cover art for Chemistry of Materials

Mahdi’s cover art for his recent paper “MxLa1-xSiO2-yNz (M = Ca/Sr/Ba): Elucidating and Tuning the Structure and Eu2+ Local Environments to Develop Full-Visible Spectrum Phosphors” has been selected for the Front Cover of Chemistry of Materials!

Publications

Efficient near-infrared phosphors

Efficient near-infrared (NIR) LEDs are used in many applications, including medical diagnostics, food detection, security monitoring, and machine vision. In this collaborative work with the group of Prof Rong-jun Xie at Xiamen University published in Matter, Mahdi Amachraa developed descriptors of the Eu(II)-host interactions to predict the 5d-to-4f energy gap with a RMSE of 7.0 nm. By incorporating this predictor into a high-throughput screening of 223 nitride materials in the Inorganic Crystal Structure Database, we identified and experimentally validated (Sr,Ba)3Li4Si2N6:Eu(II) with NIR emissions of 800- 830 nm and high quantum efficiencies (QEs) of 30%-40%. This NIR emitter has 3x more power than prevailing NIR emitters. We demonstrate that the ultralong emission wavelength and high QE stem from a coordinated energy transfer and an optimized electronic delocalization around Eu(II). Check out this work here.

Publications

DRX Li3Nb2O5 Electrode

Our collaborative work with the group of Prof Claire Xiong on “Electrochemically induced amorphous-to-rock-salt phase transformation in niobium oxide electrode for Li-ion batteries” has been published in Nature Materials! In this work, we report a nanostructured rock-salt Nb2O5 electrode formed through an amorphous-to-crystalline transformation during repeated electrochemical cycling with Li+. This electrode can reversibly cycle three lithiums per Nb2O5, corresponding to a capacity of 269 mAh/g at 20 mA/g, and retains a capacity of 191 mAh/g at a high rate of 1 A/g. The main contribution from Yunxing Zuo of the Materials Virtual Lab is using DFT computations to show that the cubic rock-salt framework promotes the percolation of low-energy migration paths. We also develop a computable metric to identify other transition metal oxides with a likelihood of rock-salt formation. Our work suggests that inducing crystallization of amorphous nanomaterials through electrochemical cycling is a promising avenue for creating unconventional high-performance metal oxide electrode materials. Check out the publication here.