SIMES Publications
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"Incorporating the Nanoscale Encapsulation Concept from Liquid Electrolytes into Solid-State Lithium–Sulfur Batteries" — Xin Gao: Xueli Zheng, Jingyang Wang, Zewen Zhang, Xin Xiao, Jiayu Wan, Yusheng Ye, Lien-Yang Chou, Hiang Kwee Lee, Jiangyan Wang, Rafael A. Vilá, Yufei Yang, Pu Zhang, Lin- Wang Wang, Yi Cui; Nano Letters, 06/15/20.
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Xueli Zheng, Jingyang Wang, Zewen Zhang, Xin Xiao, Jiayu Wan, Yusheng Ye, Lien-Yang Chou, Hiang Kwee Lee, Jiangyan Wang, Rafael A. Vilá, Yufei Yang, Pu Zhang, Lin- Wang Wang, Yi Cui
Abstract
Solid-state Li−S batteries are attractive due to their high energy density and safety. However, it is unclear whether the concepts from liquid electrolytes are applicable in the solid state to improve battery performance. Here, we demonstrate that the nanoscale encapsulation concept based on Li2S@TiS2 core−shell particles, originally developed in liquid electrolytes, is effective in solid polymer electrolytes. Using in situ optical cell and sulfur Kedge X-ray absorption, we find that polysulfides form and are welltrapped inside individual particles by the nanoscale TiS2 encapsulation. This TiS2 encapsulation layer also functions to catalyze the oxidation reaction of Li2S to sulfur, even in solid-state electrolytes, proven by both experiments and density functional theory calculations. A high cell-level specific energy of 427 W·h· kg−1 is achieved by integrating the Li2S@TiS2 cathode with a poly(ethylene oxide)-based electrolyte and a lithium metal anode. This study points to the fruitful direction of borrowing concepts from liquid electrolytes into solid-state batteries.
"Tortuosity Effects in Lithium-Metal Host Anodes" — HaoChen: Allen Pei, Jiayu Wan, Dingchang Lin, Rafael Vilá, Hongxia Wang, David Mackanic, Hans-Georg Steinrück, William Huang, Yuzhang Li, Ankun Yang, Jin Xie, Yecun Wu, Hansen Wang, YiCui; Joule, 04/15/20.
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Allen Pei, Jiayu Wan, Dingchang Lin, Rafael Vilá, Hongxia Wang, David Mackanic, Hans-Georg Steinrück, William Huang, Yuzhang Li, Ankun Yang, Jin Xie, Yecun Wu, Hansen Wang, YiCui
Abstract
Lithium (Li) metal is the ultimate anode material for Li batteries because of its highest capacity among all candidates. Recent research has focused on stable interphase and host materials to address its low stability and reversibility. Here, we discover that tortuosity is a critical parameter affecting the morphology and electrochemical performances of hosted Li anodes. In three types of hosts—vertically aligned, horizontally aligned, and random reduced graphene oxide (rGO) electrodes with tortuosities of 1.25, 4.46, and 1.76, respectively—we show that high electrode tortuosity causes locally higher current density on the top surface of electrodes, resulting in thick Li deposition on the surface and degraded cycling performance. Low electrode tortuosity in the vertically aligned rGO host enables homogeneous Li transport and uniform Li deposition across the host, realizing greatly improved cycling stability. Using this principle of low tortuosity, the designed electrode shows through-electrode uniform morphology with anodic Coulombic efficiency of ∼99.1% under high current and capacity cycling conditions.

"Electrochemical generation of liquid and solid sulfur on two-dimensional layered materials with distinct areal capacities" — Ankun Yang: Guangmin Zhou, Xian Kong, Rafael A. Vilá, Allen Pei, Yecun Wu, Xiaoyun Yu, Xueli Zheng, Chun-Lan Wu, Bofei Liu, Hao Chen, Yan Xu, Di Chen, Yanxi Li, Sirine Fakra, Harold Y. Hwang, Jian Qin, Steven Chu & Yi Cui; Nature Nanotechnology, 01/27/20.
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Guangmin Zhou, Xian Kong, Rafael A. Vilá, Allen Pei, Yecun Wu, Xiaoyun Yu, Xueli Zheng, Chun-Lan Wu, Bofei Liu, Hao Chen, Yan Xu, Di Chen, Yanxi Li, Sirine Fakra, Harold Y. Hwang, Jian Qin, Steven Chu & Yi Cui
Abstract
It has recently been shown that sulfur, a solid material in its elementary form S8, can stay in a supercooled state as liquid sulfur in an electrochemical cell. We establish that this newly discovered state could have implications for lithium–sulfur batteries. Here, through in situ studies of electrochemical sulfur generation, we show that liquid (supercooled) and solid elementary sulfur possess very different areal capacities over the same charging period. To control the physical state of sulfur, we studied its growth on two-dimensional layered materials. We found that on the basal plane, only liquid sulfur accumulates; by contrast, at the edge sites, liquid sulfur accumulates if the thickness of the two-dimensional material is small, whereas solid sulfur nucleates if the thickness is large (tens of nanometres). Correlating the sulfur states with their respective areal capacities, as well as controlling the growth of sulfur on two-dimensional materials, could provide insights for the design of future lithium–sulfur batteries.
"Unravelling Degradation Mechanisms and Atomic Structure of Organic-Inorganic Halide Perovskites by Cryo-EM" — Yanbin Li: Weijiang Zhou, Yuzhang Li, Wenxiao Huang, Zewen Zhang, Guangxu Chen, Hansen Wang, Gong-Her Wu, Nicholas Rolston, Rafael Vila, Wah Chiu, and Yi Cui; Joule, 11/20/19.
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Weijiang Zhou, Yuzhang Li, Wenxiao Huang, Zewen Zhang, Guangxu Chen, Hansen Wang, Gong-Her Wu, Nicholas Rolston, Rafael Vila, Wah Chiu, and Yi Cui
Abstract
Despite rapid progress of hybrid organic-inorganic halide perovskite solar cells, using transmission electron microscopy to study their atomic structures has not been possible because of their extreme sensitivity to electron beam irradiation and environmental exposure. Here, we develop cryoelectron microscopy (cryo-EM) protocols to preserve an extremely sensitive perovskite, methylammonium lead iodide (MAPbI3) under various operating conditions for atomic-resolution imaging. We discover the precipitation of lead iodide nanoparticles on MAPbI3 nanowire’s surface after short UV illumination and surface roughening after only 10 s exposure to air, while these effects remain undetected in conventional X-ray diffraction. We establish a definition for critical electron dose and find this value for MAPbI3 at cryogenic condition to be 12 e−/Å2 at 1.49 Å spatial resolution. Our results highlight the importance of cryo-EM since traditional techniques cannot capture important nanoscale changes in morphology and structure that have important implications for perovskite solar cell stability and performance.
"Cryo-EM Structures of Atomic Surfaces and Host-Guest Chemistry in Metal-Organic Frameworks" — Yuzhang Li: Kecheng Wang, Weijiang Zhou, Yanbin Li, Rafael Vila, William Huang, Hongxia Wang, Guangxu Chen, Gong-Her Wu, Yuchi Tsao, Hansen Wang, Robert Sinclair, Wah Chiu, Yi Cui; Matter, 08/07/19.
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Kecheng Wang, Weijiang Zhou, Yanbin Li, Rafael Vila, William Huang, Hongxia Wang, Guangxu Chen, Gong-Her Wu, Yuchi Tsao, Hansen Wang, Robert Sinclair, Wah Chiu, Yi Cui
Abstract
Host-guest interactions govern the chemistry of a broad range of functional materials, but direct imaging using conventional transmission electron microscopy has not been possible. This problem is exacerbated in metal-organic framework materials, which are easily damaged by the electron beam. Here, we use cryogenic electron microscopy (cryo-EM) to stabilize the host-guest structure and resolve the atomic surface of zeolitic imidazolate framework (ZIF-8) and its interaction with guest CO2 molecules. We image step-edge sites on the ZIF-8 surface that provide insight to its growth behavior. Furthermore, we observe two distinct binding sites for CO2 within the ZIF-8pore, which are predicted by density functional theory to be energetically favorable. This CO2 insertion induces an apparent ~3% lattice expansion along the <002> and <011> directions of the ZIF-8 unit cell. The ability to stabilize and preserve host-guest chemistry opens a rich materials space for scientific exploration and discovery using cryo-EM.
"Corvus: a framework for interfacing scientific software for spectroscopic and materials science applications" — S. M. Story: F. D. Vila, J. J. Kas, K. B. Raniga, C. D. Pemmaraju and J. J. Rehr; Journal of Synchrotron Radiation, 07/24/19.
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F. D. Vila, J. J. Kas, K. B. Raniga, C. D. Pemmaraju and J. J. Rehr
Abstract
Corvus, a Python-based package designed for managing workflows of physical simulations that utilize multiple scientific software packages, is presented. Corvus can be run as an executable script with an input file and automatically generated or custom workflows, or interactively, in order to build custom workflows with a set of Corvus-specific tools. Several prototypical examples are presented that link density functional, vibrational and X-ray spectroscopy software packages and are of interest to the synchrotron community. These examples highlight the simplification of complex spectroscopy calculations that were previously limited to expert users, and demonstrate the flexibility of the Corvus infrastructure to tackle more general problems in other research areas.
"Velocity-gauge real-time TDDFT within a numerical atomic orbital basis set" — K. Gilmore: F.D. Vila, J.J. Kas, S.A. Sato, J.J. Rehr, K. Yabana, David Prendergast; Computer Physics Communications, 02/07/18.
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F.D. Vila, J.J. Kas, S.A. Sato, J.J. Rehr, K. Yabana, David Prendergast
Abstract
We present an efficient implementation of the Bethe–Salpeter equation (BSE) method for obtaining core-level spectra including X-ray absorption (XAS), X-ray emission (XES), and both resonant and non-resonant inelastic X-ray scattering spectra (N/RIXS). Calculations are based on density functional theory (DFT) electronic structures generated either by abinit or Quantumespresso, both plane-wave basis, pseudopotential codes. This electronic structure is improved through the inclusion of a GW self energy. The projector augmented wave technique is used to evaluate transition matrix elements between core-level and band states. Final two-particle scattering states are obtained with the NIST core-level BSE solver (NBSE). We have previously reported this implementation, which we refer to as ocean(Obtaining Core Excitations from Ab initio electronic structure and NBSE) (Vinson et al., 2011). Here, we present additional efficiencies that enable us to evaluate spectra for systems ten times larger than previously possible; containing up to a few thousand electrons. These improvements include the implementation of optimal basis functions that reduce the cost of the initial DFT calculations, more complete parallelization of the screening calculation and of the action of the BSE Hamiltonian, and various memory reductions. Scaling is demonstrated on supercells of SrTiO3 and example spectra for the organic light emitting molecule Tris-(8-hydroxyquinoline)aluminum (Alq3) are presented. The ability to perform large-scale spectral calculations is particularly advantageous for investigating dilute or non-periodic systems such as doped materials, amorphous systems, or complex nano-structures.
"Emergence of Interfacial Polarons from Electron–Phonon Coupling in Graphene/h-BN van der Waals Heterostructures" — Chaoyu Chen: José Avila, Shuopei Wang, Yao Wang, Marcin Mucha-Kruczyński, Cheng Shen, Rong Yang, Benjamin Nosarzewski, Thomas P. Devereaux,,○ Guangyu Zhang, and Maria Carmen Asensio; Nano Letters, 01/05/18.
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José Avila, Shuopei Wang, Yao Wang, Marcin Mucha-Kruczyński, Cheng Shen, Rong Yang, Benjamin Nosarzewski, Thomas P. Devereaux,,○ Guangyu Zhang, and Maria Carmen Asensio
Abstract
van der Waals heterostructures, vertical stacks of layered materials, offer new opportunities for novel quantum phenomena which are absent in their constituent components. Here we report the emergence of polaron quasiparticles at the interface of graphene/hexagonal boron nitride (h-BN) heterostructures. Using nanospot angleresolved photoemission spectroscopy, we observe zone-corner replicas of h-BN valence band maxima, with energy spacing coincident with the highest phonon energy of the heterostructure, an indication of Fröhlich polaron formation due to forward-scattering electron−phonon coupling. Parabolic fitting of the h-BN bands yields an effective mass enhancement of ∼2.3, suggesting an intermediate coupling strength. Our theoretical simulations based on Migdal−Eliashberg theory corroborate the experimental results, allowing the extraction of microscopic physical parameters. Moreover, renormalization of graphene π-band is observed due to the hybridization with the h-BN band. Our work generalizes the polaron study from transition metal oxides to van der Waals heterostructures with higher material flexibility, highlighting interlayer coupling as an extra degree of freedom to explore emergent phenomena.
