Rafael Vila

All Publications

• LiH formation and its impact on Li batteries revealed by cryogenic electron microscopy. Science advances Vilá, R. A., Boyle, D. T., Dai, A., Zhang, W., Sayavong, P., Ye, Y., Yang, Y., Dionne, J. A., Cui, Y. 2023; 9 (12): eadf3609

  Abstract

  Little is known about how evolved hydrogen affects the cycling of Li batteries. Hypotheses include the formation of LiH in the solid-electrolyte interphase (SEI) and dendritic growth of LiH. Here, we discover that LiH formation in Li batteries likely follows a different pathway: Hydrogen evolved during cycling reacts to nucleate and grow LiH within already deposited Li metal, consuming active Li. We provide the evidence that LiH formed in Li batteries electrically isolates active Li from the current collector that degrades battery capacity. We detect the coexistence of Li metal and LiH also on graphite and silicon anodes, showing that LiH forms in most Li battery anode chemistries. Last, we find that LiH has its own SEI layer that is chemically and structurally distinct from the SEI on Li metal. Our results highlight the formation mechanism and chemical origins of LiH, providing critical insight into how to prevent its formation.

  View details for DOI 10.1126/sciadv.adf3609

  View details for PubMedID 36961896

• Ni Anchored to Hydrogen-Substituted Graphdiyne for Lithium Sulfide Cathodes in Lithium-Sulfur Batteries. Nano letters Greenburg, L. C., Gao, X., Zhang, P., Zheng, X., Wang, J., Vila, R. A., Cui, Y. 2023

  Abstract

  Lithium-sulfur (Li-S) batteries are promising candidates for next-generation energy storage systems due to their high theoretical energy density and the low cost of sulfur. However, slow conversion kinetics between the insulating S and lithium sulfide (Li2S) remains as a technical challenge. In this work, we report a catalyst featuring nickel (Ni) single atoms and clusters anchored to a porous hydrogen-substituted graphdiyne support (termed Ni@HGDY), which is incorporated in Li2S cathodes. The rapidly synthesized catalyst was found to enhance ionic and electronic conductivity, decrease the reaction overpotential, and promote more complete conversion between Li2S and sulfur. The addition of Ni@HGDY to commercial Li2S powder enabled a capacity of over 516 mAh gLi2S-1 at 1 C for over 125 cycles, whereas the control Li2S cathode managed to maintain just over 200 mAh gLi2S-1. These findings highlight the efficacy of Ni as a metal catalyst and demonstrate the promise of HGDY in energy storage devices.

  View details for DOI 10.1021/acs.nanolett.3c01034

  View details for PubMedID 37350461

• In Situ Prelithiation by Direct Integration of Lithium Mesh into Battery Cells. Nano letters Yang, Y., Wang, J., Kim, S. C., Zhang, W., Peng, Y., Zhang, P., Vila, R. A., Ma, Y., Jeong, Y. K., Cui, Y. 2023

  Abstract

  Silicon (Si)-based anodes are promising for next-generation lithium (Li)-ion batteries due to their high theoretical capacity (3600 mAh/g). However, they suffer quantities of capacity loss in the first cycle from initial solid electrolyte interphase (SEI) formation. Here, we present an in situ prelithiation method to directly integrate a Li metal mesh into the cell assembly. A series of Li meshes are designed as prelithiation reagents, which are applied to the Si anode in battery fabrication and spontaneously prelithiate Si with electrolyte addition. Various porosities of Li meshes tune prelithiation amounts to control the degree of prelithiation precisely. Besides, the patterned mesh design enhances the uniformity of prelithiation. With an optimized prelithiation amount, the in situ prelithiated Si-based full cell shows a constant >30% capacity improvement in 150 cycles. This work presents a facile prelithiation approach to improve battery performance.

  View details for DOI 10.1021/acs.nanolett.3c00859

  View details for PubMedID 37236151

• Dissolution of the Solid Electrolyte Interphase and Its Effects on Lithium Metal Anode Cyclability. Journal of the American Chemical Society Sayavong, P., Zhang, W., Oyakhire, S. T., Boyle, D. T., Chen, Y., Kim, S. C., Vilá, R. A., Holmes, S. E., Kim, M. S., Bent, S. F., Bao, Z., Cui, Y. 2023

  Abstract

  At >95% Coulombic efficiencies, most of the capacity loss for Li metal anodes (LMAs) is through the formation and growth of the solid electrolyte interphase (SEI). However, the mechanism through which this happens remains unclear. One property of the SEI that directly affects its formation and growth is the SEI's solubility in the electrolyte. Here, we systematically quantify and compare the solubility of SEIs derived from ether-based electrolytes optimized for LMAs using in-operando electrochemical quartz crystal microbalance (EQCM). A correlation among solubility, passivity, and cyclability established in this work reveals that SEI dissolution is a major contributor to the differences in passivity and electrochemical performance among battery electrolytes. Together with our EQCM, X-ray photoelectron spectroscopy (XPS), and nuclear magnetic resonance (NMR) spectroscopy results, we show that solubility depends on not only the SEI's composition but also the properties of the electrolyte. This provides a crucial piece of information that could help minimize capacity loss due to SEI formation and growth during battery cycling and aging.

  View details for DOI 10.1021/jacs.3c03195

  View details for PubMedID 37220230

• Hydrogen-substituted graphdiyne-assisted ultrafast sparking synthesis of metastable nanomaterials. Nature nanotechnology Zheng, X., Gao, X., Vila, R. A., Jiang, Y., Wang, J., Xu, R., Zhang, R., Xiao, X., Zhang, P., Greenburg, L. C., Yang, Y., Xin, H. L., Zheng, X., Cui, Y. 2022

  Abstract

  Metastable nanomaterials, such as single-atom and high-entropy systems, with exciting physical and chemical properties are increasingly important for next-generation technologies. Here, we developed a hydrogen-substituted graphdiyne-assisted ultrafast sparking synthesis (GAUSS) platform for the preparation of metastable nanomaterials. The GAUSS platform can reach an ultra-high reaction temperature of 3,286K within 8ms, a rate exceeding 105Ks-1. Controlling the composition and chemistry of the hydrogen-substituted graphdiyne aerogel framework, the reaction temperature can be tuned from 1,640 K to 3,286K. We demonstrate the versatility of the GAUSS platform with the successful synthesis of single atoms, high-entropy alloys and high-entropy oxides. Electrochemical measurements and density functional theory show that single atoms synthesized by GAUSS enhance the lithium-sulfur redox reaction kinetics in all-solid-state lithium-sulfur batteries. Our design of the GAUSS platform offers a powerful way to synthesize a variety of metastable nanomaterials.

  View details for DOI 10.1038/s41565-022-01272-4

  View details for PubMedID 36585516

• Onboard early detection and mitigation of lithium plating in fast-charging batteries. Nature communications Huang, W., Ye, Y., Chen, H., Vilá, R. A., Xiang, A., Wang, H., Liu, F., Yu, Z., Xu, J., Zhang, Z., Xu, R., Wu, Y., Chou, L. Y., Wang, H., Xu, J., Boyle, D. T., Li, Y., Cui, Y. 2022; 13 (1): 7091

  Abstract

  Fast-charging is considered as one of the most desired features needed for lithium-ion batteries to accelerate the mainstream adoption of electric vehicles. However, current battery charging protocols mainly consist of conservative rate steps to avoid potential hazardous lithium plating and its associated parasitic reactions. A highly sensitive onboard detection method could enable battery fast-charging without reaching the lithium plating regime. Here, we demonstrate a novel differential pressure sensing method to precisely detect the lithium plating event. By measuring the real-time change of cell pressure per unit of charge (dP/dQ) and comparing it with the threshold defined by the maximum of dP/dQ during lithium-ion intercalation into the negative electrode, the onset of lithium plating before its extensive growth can be detected with high precision. In addition, we show that by integrating this differential pressure sensing into the battery management system (BMS), a dynamic self-regulated charging protocol can be realized to effectively extinguish the lithium plating triggered by low temperature (0 °C) while the conventional static charging protocol leads to catastrophic lithium plating at the same condition. We propose that differential pressure sensing could serve as an early nondestructive diagnosis method to guide the development of fast-charging battery technologies.

  View details for DOI 10.1038/s41467-022-33486-4

  View details for PubMedID 36402759

• Correlating Kinetics to Cyclability Reveals Thermodynamic Origin of Lithium Anode Morphology in Liquid Electrolytes. Journal of the American Chemical Society Boyle, D. T., Kim, S. C., Oyakhire, S. T., Vila, R. A., Huang, Z., Sayavong, P., Qin, J., Bao, Z., Cui, Y. 2022

  Abstract

  The rechargeability of lithium metal batteries strongly depends on the electrolyte. The uniformity of the electroplated Li anode morphology underlies this dependence, so understanding the main drivers of uniform plating is critical for further electrolyte discovery. Here, we correlate electroplating kinetics with cyclability across several classes of electrolytes to reveal the mechanistic influence electrolytes have on morphology. Fast charge-transfer kinetics at fresh Li-electrolyte interfaces correlate well with uniform morphology and cyclability, whereas the resistance of Li+ transport through the solid electrolyte interphase (SEI) weakly correlates with cyclability. These trends contrast with the conventional thought that Li+ transport through the electrolyte or SEI is the main driver of morphological differences between classes of electrolytes. Relating these trends to Li+ solvation, Li nucleation, and the charge-transfer mechanism instead suggests that the Li/Li+ equilibrium potential and the surface energy─thermodynamic factors modulated by the strength of Li+ solvation─underlie electrolyte-dependent trends of Li morphology. Overall, this work provides an insight for discovering functional electrolytes, tuning kinetics in batteries, and explaining why weakly solvating fluorinated electrolytes favor uniform Li plating.

  View details for DOI 10.1021/jacs.2c08182

  View details for PubMedID 36318744

• Resolving Current-Dependent Regimes of Electroplating Mechanisms for Fast Charging Lithium Metal Anodes. Nano letters Boyle, D. T., Li, Y., Pei, A., Vila, R. A., Zhang, Z., Sayavong, P., Kim, M. S., Huang, W., Wang, H., Liu, Y., Xu, R., Sinclair, R., Qin, J., Bao, Z., Cui, Y. 2022

  Abstract

  Poor fast-charge capabilities limit the usage of rechargeable Li metal anodes. Understanding the connection between charging rate, electroplating mechanism, and Li morphology could enable fast-charging solutions. Here, we develop a combined electroanalytical and nanoscale characterization approach to resolve the current-dependent regimes of Li plating mechanisms and morphology. Measurement of Li+ transport through the solid electrolyte interphase (SEI) shows that low currents induce plating at buried Li||SEI interfaces, but high currents initiate SEI-breakdown and plating at fresh Li||electrolyte interfaces. The latter pathway can induce uniform growth of {110}-faceted Li at extremely high currents, suggesting ion-transport limitations alone are insufficient to predict Li morphology. At battery relevant fast-charging rates, SEI-breakdown above a critical current density produces detrimental morphology and poor cyclability. Thus, prevention of both SEI-breakdown and slow ion-transport in the electrolyte is essential. This mechanistic insight can inform further electrolyte engineering and customization of fast-charging protocols for Li metal batteries.

  View details for DOI 10.1021/acs.nanolett.2c02792

  View details for PubMedID 36214378

• Bright and stable light-emitting diodes made with perovskite nanocrystals stabilized in metal-organic frameworks NATURE PHOTONICS Tsai, H., Shrestha, S., Vila, R. A., Huang, W., Liu, C., Hou, C., Huang, H., Wen, X., Li, M., Wiederrecht, G., Cui, Y., Cotlet, M., Zhang, X., Ma, X., Nie, W. 2021

  View details for DOI 10.1038/s41566-021-00857-0

  View details for Web of Science ID 000692990800001

• Cryogenic Electron Microscopy for Energy Materials. Accounts of chemical research Zhang, Z., Cui, Y., Vila, R., Li, Y., Zhang, W., Zhou, W., Chiu, W., Cui, Y. 2021

  Abstract

  ConspectusThe development of clean energy generation, transmission, and distribution technology, for example, high energy density batteries and high efficiency solar cells, is critical to the progress toward a sustainable future. Such advancement in both scientific understanding and technological innovations entail an atomic- and molecular-resolution understanding of the key materials and fundamental processes governing the operation and failure of the systems. These dynamic processes span multiple length and time scales bridging materials and interfaces involved across the entire device architecture. However, these key components are often highly sensitive to air, moisture, and electron-beam radiation and therefore remain resistant to conventional nanoscale interrogation by electron-optical methods, such as high-resolution (scanning) transmission electron microscopy and spectroscopy.Fortunately, the rapid progress in cryogenic electron microscopy (cryo-EM) for physical sciences starts to offer researchers new tools and methods to probe these otherwise inaccessible length scales of components and phenomena in energy science. Specifically, weakly bonded and reactive materials, interfaces and phases that typically degrade under high energy electron-beam irradiation and environmental exposure can potentially be protected and stabilized by cryogenic methods, bringing up thrilling opportunities to address many crucial yet unanswered questions in energy science, which can eventually lead to new scientific discoveries and technological breakthroughs.Thus, in this Account, we aim to highlight the significance of cryo-EM to energy related research and the impactful results that can be potentially spawned from there. Due to the limited space, we will mainly review representative examples of cryo-EM methodology for lithium (Li)-based batteries, hybrid perovskite solar cells, and metal-organic-frameworks, which have shown great promise in revealing atomic resolution of both structural and chemical information on the sensitive yet critical components in these systems. We will first emphasize the application of cryo-EM to resolve the nanostructure and chemistry of solid-electrolyte interphases, cathode-electrolyte interphase, and electrode materials in batteries to reflect how cryo-EM could inspire rational materials design and guide battery research toward practical applications. We then discuss how cryo-EM helped to reveal guest intercalation chemistry in weakly bonded metal-organic-frameworks to develop a complete picture of host-guest interaction. Next, we summarize efforts in hybrid perovskite materials for solar cells where cryo-EM preserved the volatile organic molecules and protected perovskites from any air or moisture contamination. Finally, we conclude with perspectives and brief discussion on future directions for cryo-EM in energy and materials science.

  View details for DOI 10.1021/acs.accounts.1c00183

  View details for PubMedID 34278783

• Potentiometric Measurement to Probe Solvation Energy and Its Correlation to Lithium Battery Cyclability. Journal of the American Chemical Society Kim, S. C., Kong, X., Vila, R. A., Huang, W., Chen, Y., Boyle, D. T., Yu, Z., Wang, H., Bao, Z., Qin, J., Cui, Y. 2021

  Abstract

  The electrolyte plays a critical role in lithium-ion batteries, as it impacts almost every facet of a battery's performance. However, our understanding of the electrolyte, especially solvation of Li+, lags behind its significance. In this work, we introduce a potentiometric technique to probe the relative solvation energy of Li+ in battery electrolytes. By measuring open circuit potential in a cell with symmetric electrodes and asymmetric electrolytes, we quantitatively characterize the effects of concentration, anions, and solvents on solvation energy across varied electrolytes. Using the technique, we establish a correlation between cell potential (Ecell) and cyclability of high-performance electrolytes for lithium metal anodes, where we find that solvents with more negative cell potentials and positive solvation energies-those weakly binding to Li+-lead to improved cycling stability. Cryogenic electron microscopy reveals that weaker solvation leads to an anion-derived solid-electrolyte interphase that stabilizes cycling. Using the potentiometric measurement for characterizing electrolytes, we establish a correlation that can guide the engineering of effective electrolytes for the lithium metal anode.

  View details for DOI 10.1021/jacs.1c03868

  View details for PubMedID 34184873

• Microclusters of Kinked Silicon Nanowires Synthesized by a Recyclable Iodide Process for High-Performance Lithium-Ion Battery Anodes ADVANCED ENERGY MATERIALS Jeong, Y., Huang, W., Vila, R. A., Huang, W., Wang, J., Kim, S., Kim, Y., Zhao, J., Cui, Y. 2020

  View details for DOI 10.1002/aenm.202002108

  View details for Web of Science ID 000573081400001

• Nickel Impurities in the Solid-Electrolyte Interphase of Lithium-Metal Anodes Revealed by Cryogenic Electron Microscopy CELL REPORTS PHYSICAL SCIENCE Vila, R. A., Huang, W., Cui, Y. 2020; 1 (9)

  View details for DOI 10.1016/j.xcrp.2020.100188

  View details for Web of Science ID 000658752300015

• Incorporating the nanoscale encapsulation concept from liquid electrolytes into solid-state lithium-sulfur batteries. Nano letters Gao, X., Zheng, X., Wang, J., Zhang, Z., Xiao, X., Wan, J., Ye, Y., Chou, L., Lee, H. K., Wang, J., Vila, R. A., Yang, Y., Zhang, P., Wang, L., Cui, Y. 2020

  Abstract

  Lithium-sulfur (Li-S) batteries are attractive due to their high specific energy and low-cost prospect. Most studies in the past decade are based on these batteries with liquid electrolytes, where many exciting material/structural designs are realized at the nanoscale to address problems of Li-S chemistry. Recently, there is a new promising direction to develop Li-S batteries with solid polymer electrolytes, although 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 very effective in solid polymer electrolytes. Using in situ optical cell measurement and sulfur K-edge X-ray absorption near edge spectroscopy, we find that polysulfides form and are well trapped 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, proved by both experiments and density functional theory calculations. A high cell-level specific energy of 427 W∙h∙kg-1 at 60 °C (including the mass of the anode, cathode, and solid-state electrolyte, but excluding the current collector and packaging) is achieved by integrating TiS2 encapsulated Li2S cathode with ultrathin polyethylene oxide-based solid polymer electrolyte (10~20 m) and lithium metal anode. The solid-state cells show excellent stability over 150 charge/discharge cycles at 0.8 C at 80 °C. This study points to the fruitful direction of borrowing concepts from liquid electrolytes into solid-state Li-S batteries.

  View details for DOI 10.1021/acs.nanolett.0c02033

  View details for PubMedID 32515973

• Tortuosity Effects in Lithium-Metal Host Anodes JOULE Chen, H., Pei, A., Wan, J., Lin, D., Vila, R., Wang, H., Mackanic, D., Steinruck, H., Huang, W., Li, Y., Yang, A., Xie, J., Wu, Y., Wang, H., Cui, Y. 2020; 4 (4): 938–52

  View details for DOI 10.1016/j.joule.2020.03.008

  View details for Web of Science ID 000527264500022

• Electrochemical generation of liquid and solid sulfur on two-dimensional layered materials with distinct areal capacities. Nature nanotechnology Yang, A. n., Zhou, G. n., Kong, X. n., Vilá, R. A., Pei, A. n., Wu, Y. n., Yu, X. n., Zheng, X. n., Wu, C. L., Liu, B. n., Chen, H. n., Xu, Y. n., Chen, D. n., Li, Y. n., Fakra, S. n., Hwang, H. Y., Qin, J. n., Chu, S. n., Cui, Y. n. 2020

  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.

  View details for DOI 10.1038/s41565-019-0624-6

  View details for PubMedID 31988508

• Electrochemical generation of liquid and solid sulfur on two-dimensional layered materials with distinct areal capacities Nature Nanotechnology Yang, A., Zhou, G., et al 2020

  View details for DOI 10.1038/s41565-019-0624-6

• Unravelling Degradation Mechanisms and Atomic Structure of Organic-Inorganic Halide Perovskites by Cryo-EM JOULE Li, Y., Zhou, W., Li, Y., Huang, W., Zhang, Z., Chen, G., Wang, H., Wu, G., Rolston, N., Vila, R., Chiu, W., Cui, Y. 2019; 3 (11): 2854–66

  View details for DOI 10.1016/j.joule.2019.08.016

  View details for Web of Science ID 000497987900024

• Unravelling Atomic Structure and Degradation Mechanisms of Organic-Inorganic Halide Perovskites by Cryo-EM. Joule Li, Y., Zhou, W., Li, Y., Huang, W., Zhang, Z., Chen, G., Wang, H., Wu, G. H., Rolston, N., Vila, R., Chiu, W., Cui, Y. 2019; 3 (11): 2854-2866

  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 cryogenic-electron 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.

  View details for DOI 10.1016/j.joule.2019.08.016

  View details for PubMedID 34109301

  View details for PubMedCentralID PMC8186345

• Cryo-EM Structures of Atomic Surfaces and Host-Guest Chemistry in Metal-Organic Frameworks MATTER Li, Y., Wang, K., Zhou, W., Li, Y., Vila, R., Huang, W., Wang, H., Chen, G., Wu, G., Tsao, Y., Wang, H., Sinclair, R., Chiu, W., Cui, Y. 2019; 1 (2): 428–38

  View details for DOI 10.1016/j.matt.2019.06.001

  View details for Web of Science ID 000519688200015

• Cryo-EM structures of atomic surfaces and host-guest chemistry in metal-organic frameworks. Matter Li, Y., Wang, K., Zhou, W., Li, Y., Vila, R., Huang, W., Wang, H., Chen, G., Wu, G. H., Tsao, Y., Wang, H., Sinclair, R., Chiu, W., Cui, Y. 2019; 1 (2): 428-438

  Abstract

  Host-guest interactions govern the chemistry of a broad range of functional materials, but direct imaging using conventional transmission electron microscopy (TEM) has not been possible. This problem is exacerbated in metal-organic framework (MOF) 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 provides insight to its growth behavior. Furthermore, we observe two distinct binding sites for CO2 within the ZIF-8 pore, which are predicted by density functional theory (DFT) 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.

  View details for DOI 10.1016/j.matt.2019.06.001

  View details for PubMedID 34104881

  View details for PubMedCentralID PMC8184120

• Wrinkled Graphene Cages as Hosts for High-Capacity Li Metal Anodes Shown by Cryogenic Electron Microscopy. Nano letters Wang, H., Li, Y., Li, Y., Liu, Y., Lin, D., Zhu, C., Chen, G., Yang, A., Yan, K., Chen, H., Zhu, Y., Li, J., Xie, J., Xu, J., Zhang, Z., Vila, R., Pei, A., Wang, K., Cui, Y. 2019

  Abstract

  Lithium (Li) metal has long been considered the "holy grail" of battery anode chemistry but is plagued by low efficiency and poor safety due to its high chemical reactivity and large volume fluctuation, respectively. Here we introduce a new host of wrinkled graphene cage (WGC) for Li metal. Different from recently reported amorphous carbon spheres, WGC show highly improved mechanical stability, better Li ion conductivity, and excellent solid electrolyte interphase (SEI) for continuous robust Li metal protection. At low areal capacities, Li metal is preferentially deposited inside the graphene cage. Cryogenic electron microscopy characterization shows that a uniform and stable SEI forms on the WGC surface that can shield the Li metal from direct exposure to electrolyte. With increased areal capacities, Li metal is plated densely and homogeneously into the outer pore spaces between graphene cages with no dendrite growth or volume change. As a result, a high Coulombic efficiency (CE) of 98.0% was achieved under 0.5 mA/cm2 and 1-10 mAh/cm2 in commercial carbonate electrolytes, and a CE of 99.1% was realized with high-concentration electrolytes under 0.5 mA/cm2 and 3 mAh/cm2. Full cells using WGC electrodes with prestored Li paired with Li iron phosphate showed greatly improved cycle lifetime. With 10 mAh/cm2 Li metal deposition, the WGC/Li compositeanodewas able to provide a high specific capacity of 2785 mAh/g. With its roll-to-roll compatible fabrication procedure, WGC serves as a highly promising material for the practical realization of Li metal anodes in next-generation high energy density secondary batteries.

  View details for PubMedID 30676759

• In situ crystallization kinetics of two-dimensional MoS2 2D Materials Vilá, R. A., Rao, R., Muratore, C., Bianco, E., Robinson, J. A., Maruyama, B., Glavin, N. R. 2017; 5 (1)

  View details for DOI 10.1088/2053-1583/aa9674

• Bottom-up synthesis of vertically oriented two-dimensional materials 2D MATERIALS Vila, R. A., Momeni, K., Wang, Q., Bersch, B. M., Lu, N., Kim, M. J., Chen, L. Q., Robinson, J. A. 2016; 3 (4)

  View details for DOI 10.1088/2053-1583/3/4/041003

  View details for Web of Science ID 000386050700001

• Two-dimensional gallium nitride realized via graphene encapsulation NATURE MATERIALS Al Balushi, Z. Y., Wang, K., Ghosh, R. K., Vila, R. A., Eichfeld, S. M., Caldwell, J. D., Qin, X., Lin, Y., DeSario, P. A., Stone, G., Subramanian, S., Paul, D. F., Wallace, R. M., Datta, S., Redwing, J. M., Robinson, J. A. 2016; 15 (11): 1166-?

  Abstract

  The spectrum of two-dimensional (2D) and layered materials 'beyond graphene' offers a remarkable platform to study new phenomena in condensed matter physics. Among these materials, layered hexagonal boron nitride (hBN), with its wide bandgap energy (∼5.0-6.0 eV), has clearly established that 2D nitrides are key to advancing 2D devices. A gap, however, remains between the theoretical prediction of 2D nitrides 'beyond hBN' and experimental realization of such structures. Here we demonstrate the synthesis of 2D gallium nitride (GaN) via a migration-enhanced encapsulated growth (MEEG) technique utilizing epitaxial graphene. We theoretically predict and experimentally validate that the atomic structure of 2D GaN grown via MEEG is notably different from reported theory. Moreover, we establish that graphene plays a critical role in stabilizing the direct-bandgap (nearly 5.0 eV), 2D buckled structure. Our results provide a foundation for discovery and stabilization of 2D nitrides that are difficult to prepare via traditional synthesis.

  View details for DOI 10.1038/NMAT4742

  View details for Web of Science ID 000386377000011

  View details for PubMedID 27571451

• Growth and Tunable Surface Wettability of Vertical MoS2 Layers for Improved Hydrogen Evolution Reactions ACS APPLIED MATERIALS & INTERFACES Bhimanapati, G. R., Hankins, T., Lei, Y., Vila, R. A., Fuller, I., Terrones, M., Robinson, J. A. 2016; 8 (34): 22190-22195

  Abstract

  Layered materials, especially the transition metal dichalcogenides (TMDs), are of interest for a broad range of applications. Among the class of TMDs, molybdenum disulfide (MoS2) is perhaps the most studied because of its natural abundance and use in optoelectronics, energy storage and energy conversion applications. Understanding the fundamental structure-property relations is key for tailoring the enhancement in the above-mentioned applications. Here, we report a controlled powder vaporization synthesis of MoS2 flower-like structures consisting of vertically grown layers of MoS2 exhibiting exposed edges. This growth is readily achievable on multiple substrates, such as graphite, silicon, and silicon dioxide. The resulting MoS2 flowers are highly crystalline and stoichiometric. Further observations using contact angle indicate that MoS2 flowers exhibit the highest reported contact angle of ∼160 ± 10°, making the material super hydrophobic. This surface wettability was further tuned by changing the edge chemistry of the MoS2 flowers using an ozone etching treatment. Hydrogen evolution reaction (HER) measurements indicate that the surface treated with UV-ozone showed a reduction in the Tafel slope from 185 to 54 mV/dec, suggesting an increase in the amount of reactive surface to generate hydrogen.

  View details for DOI 10.1021/acsami.6b05848

  View details for Web of Science ID 000382514100041

  View details for PubMedID 27500662