Publications by authors named "Gary W Rubloff"

58 Publications

Atomic Layer Deposition of Sodium Phosphorus Oxynitride: A Conformal Solid-State Sodium-Ion Conductor.

ACS Appl Mater Interfaces 2020 May 1;12(19):21641-21650. Epub 2020 May 1.

Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, United States.

The development of novel materials that are compatible with nanostructured architectures is required to meet the demands of next-generation energy-storage technologies. Atomic layer deposition (ALD) allows for the precise synthesis of new materials that can conformally coat complex 3D structures. In this work, we demonstrate a thermal ALD process for sodium phosphorus oxynitride (NaPON), a thin-film solid-state electrolyte (SSE), for sodium-ion batteries (SIBs). NaPON is analogous to the commonly used lithium phosphorus oxynitride SSE in lithium-ion batteries. The ALD process produces a conformal film with a stoichiometry of NaPON, corresponding to a sodium polyphosphazene structure. The electrochemical properties of NaPON are characterized to evaluate its potential in SIBs. The NaPON film exhibited a high ionic conductivity of 1.0 × 10 S/cm at 25 °C and up to 2.5 × 10 S/cm at 80 °C, with an activation energy of 0.53 eV. In addition, the ionic conductivity is comparable and even higher than the ionic conductivities of ALD-fabricated Li conductors. This promising result makes NaPON a viable SSE or passivation layer in solid-state SIBs.
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http://dx.doi.org/10.1021/acsami.0c03578DOI Listing
May 2020

Enhancing Lithium Insertion with Electrostatic Nanoconfinement in a Lithography Patterned Precision Cell.

ACS Nano 2019 Jul 5;13(7):8481-8489. Epub 2019 Jul 5.

Department of Electrical Engineering , Yale University , New Haven , Connecticut 06511 , United States.

The rapidly growing demand for portable electronics, electric vehicles, and grid storage drives the pursuit of high-performance electrical energy storage (EES). A key strategy for improving EES performance is exploiting nanostructured electrodes that present nanoconfined environments of adjacent electrolytes, with the goal to decrease ion diffusion paths and increase active surface areas. However, fundamental gaps persist in understanding the interface-governed electrochemistry in such nanoconfined geometries, in part because of the imprecise and variable dimension control. Here, we report quantification of lithium insertion under nanoconfinement of the electrolyte in a precise lithography-patterned nanofluidic cell. We show a mechanism that enhances ion insertion under nanoconfinement, namely, selective ion accumulation when the confinement length is comparable to the electrical double layer thickness. The nanofabrication approach with uniform and accurate dimensional control provides a versatile model system to explore fundamental mechanisms of nanoscale electrochemistry, which could have an impact on practical energy storage systems.
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http://dx.doi.org/10.1021/acsnano.9b04390DOI Listing
July 2019

Three-Dimensional Solid-State Lithium-Ion Batteries Fabricated by Conformal Vapor-Phase Chemistry.

ACS Nano 2018 05 26;12(5):4286-4294. Epub 2018 Apr 26.

Materials Physics Department , Sandia National Laboratory , MS9161, 7011 East Ave , Livermore , California 94550 , United States.

Three-dimensional thin-film solid-state batteries (3D TSSB) were proposed by Long et al. in 2004 as a structure-based approach to simultaneously increase energy and power densities. Here, we report experimental realization of fully conformal 3D TSSBs, demonstrating the simultaneous power-and-energy benefits of 3D structuring. All active battery components-electrodes, solid electrolyte, and current collectors-were deposited by atomic layer deposition (ALD) onto standard CMOS processable silicon wafers microfabricated to form arrays of deep pores with aspect ratios up to approximately 10. The cells utilize an electrochemically prelithiated LiVO cathode, a very thin (40-100 nm) LiPON solid electrolyte, and a SnN anode. The fabrication process occurs entirely at or below 250 °C, promising compatibility with a variety of substrates as well as integrated circuits. The multilayer battery structure enabled all-ALD solid-state cells to deliver 37 μAh/cm·μm (normalized to cathode thickness) with only 0.02% per-cycle capacity loss. Conformal fabrication of full cells over 3D substrates increased the areal discharge capacity by an order of magnitude while simulteneously improving power performance, a trend consistent with a finite element model. This work shows that the exceptional conformality of ALD, combined with conventional semiconductor fabrication methods, provides an avenue for the successful realization of long-sought 3D TSSBs which provide power performance scaling in regimes inaccessible to planar form factor cells.
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http://dx.doi.org/10.1021/acsnano.7b08751DOI Listing
May 2018

Kinetics-Controlled Degradation Reactions at Crystalline LiPON/Li CoO and Crystalline LiPON/Li-Metal Interfaces.

ChemSusChem 2018 Jun 18;11(12):1956-1969. Epub 2018 Apr 18.

Sandia National Laboratories, MS 1415, Albuquerque, NM 87185, USA.

Detailed understanding of solid-solid interface structure-function relationships is critical for the improvement and wide deployment of all-solid-state batteries. The interfaces between lithium phosphorous oxynitride (LiPON) solid electrolyte material and lithium metal anode, and between LiPON and Li CoO cathode, have been reported to generate solid-electrolyte interphase (SEI)-like products and/or disordered regions. Using electronic structure calculations and crystalline LiPON models, we predict that LiPON models with purely P-N-P backbones are kinetically inert towards lithium at room temperature. In contrast, transfer of oxygen atoms from low-energy Li CoO (104) surfaces to LiPON is much faster under ambient conditions. The mechanisms of the primary reaction steps, LiPON structural motifs that readily reacts with lithium metal, experimental results on amorphous LiPON to partially corroborate these predictions, and possible mitigation strategies to reduce degradations are discussed. LiPON interfaces are found to be useful case studies for highlighting the importance of kinetics-controlled processes during battery assembly at moderate processing temperatures.
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http://dx.doi.org/10.1002/cssc.201800027DOI Listing
June 2018

Nanoscale Protection Layers To Mitigate Degradation in High-Energy Electrochemical Energy Storage Systems.

Acc Chem Res 2018 01 2;51(1):97-106. Epub 2018 Jan 2.

Department of Materials Science and Engineering, University of Maryland , College Park, Maryland 20742, United States.

In the pursuit of energy storage devices with higher energy and power, new ion storage materials and high-voltage battery chemistries are of paramount importance. However, they invite-and often enhance-degradation mechanisms, which are reflected in capacity loss with charge/discharge cycling and sometimes in safety problems. Degradation mechanisms are often driven by fundamentals such as chemical and electrochemical reactions at electrode-electrolyte interfaces, volume expansion and stress associated with ion insertion and extraction, and profound inhomogeneity of electrochemical behavior. While it is important to identify and understand these mechanisms at some reasonable level, it is even more critical to design strategies to mitigate these degradation pathways and to develop means to implement and validate the strategies. A growing set of research highlights the mitigation benefits achievable by forming thin protection layers (PLs) intentionally created as artificial interphase regions at the electrode-electrolyte interface. These advances illustrate a promising-perhaps even generic-pathway for enabling higher-energy and higher-voltage battery configurations. In this Account, we summarize examples of such PLs that serve as mitigation strategies to avoid degradation in lithium metal anodes, conversion-type electrode materials, and alloy-type electrodes. Examples are chosen from a larger body of electrochemical degradation research carried out in Nanostructures for Electrical Energy Storage (NEES), our DOE Energy Frontier Research Center. Overall, we argue on the basis of experimental and theoretical evidence that PLs effectively stabilize the electrochemical interfaces to prevent parasitic chemical and electrochemical reactions and mitigate the structural, mechanical, and compositional degradation of the electrode materials at the electrode-electrolyte interfaces. The evidenced improvement in performance metrics is accomplished by (1) establishing a homogeneous interface for ion insertion and extraction, (2) providing mechanical constraints to maintain structural integrity and robust electronic and ionic conduction pathways, and (3) introducing spatial confinements on the electrode material matrix to alter the phase transformation (delaying the occurrence of the conversion reaction) upon Li insertion, which results in superior electrode performance, excellent capacity retention, and improved reversibility. Taken together, these examples portray a valuable role for thin protection layers synthesized over electrode surfaces, both for their benefit to cycle stability and for revealing insights into degradation and mitigation mechanisms. Furthermore, they underscore the impact of complex electrochemical behavior at nanoscale materials and nanostructure interfaces in modulating the behavior of energy storage devices at the mesoscale and macroscale.
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http://dx.doi.org/10.1021/acs.accounts.7b00524DOI Listing
January 2018

High performance asymmetric VO-SnO nanopore battery by atomic layer deposition.

Nanoscale 2017 Aug;9(32):11566-11573

Lam Research Corp, Tualatin, OR 97062, USA.

Here we report the high performance and cyclability of an asymmetric full cell nanopore battery, comprised of VO as the cathode and prelithiated SnO as the anode, with integrated nanotubular Pt current collectors underneath each nanotubular storage electrode, confined within an anodized aluminium oxide (AAO) nanopore. Enabled by atomic layer deposition (ALD), this coaxial nanotube full cell is fully confined within a high aspect ratio nanopore (150 nm in diameter, 50 μm in length), with an ultra-small volume of about 1 fL. By controlling the amount of lithium ion prelithiated into the SnO anode, we can tune the full cell output voltage in the range of 0.3 V to 3 V. When tested as a massively parallel device (∼2 billion cm), this asymmetric nanopore battery array displays exceptional rate performance and cyclability: when cycled between 1 V and 3 V, capacity retention at the 200C rate is ∼73% of that at 1C, and at 25C rate only 2% capacity loss occurs after more than 500 charge/discharge cycles. With the increased full cell output potential, the asymmetric VO-SnO nanopore battery shows significantly improved energy and power density over the previously reported symmetric cell, 4.6 times higher volumetric energy and 5.2 times higher power density - an even more promising indication that controlled nanostructure designs employing nanoconfined environments with large electrode surface areas present promising directions for future battery technology.
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http://dx.doi.org/10.1039/c7nr02151hDOI Listing
August 2017

Perspectives in flow-based microfluidic gradient generators for characterizing bacterial chemotaxis.

Biomicrofluidics 2016 Nov 10;10(6):061301. Epub 2016 Nov 10.

Department of Mechanical Engineering, The Catholic University of America , Washington, DC 20064, USA.

Chemotaxis is a phenomenon which enables cells to sense concentrations of certain chemical species in their microenvironment and move towards chemically favorable regions. Recent advances in microbiology have engineered the chemotactic properties of bacteria to perform novel functions, but traditional methods of characterizing chemotaxis do not fully capture the associated cell motion, making it difficult to infer mechanisms that link the motion to the microbiology which induces it. Microfluidics offers a potential solution in the form of gradient generators. Many of the gradient generators studied to date for this application are flow-based, where a chemical species diffuses across the laminar flow interface between two solutions moving through a microchannel. Despite significant research efforts, flow-based gradient generators have achieved mixed success at accurately capturing the highly subtle chemotactic responses exhibited by bacteria. Here we present an analysis encompassing previously published versions of flow-based gradient generators, the theories that govern their gradient-generating properties, and new, more practical considerations that result from experimental factors. We conclude that flow-based gradient generators present a challenge inherent to their design in that the residence time and gradient decay must be finely balanced, and that this significantly narrows the window for reliable observation and quantification of chemotactic motion. This challenge is compounded by the effects of shear on an ellipsoidal bacterium that causes it to preferentially align with the direction of flow and subsequently suppresses the cross-flow chemotactic response. These problems suggest that a static, non-flowing gradient generator may be a more suitable platform for chemotaxis studies in the long run, despite posing greater difficulties in design and fabrication.
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http://dx.doi.org/10.1063/1.4967777DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5106431PMC
November 2016

Interconnected mesoporous VO electrode: impact on lithium ion insertion rate.

Phys Chem Chem Phys 2016 Nov;18(44):30605-30611

Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland, USA.

Here we introduce a strategy for creating nanotube array electrodes which feature periodic regions of porous interconnections providing open pathways between adjacent nanotubes within the array, utilizing a combination of anodized aluminum oxide growth modification (AAO) and atomic layer deposition. These porous interconnected structures can then be used as testbed electrodes to explore the influence of mesoscale structure on the electrochemical properties of the interconnected mesoporous electrodes. Critically, these unique structures allow the solid state lithium diffusion pathways to be held essentially constant, while the larger structure is modified. While it was anticipated that this strategy would simply provide increased mass loading, the kinetics of the Li ion insertion reaction in the porous interconnected electrodes are dramatically improved, demonstrating significantly better capacity retention at high rates than their aligned counterparts. We utilize a charge deconvolution method to explore the kinetics of the charge storage reactions. We are able to trace the origin of the structural influence on rate performance to electronic effects within the electrodes.
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http://dx.doi.org/10.1039/c6cp05640gDOI Listing
November 2016

Electrochemical Thin Layers in Nanostructures for Energy Storage.

Acc Chem Res 2016 10 16;49(10):2336-2346. Epub 2016 Sep 16.

Department of Materials Science & Engineering, University of Maryland , College Park, Maryland 20742, United States.

Conventional electrical energy storage (EES) electrodes, such as rechargeable batteries, are mostly based on composites of monolithic micrometer sized particles bound together with polymeric and conductive carbon additives and binders. The kinetic limitations of these monolithic chunks of material are inherently linked to their electrical properties, the kinetics of ion insertion through their interface and ion migration in and through the composite phase. Redox chemistry of nanostructured materials in EES systems offer vast gains in power and energy. Furthermore, due to their thin nature, ion and electron transport is dramatically increased, especially when thin heterogeneous conducting layers are employed synergistically. However, since the stability of the electrode material is dictated by the nature of the electrochemical reaction and the accompanying volumetric and interfacial changes from the perspective of overall system lifetime, research with nanostructured materials has shown often indefinite conclusions: in some cases, an increase in unwanted side-reactions due to the high surface area (bad). In other cases, results have shown significantly better handling of mechanical stress that results from lithiation/delithiation (good). Despite these mixed results, scientifically informed design of thin electrode materials, with carefully chosen architectures, is considered a promising route to address many limitations witnessed in EES systems by reducing and protecting electrodes from parasitic reactions, accommodating mechanical stress due to volumetric changes from electrochemical reactions, and optimizing charge carrier mobilities from both the "ionic" and "electronic" points of view. Furthermore, precise nanoscale control over the electrode structure can enable accurate measurement through advanced spectroscopy and microscopy techniques. This Account summarizes recent findings related to thin electrode materials synthesized by atomic layer deposition (ALD) and electrochemical deposition (ECD), including nanowires, nanotubes, and thin films. Throughout the Account, we will show how these techniques enabled us to synthesize electrodes of interest with precise control over the structure and composition of the material. We will illustrate and discuss how the electrochemical response of thin electrodes made by these techniques can facilitate new mechanisms for ion storage, mediate the interfacial electrochemical response of the electrode, and address issues related to electrode degradation over time. The effects of nanosizing materials and their electrochemical response will be mechanistically reviewed through two categories of ion storage: (1) pseudocapacitance and (2) ion insertion. Additionally, we will show how electrochemical processes that are more complicated because of accompanying volumetric changes and electrode degradation pathways can be mediated and controlled by application of thin functional materials on the electrochemically active interface; examples include conversion electrodes, reactive lithium metal anodes, and complex reactions in a Li/O cathode system. The goal of this Account is to illustrate how careful design of thin materials either as active electrodes or as mediating layers can facilitate desirable interfacial electrochemical activity and resolve or shed light on mechanistic limitations of electrochemical processes related to micrometer size particles currently used in energy storage electrodes.
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http://dx.doi.org/10.1021/acs.accounts.6b00315DOI Listing
October 2016

A Rechargeable Al/S Battery with an Ionic-Liquid Electrolyte.

Angew Chem Int Ed Engl 2016 08 15;55(34):9898-901. Epub 2016 Jul 15.

Department of Chemical and Bimolecular Engineering, University of Maryland, College Park, MD, 20740, USA.

Aluminum metal is a promising anode material for next generation rechargeable batteries owing to its abundance, potentially dendrite-free deposition, and high capacity. The rechargeable aluminum/sulfur (Al/S) battery is of great interest owing to its high energy density (1340 Wh kg(-1) ) and low cost. However, Al/S chemistry suffers poor reversibility owing to the difficulty of oxidizing AlSx . Herein, we demonstrate the first reversible Al/S battery in ionic-liquid electrolyte with an activated carbon cloth/sulfur composite cathode. Electrochemical, spectroscopic, and microscopic results suggest that sulfur undergoes a solid-state conversion reaction in the electrolyte. Kinetics analysis identifies that the slow solid-state sulfur conversion reaction causes large voltage hysteresis and limits the energy efficiency of the system.
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http://dx.doi.org/10.1002/anie.201603531DOI Listing
August 2016

The reaction current distribution in battery electrode materials revealed by XPS-based state-of-charge mapping.

Phys Chem Chem Phys 2016 Jul 30;18(28):19093-102. Epub 2016 Jun 30.

Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA.

Morphologically complex electrochemical systems such as composite or nanostructured lithium ion battery electrodes exhibit spatially inhomogeneous internal current distributions, particularly when driven at high total currents, due to resistances in the electrodes and electrolyte, distributions of diffusion path lengths, and nonlinear current-voltage characteristics. Measuring and controlling these distributions is interesting from both an engineering standpoint, as nonhomogenous currents lead to lower utilization of electrode material, as well as from a fundamental standpoint, as comparisons between theory and experiment are relatively scarce. Here we describe a new approach using a deliberately simple model battery electrode to examine the current distribution in a electrode material limited by poor electronic conductivity. We utilize quantitative spatially resolved X-ray photoelectron spectroscopy to measure the spatial distribution of the state-of-charge of a V2O5 model electrode as a proxy measure for the current distribution on electrodes discharged at varying current densities. We show that the current at the electrode-electrolyte interface falls off with distance from the current collector, and that the current distribution is a strong function of total current. We compare the observed distributions with a simple analytical model which reproduces the dependence of the distribution on total current, but fails to predict the correct length scale. A more complete numerical simulation suggests that dynamic changes in the electronic conductivity of the V2O5 concurrent with lithium insertion may contribute to the differences between theory and experiment. Our observations should help inform design criteria for future electrode architectures.
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http://dx.doi.org/10.1039/c6cp03271kDOI Listing
July 2016

Solid Electrolyte Lithium Phosphous Oxynitride as a Protective Nanocladding Layer for 3D High-Capacity Conversion Electrodes.

ACS Nano 2016 Feb 2;10(2):2693-701. Epub 2016 Feb 2.

Department of Materials Science and Engineering, ‡Institute for Systems Research, and §Department of Chemistry, University of Maryland , College Park, Maryland 20742, United States.

Materials that undergo conversion reactions to form different materials upon lithiation typically offer high specific capacity for energy storage applications such as Li ion batteries. However, since the reaction products often involve complex mixtures of electrically insulating and conducting particles and significant changes in volume and phase, the reversibility of conversion reactions is poor, preventing their use in rechargeable (secondary) batteries. In this paper, we fabricate and protect 3D conversion electrodes by first coating multiwalled carbon nanotubes (MWCNT) with a model conversion material, RuO2, and subsequently protecting them with conformal thin-film lithium phosphous oxynitride (LiPON), a well-known solid-state electrolyte. Atomic layer deposition is used to deposit the RuO2 and the LiPON, thus forming core double-shell MWCNT@RuO2@LiPON electrodes as a model system. We find that the LiPON protection layer enhances cyclability of the conversion electrode, which we attribute to two factors. (1) The LiPON layer provides high Li ion conductivity at the interface between the electrolyte and the electrode. (2) By constraining the electrode materials mechanically, the LiPON protection layer ensures electronic connectivity and thus conductivity during lithiation/delithiation cycles. These two mechanisms are striking in their ability to preserve capacity despite the profound changes in structure and composition intrinsic to conversion electrode materials. This LiPON-protected structure exhibits superior cycling stability and reversibility as well as decreased overpotentials compared to the unprotected core-shell structure. Furthermore, even at very low lithiation potential (0.05 V), the LiPON-protected electrode largely reduces the formation of a solid electrolyte interphase.
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http://dx.doi.org/10.1021/acsnano.5b07757DOI Listing
February 2016

Protocols for Evaluating and Reporting Li-O2 Cell Performance.

J Phys Chem Lett 2016 Jan;7(2):211-5

Department of Chemistry and Biochemistry and †Department of Materials Science and Engineering, University of Maryland , College Park, Maryland 20742, United States.

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http://dx.doi.org/10.1021/acs.jpclett.5b02613DOI Listing
January 2016

Enhancing the reversibility of Mg/S battery chemistry through Li(+) mediation.

J Am Chem Soc 2015 Sep 22;137(38):12388-93. Epub 2015 Sep 22.

Electrochemistry Branch, Power and Energy Division Sensor and Electron Devices Directorate, U.S. Army Research Laboratory , Adelphi, Maryland 20783, United States.

Mg metal is a promising anode material for next generation rechargeable battery due to its dendrite-free deposition and high capacity. However, the best cathode for rechargeable Mg battery was based on high molecular weight MgxMo3S4, thus rendering full cell energetically uncompetitive. To increase energy density, high capacity cathode material like sulfur is proposed. However, to date, only limited work has been reported on Mg/S system, all plagued by poor reversibility attributed to the formation of electrochemically inactive MgSx species. Here, we report a new strategy, based on the effect of Li(+) in activating MgSx species, to conjugate a dendrite-free Mg anode with a reversible polysulfide cathode and present a truly reversible Mg/S battery with capacity up to 1000 mAh/gs for more than 30 cycles. Mechanistic insights supported by spectroscopic and microscopic characterization strongly suggest that the reversibility arises from chemical reactivation of MgSx by Li(+).
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http://dx.doi.org/10.1021/jacs.5b07820DOI Listing
September 2015

Next-Generation Lithium Metal Anode Engineering via Atomic Layer Deposition.

ACS Nano 2015 Jun 21;9(6):5884-92. Epub 2015 May 21.

Lithium metal is considered to be the most promising anode for next-generation batteries due to its high energy density of 3840 mAh g(-1). However, the extreme reactivity of the Li surface can induce parasitic reactions with solvents, contamination, and shuttled active species in the electrolyte, reducing the performance of batteries employing Li metal anodes. One promising solution to this issue is application of thin chemical protection layers to the Li metal surface. Using a custom-made ultrahigh vacuum integrated deposition and characterization system, we demonstrate atomic layer deposition (ALD) of protection layers directly on Li metal with exquisite thickness control. We demonstrate as a proof-of-concept that a 14 nm thick ALD Al2O3 layer can protect the Li surface from corrosion due to atmosphere, sulfur, and electrolyte exposure. Using Li-S battery cells as a test system, we demonstrate an improved capacity retention using ALD-protected anodes over cells assembled with bare Li metal anodes for up to 100 cycles.
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http://dx.doi.org/10.1021/acsnano.5b02166DOI Listing
June 2015

DMSO-Li2O2 Interface in the Rechargeable Li-O2 Battery Cathode: Theoretical and Experimental Perspectives on Stability.

ACS Appl Mater Interfaces 2015 Jun 19;7(21):11402-11. Epub 2015 May 19.

‡Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States.

One of the greatest obstacles for the realization of the nonaqueous Li-O2 battery is finding a solvent that is chemically and electrochemically stable under cell operating conditions. Dimethyl sulfoxide (DMSO) is an attractive candidate for rechargeable Li-O2 battery studies; however, there is still significant controversy regarding its stability on the Li-O2 cathode surface. We performed multiple experiments (in situ XPS, FTIR, Raman, and XRD) which assess the stability of the DMSO-Li2O2 interface and report perspectives on previously published studies. Our electrochemical experiments show long-term stable cycling of a DMSO-based operating Li-O2 cell with a platinum@carbon nanotube core-shell cathode fabricated via atomic layer deposition, specifically with >45 cycles of 40 h of discharge per cycle. This work is complemented by density functional theory calculations of DMSO degradation pathways on Li2O2. Both experimental and theoretical evidence strongly suggests that DMSO is chemically and electrochemically stable on the surface of Li2O2 under the reported operating conditions.
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http://dx.doi.org/10.1021/acsami.5b01969DOI Listing
June 2015

Distal modulation of bacterial cell-cell signalling in a synthetic ecosystem using partitioned microfluidics.

Lab Chip 2015 Apr;15(8):1842-51

Department of Mechanical Engineering, Catholic University of America, Washington, DC 20064, USA.

The human gut is over a meter in length, liquid residence times span several hours. Recapitulating the human gut microbiome "on chip" holds promise to revolutionize therapeutic strategies for a variety of diseases, as well as for maintaining homeostasis in healthy individuals. A more refined understanding of bacterial-bacterial and bacterial-epithelial cell signalling is envisioned and such a device is a key enabler. Indeed, significant advances in the study of bacterial cell-cell signalling have been reported, including at length and time scales of the cells and their responses. Few reports exist, however, where signalling events that span physiologically relevant time scales are monitored and coordinated. Here, we employ principles of biofabrication to assemble, in situ, cell communities that are (i) spatially adjacent within partitioned microchannels for studying near communication and (ii) distally connected within longitudinal microfluidic networks so as to mimic long distance signalling among intestinal flora. We observed native signalling processes of the bacterial quorum sensing autoinducer-2 (AI-2) system among and between these communities. Cells in an upstream device successfully self-reported their activities and also secreted autoinducers that were carried downstream to the assembled networks of bacteria that reported on their presence. Furthermore, active signal modulation of among distal populations was demonstrated in a "programmed" manner where "enhancer" and "reducer" communities were assembled adjacent to the test population or "reporter" cells. The modulator cells either amplified or attenuated the cell-cell signalling between the distal, already communicating cell populations. Modulation was quantified with a bioassay, and the reaction rates of signal production and consumption were further characterized using a first principles mathematical model. Simulated distribution profiles of signalling molecules in the cell-gel composites agreed well with the observed cellular responses. We believe this simple platform and the ease by which it is assembled can be applied to other cell-cell interaction studies among various species or kingdoms of cells within well-regulated microenvironments.
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http://dx.doi.org/10.1039/c5lc00107bDOI Listing
April 2015

Fabrication of 3D core-shell multiwalled carbon nanotube@RuO2 lithium-ion battery electrodes through a RuO2 atomic layer deposition process.

ACS Nano 2015 Jan 22;9(1):464-73. Epub 2014 Dec 22.

Department of Materials Science and Engineering, University of Maryland , College Park, Maryland 20742, United States.

Pushing lithium-ion battery (LIB) technology forward to its fundamental scaling limits requires the ability to create designer heterostructured materials and architectures. Atomic layer deposition (ALD) has recently been applied to advanced nanostructured energy storage devices due to the wide range of available materials, angstrom thickness control, and extreme conformality over high aspect ratio nanostructures. A class of materials referred to as conversion electrodes has recently been proposed as high capacity electrodes. RuO2 is considered an ideal conversion material due to its high combined electronic and ionic conductivity and high gravimetric capacity, and as such is an excellent material to explore the behavior of conversion electrodes at nanoscale thicknesses. We report here a fully characterized atomic layer deposition process for RuO2, electrochemical cycling data for ALD RuO2, and the application of the RuO2 to a composite carbon nanotube electrode scaffold with nucleation-controlled RuO2 growth. A growth rate of 0.4 Å/cycle is found between ∼ 210-240 °C. In a planar configuration, the resulting RuO2 films show high first cycle electrochemical capacities of ∼ 1400 mAh/g, but the capacity rapidly degrades with charge/discharge cycling. We also fabricated core/shell MWCNT/RuO2 heterostructured 3D electrodes, which show a 50× increase in the areal capacity over their planar counterparts, with an areal lithium capacity of 1.6 mAh/cm(2).
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http://dx.doi.org/10.1021/nn505644qDOI Listing
January 2015

An all-in-one nanopore battery array.

Nat Nanotechnol 2014 Dec 10;9(12):1031-9. Epub 2014 Nov 10.

1] Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA [2] Institute for Systems Research, University of Maryland, College Park, Maryland 20742, USA.

A single nanopore structure that embeds all components of an electrochemical storage device could bring about the ultimate miniaturization in energy storage. Self-alignment of electrodes within each nanopore may enable closer and more controlled spacing between electrodes than in state-of-art batteries. Such an 'all-in-one' nanopore battery array would also present an alternative to interdigitated electrode structures that employ complex three-dimensional geometries with greater spatial heterogeneity. Here, we report a battery composed of an array of nanobatteries connected in parallel, each composed of an anode, a cathode and a liquid electrolyte confined within the nanopores of anodic aluminium oxide, as an all-in-one nanosize device. Each nanoelectrode includes an outer Ru nanotube current collector and an inner nanotube of V₂O₅ storage material, forming a symmetric full nanopore storage cell with anode and cathode separated by an electrolyte region. The V₂O₅ is prelithiated at one end to serve as the anode, with pristine V₂O₅ at the other end serving as the cathode, forming a battery that is asymmetrically cycled between 0.2 V and 1.8 V. The capacity retention of this full cell (relative to 1 C values) is 95% at 5 C and 46% at 150 C, with a 1,000-cycle life. From a fundamental point of view, our all-in-one nanopore battery array unveils an electrochemical regime in which ion insertion and surface charge mechanisms for energy storage become indistinguishable, and offers a testbed for studying ion transport limits in dense nanostructured electrode arrays.
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http://dx.doi.org/10.1038/nnano.2014.247DOI Listing
December 2014

Simple SERS substrates: powerful, portable, and full of potential.

Phys Chem Chem Phys 2014 Feb;16(6):2224-39

Fischell Department of Bioengineering, University of Maryland, College Park, MD, USA.

Surface enhanced Raman spectroscopy (SERS) is a powerful spectroscopic technique capable of detecting trace amounts of chemicals and identifying them based on their unique vibrational characteristics. While there are many complex methods for fabricating SERS substrates, there has been a recent shift towards the development of simple, low cost fabrication methods that can be performed in most labs or even in the field. The potential of SERS for widespread use will likely be realized only with development of cheaper, simpler methods. In this Perspective article we briefly review several of the more popular methods for SERS substrate fabrication, discuss the characteristics of simple SERS substrates, and examine several methods for producing simple SERS substrates. We highlight potential applications and future directions for simple SERS substrates, focusing on highly SERS active three-dimensional nanostructures fabricated by inkjet and screen printing and galvanic displacement for portable SERS analysis - an area that we believe has exciting potential for future research and commercialization.
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http://dx.doi.org/10.1039/c3cp53560fDOI Listing
February 2014

In situ transmission electron microscopy study of electrochemical lithiation and delithiation cycling of the conversion anode RuO2.

ACS Nano 2013 Jul 25;7(7):6354-60. Epub 2013 Jun 25.

Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA.

Conversion-type electrodes represent a broad class of materials with a new Li(+) reactivity concept. Of these materials, RuO2 can be considered a model material due to its metallic-like conductivity and its high theoretical capacity of 806 mAh/g. In this paper, we use in situ transmission electron microscopy to study the reaction between single-crystal RuO2 nanowires and Li(+). We show that a large volume expansion of 95% occurs after lithiation, 26% of which is irreversible after delithiation. Significant surface roughening and lithium embrittlement are also present. Furthermore, we show that the initial reaction from crystalline RuO2 to the fully lithiated mixed phase of Ru/Li2O is not fully reversible, passing through an intermediate phase of LixRuO2. In subsequent cycles, the phase transitions are between amorphous RuO2 in the delithiated state and a nanostructured network of Ru/Li2O in the fully lithiated phase.
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http://dx.doi.org/10.1021/nn402451sDOI Listing
July 2013

Natural cellulose fiber as substrate for supercapacitor.

ACS Nano 2013 Jul 21;7(7):6037-46. Epub 2013 Jun 21.

Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA.

Cellulose fibers with porous structure and electrolyte absorption properties are considered to be a good potential substrate for the deposition of energy material for energy storage devices. Unlike traditional substrates, such as gold or stainless steel, paper prepared from cellulose fibers in this study not only functions as a substrate with large surface area but also acts as an interior electrolyte reservoir, where electrolyte can be absorbed much in the cellulose fibers and is ready to diffuse into an energy storage material. We demonstrated the value of this internal electrolyte reservoir by comparing a series of hierarchical hybrid supercapacitor electrodes based on homemade cellulose paper or polyester textile integrated with carbon nanotubes (CNTs) by simple solution dip and electrodeposited with MnO2. Atomic layer deposition of Al2O3 onto the fiber surface was used to limit electrolyte absorption into the fibers for comparison. Configurations designed with different numbers of ion diffusion pathways were compared to show that cellulose fibers in paper can act as a good interior electrolyte reservoir and provide an effective pathway for ion transport facilitation. Further optimization using an additional CNT coating resulted in an electrode of paper/CNTs/MnO2/CNTs, which has dual ion diffusion and electron transfer pathways and demonstrated superior supercapacitive performance. This paper highlights the merits of the mesoporous cellulose fibers as substrates for supercapacitor electrodes, in which the water-swelling effect of the cellulose fibers can absorb electrolyte, and the mesoporous internal structure of the fibers can provide channels for ions to diffuse to the electrochemical energy storage materials.
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http://dx.doi.org/10.1021/nn401818tDOI Listing
July 2013

Optically clear alginate hydrogels for spatially controlled cell entrapment and culture at microfluidic electrode surfaces.

Lab Chip 2013 May 5;13(10):1854-8. Epub 2013 Apr 5.

Fischell Department of Bioengineering, University of Maryland, College Park, MD, USA.

We describe an innovation in the immobilization, culture, and imaging of cells in calcium alginate within microfluidic devices. This technique allows unprecedented optical access to the entirety of the calcium alginate hydrogel, enabling observation of growth and behavior in a chemical and mechanical environment favored by many kinds of cells.
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http://dx.doi.org/10.1039/c3lc50079aDOI Listing
May 2013

A beaded-string silicon anode.

ACS Nano 2013 Mar 20;7(3):2717-24. Epub 2013 Feb 20.

Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States.

Interfacial instability is a fundamental issue in heterostructures ranging from biomaterials to joint replacement and electronic packaging. This challenge is particularly intriguing for lithium ion battery anodes comprising silicon as the ion storage material, where ultrahigh capacity is accompanied by vast mechanical stress that threatens delamination of silicon from the current collectors at the other side of the interface. Here, we describe Si-beaded carbon nanotube (CNT) strings whose interface is controlled by chemical functionalization, producing separated amorphous Si beads threaded along mechanically robust and electrically conductive CNT. In situ transmission electron microscopy combined with atomic and continuum modeling reveal that the chemically tailored Si-C interface plays important roles in constraining the Si beads, such that they exhibit a symmetric "radial breathing" around the CNT string, remaining crack-free and electrically connected throughout lithiation-delithiation cycling. These findings provide fundamental insights in controlling nanostructured interfaces to effectively respond to demanding environments such as lithium batteries.
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http://dx.doi.org/10.1021/nn4001512DOI Listing
March 2013

Autonomous bacterial localization and gene expression based on nearby cell receptor density.

Mol Syst Biol 2013 ;9:636

Fischell Department of Bioengineering, University of Maryland, College Park, MD, USA.

Escherichia coli were genetically modified to enable programmed motility, sensing, and actuation based on the density of features on nearby surfaces. Then, based on calculated feature density, these cells expressed marker proteins to indicate phenotypic response. Specifically, site-specific synthesis of bacterial quorum sensing autoinducer-2 (AI-2) is used to initiate and recruit motile cells. In our model system, we rewired E. coli's AI-2 signaling pathway to direct bacteria to a squamous cancer cell line of head and neck (SCCHN), where they initiate synthesis of a reporter (drug surrogate) based on a threshold density of epidermal growth factor receptor (EGFR). This represents a new type of controller for targeted drug delivery as actuation (synthesis and delivery) depends on a receptor density marking the diseased cell. The ability to survey local surfaces and initiate gene expression based on feature density represents a new area-based switch in synthetic biology that will find use beyond the proposed cancer model here.
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http://dx.doi.org/10.1038/msb.2012.71DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3564257PMC
September 2013

MWCNT/V2O5 core/shell sponge for high areal capacity and power density Li-ion cathodes.

ACS Nano 2012 Sep 15;6(9):7948-55. Epub 2012 Aug 15.

Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, United States.

A multiwall carbon nanotube (MWCNT) sponge network, coated by ALD V(2)O(5), presents the key characteristics needed to serve as a high-performance cathode in Li-ion batteries, exploiting (1) the highly electron-conductive nature of MWCNT, (2) unprecedented uniformity of ALD thin film coatings, and (3) high surface area and porosity of the MWCNT sponge material for ion transport. The core/shell MWCNT/V(2)O(5) sponge delivers a stable high areal capacity of 816 μAh/cm(2) for 2 Li/V(2)O(5) (voltage range 4.0-2.1 V) at 1C rate (1.1 mA/cm(2)), 450 times that of a planar V(2)O(5) thin film cathode. At much higher current (50×), the areal capacity of 155 μAh/cm(2) provides a high power density of 21.7 mW/cm(2). The compressed sponge nanoarchitecture thus demonstrates exceptional robustness and energy-power characteristics for thin film cathode structures for electrochemical energy storage.
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http://dx.doi.org/10.1021/nn302417xDOI Listing
September 2012

Biofabrication of stratified biofilm mimics for observation and control of bacterial signaling.

Biomaterials 2012 Jul 14;33(20):5136-43. Epub 2012 Apr 14.

Institute for Bioscience and Biotechnology Research, University of Maryland, College Park, MD 20742, USA.

Signaling between cells guides biological phenotype. Communications between individual cells, clusters of cells and populations exist in complex networks that, in sum, guide behavior. There are few experimental approaches that enable high content interrogation of individual and multicellular behaviors at length and time scales commensurate with the signal molecules and cells themselves. Here we present "biofabrication" in microfluidics as one approach that enables in-situ organization of living cells in microenvironments with spatiotemporal control and programmability. We construct bacterial biofilm mimics that offer detailed understanding and subsequent control of population-based quorum sensing (QS) behaviors in a manner decoupled from cell number. Our approach reveals signaling patterns among bacterial cells within a single biofilm as well as behaviors that are coordinated between two communicating biofilms. We envision versatile use of this biofabrication strategy for cell-cell interaction studies and small molecule drug discovery.
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http://dx.doi.org/10.1016/j.biomaterials.2012.03.037DOI Listing
July 2012

Electrodeposition of a biopolymeric hydrogel: potential for one-step protein electroaddressing.

Biomacromolecules 2012 Apr 26;13(4):1181-9. Epub 2012 Mar 26.

Institute for Bioscience and Biotechnology Research, University of Maryland, College Park, Maryland 20742, United States.

The electrodeposition of hydrogels provides a programmable means to assemble soft matter for various technological applications. We report an anodic method to deposit hydrogel films of the aminopolysaccharide chitosan. Evidence suggests the deposition mechanism involves the electrolysis of chloride to generate reactive chlorine species (e.g., HOCl) that partially oxidize chitosan to generate aldehydes that can couple covalently with amines (presumably through Schiff base linkages). Chitosan's anodic deposition is controllable spatially and temporally. Consistent with a covalent cross-linking mechanism, the deposited chitosan undergoes repeated swelling/deswelling in response to pH changes. Consistent with a covalent conjugation mechanism, proteins could be codeposited and retained within the chitosan film even after detergent washing. As a proof-of-concept, we electroaddressed glucose oxidase to a side-wall electrode of a microfabricated fluidic channel and demonstrated this enzyme could perform electrochemical biosensing functions. Thus, anodic chitosan deposition provides a reagentless, single-step method to electroaddress a stimuli-responsive and biofunctionalized hydrogel film.
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http://dx.doi.org/10.1021/bm3001155DOI Listing
April 2012

Nanoengineering strategies for metal-insulator-metal electrostatic nanocapacitors.

ACS Nano 2012 Apr 14;6(4):3528-36. Epub 2012 Mar 14.

Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, United States.

Nanostructures can improve the performance of electrical energy storage devices. Recently, metal-insulator-metal (MIM) electrostatic capacitors fabricated in a three-dimensional cylindrical nanotemplate of anodized aluminum oxide (AAO) porous film have shown profound increase in device capacitance (100× or more) over planar structures. However, inherent asperities at the top of the nanostructure template cause locally high field strengths and lead to low breakdown voltage. This severely limits the usable voltage, the associated energy density (1/2 CV(2)), and thus the operational charge-discharge window of the device. We describe an electrochemical technique, complementary to the self-assembled template pore formation process in the AAO film, that provides nanoengineered topographies with significantly reduced local electric field concentrations, enabling breakdown fields up to 2.5× higher (to >10 MV/cm) while reducing leakage current densities by 1 order of magnitude (to ∼10(-10) A/cm(2)). In addition, we consider and optimize the AAO template and nanopore dimensions, increasing the capacitance per planar unit area by another 20%. As a result, the MIM nanocapacitor devices achieve an energy density of ∼1.5 Wh/kg--the highest reported.
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http://dx.doi.org/10.1021/nn300553rDOI Listing
April 2012

Direct SERS detection of contaminants in a complex mixture: rapid, single step screening for melamine in liquid infant formula.

Analyst 2012 Feb 10;137(4):826-8. Epub 2012 Jan 10.

Fischell Department of Bioengineering, University of Maryland, College Park, MD, USA.

Melamine can be detected in infant formula without the need for additional sample preparation or purification using a simple galvanic displacement reaction to fabricate portable silver SERS substrates. The reaction is rapid, inexpensive, and robust enough to perform well on highly heterogeneous common metal objects such as tape and coins.
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http://dx.doi.org/10.1039/c2an15846aDOI Listing
February 2012