Highlights


Precision + Structure: Four Years of Nanostructures for Electrical Energy Storage

Precision + Structure: Four Years of Nanostructures for Electrical Energy Storage

Precision + Structure: Four Years of Nanostructures for Electrical Energy Storage, an intriguing glimpse into NEES' research directions and advances since its funding in 2009.

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Pioneering Ionic Current Probe of MnO2 Mesorods in Single Nanopore

Pioneering Ionic Current Probe of MnO2 Mesorods in Single Nanopore

Siwy and Lee Research Groups - Thrust A

Scientific Achievement

For the first time, researchers have applied ionic current to directly probe both structural and electrochemical characterizations of nanoporous manganese oxide mesorods deposited in a single polymer pore. The present results showed the existence of nanovoids with effective diameters <5nm, which carried negative surface charge with metal cation selectivity.

Significance and Impact

Understanding ion transport mechanisms in confined space of metal oxide materials can have a revolutionary impact in electrochemical energy storage technology, as applied to lithium ion batteries and supercapacitors. The reported novel method using ionic current provides a valuable probe for charge polarity and species-selective transport in electrode nanomaterials.

Research Details

  • Resistance and current measurements supported a meshlike porous character for the deposited MnO2.
  • Current saturation experiments at low electrolyte concentration showed the existence of nanovoids with effective diameters less than 5nm.
  • Reversal potential measurements under salt concentration gradient indicated negatively charged surface area and selectivity for metal cations such as Li+ but not protons.

Summary

Research groups at Nanostructures of Electrical Energy Storage (NEES) EFRC applied ionic current as a novel method to probe the nanoporous structures and physical properties of MnO2 deposited as mesorods inside a single pore in a polymer film of polyethylene terephthalate (PET). Similar approach had been applied previously to polymer nanopores and biological channels, but not in application to metal oxide materials such as MnO2. Although data on characterization of manganese oxide in bulk are available, little information is forth coming on its transport mechanism under confined structural configurations, as in the case of the present study. Resistance and current measurements supported a meshlike porous character for the deposited MnO2. Additional current saturation experiment at low electrolyte concentration confirmed that the effective diameters of the voids are in nanometer range. Under cross-membrane salt concentration gradient, reversal potential measurements indicated that the nanovoids are negatively charged and are selective for metal cations such as Li+, but not protons. Observed nonlinear current-voltage curves suggested an asymmetrical nanopore structures with directional selectivity. These results laid the foundation for future investigation of the MnO2 nanotructures during charging/discharge cycles.

References

T. Gamble, E. Gillette, S.B. Lee and Z.S. Siwy, "Probing Porous Structure of Single Manganese Oxide Mesorods with Ionic Current" The Journal of Physical Chemistry C (2013), 117 (47), pp 24836-24842. http://pubs.acs.org/doi/pdf/10.1021/jp408107z

Nanoglue for Hybrid Nanostructures in Na Ion Anodes

Nanoglue for Hybrid Nanostructures in Na Ion Anodes

Liangbing Hu Group (UMD)

Scientific Achievement

In situ TEM studies show that atomic layer deposition (ALD)-Al2O3 coating forms an artificial solid electrolyte interface (SEI) layer, which robustly anchors Sn nanoparticles (SnNPs) to carbon nanofibers (CNF) and undergoes volume changes synergistically with the SnNP core during sodiation cycling.

Significance and Impact

Highly conformal coatings offer mechanisms for robust binding of nanoparticle active storage material to current-collecting substrates, demonstrated here for ALD-Al2O3 to bind Sn nanoparticles to carbon fibers.

Research Details

  • Na-Al-O layer formed irreversibly from a 3-5nm SnO2 sub layer & ALD-Al2O3 coating in initial surface sodiation.
  • Coin-cell battery using liquid electrolyte showed stabilized specific capacity of 650 (vs 110) mAh/g after 40 cycles with (vs without) ALD-Al2O3 coating.
  • Finite element simulations: Na-Al-O layer (thickness-dep) delays debonding initiation & allows capacity retention beyond interfacial delamination at 67% volume expansion.

Summary

Combined with tin's high theoretical specific capacity, Na ion batteries (NIBs) have increasingly become an attractive candidate for grid-scale energy storage due to its low cost and abundance. But as Si is for Li ion batteries, Sn experiences huge volume expansion (420%) upon sodiation, a grand challenge for both structural and cycle stability during charging/discharging. Researchers at Nanostructures for Electrical Energy Storage (NEES) EFRC have conducted a real time mechanistic characterization of atomic-layer-deposition Al2O3 (ADL-Al2O3) coatings on the hybrid nanostructure anode (SnNPS@CNF) during sodiation/desodiation.

In situ TEM electrochemical tests demonstrated the irreversible formation of Na-Al-O layer as an artificial solid electrolyte interface (SEI), acting as an ion conductive nanoglue that deforms coherently in synch with volume expansion of the encased nanoparticle core after repeated cycling. In coin-cell battery made from ALD-Al2O3 anode materials, a charge capacity of 650 mAh/g was maintained without capacity fade for 40 cycles, compared to 110 mAh/g of the bare SnNPs@CNF. Finite Element Method simulations supported the observation that Na-Al-O layer mechanically protects the contact between SnNPs and CNF during volume expansion, even after initiation of debonding.

Reference

Xiaogang Han, Yang Liu, Zheng Jia, Yu-Chen Chen, Jiayu Wan, Nicholas Weadock, Karen J. Gaskell, Teng Li and Liangbing Hu, Nano Letters (2014) 14, 139-147. DOI: 10.1021/nl4035626

Si Nanowire Anodes with Long Cycle Lives

Si Nanowire Anodes with Long Cycle Lives

S. Tom Picraux Group (LANL)

Scientific Achievement

Nanoporous AAO template has been used to guide VLS growth of Si nanowires and prevent Si island formation by reaction with underlying metal collector, yielding excellent cycle life (> 1100) and specific capacity (1000 mAh/g) for high density SiNW arrays.

Significance and Impact

Achieving viable nanostructured electrode arrays requires careful attention to all relevant reaction pathways and 3-D design.

Research Details

  • High density SiNW forests were deposited on stainless steel using bottom-up vapor-liquid-solid growth by chemical vapor deposition through AAO templates containing high density of sub-100nm nanopores.
  • Specific capacity measurements & SEM images show that elimination of milli- & microscale Si underlayer islands allows stable SiNW-current collector contacts during cycling, retaining Si's high charge capacity.

Summary

Interests in silicon's high theoretical capacity (4200 mA-h/g) as an anode in lithium-ion batteries and the accompanied challenge of its huge volume expansion (~300%) during charge/discharge cycling, have driven research effort into high density one-dimensional Si nanomaterials. Although the use of nanoscale Si materials allows lateral relaxation and reduces mechanical stress of the Si electrodes, cycle stability >50 under high charging rates has yet to be realized, a crucial step toward industrial battery application. Scientists at Nanostructures for Electrical Energy Storage (NEES) EFRC have successfully improved cycle stability to >1100 while retaining 1000 mA-h/g specific capacities under high cycle rates (10C) for Si nanowires (SiNW) as Li-ion anode.

They discovered the existence of underlayer Si islands at the interface of the SiNW and the current collector, as an auxiliary deposits during chemical vapor deposition (CVD) synthesis process. SEM images showed cracks in these islands that prevented retention of specific capacity beyond 200 cycles, due to disruption of electrical contact between SiNW and current collector. Modifications in the bottom-up, vapor-liquid-solid (VLS) growth process employing anodized aluminum oxide (Al2O3) templates containing a high density of sub-100 nm nanopores eliminated the underlayer Si island formation.

Reference

Jeong-Hyun Cho and S. Tom Picraux, Nano Letters (2013) 13, 5740-5747. http://dx.doi.org/10.1021/nl4036498.

Hoop-Strong Nanotubes for Battery Electrodes

Hoop-Strong Nanotubes for Battery Electrodes

Scientific Achievement

Chemically inert Ni coating outside Si nanotubes (NTs) constrains Si to expand inward upon lithiation, enhancing structural stability and charge/discharge cyclability.

Significance and Impact

Functional coatings can prevent structural instability while enhancing electron transport to exploit Si as high capacity nanostructured anode.

Research Details

  • In-situ TEM shows outward expansion of Si NTs if uncoated or with native oxide, leading to structural instability of Si and solid-electrolyte-interphase (SEI) during repeated cycling.
  • Ni outer coating of 16 nm prevents outer surface expansion, forcing lithiation-induced expansion inward.
  • Ni-coated SiNTs show dramatically better capacity retention (85% at 100 cycles)

Reference

K. Karki, Y. Zhu, Y. Liu, C.-F. Sun, L. Hu, Y. Wang, C. Wang, and J. Cumings. "Hoop-Strong Nanotubes for Battery Electrodes." ACS Nano (2013) DOI: 10.1021/nn403895h

Energy Textile from Weavable High-Capacity Electrodes

Energy Textile from Weavable High-Capacity Electrodes

YuHuang Wang Group (UMD)

Scientific Achievement

A highly scalable process was developed to produce a mechanically robust and electrically conductive Si-carbon nanotube (CNT) composite yarn, with discharge capacity five times that of graphite anodes.

Significance and Impact

NEES researchers have taken a further step to translate their scientific advance in hybrid Si@CNT nanostructures into fabric-like form factors amenable to evaluation as prototype battery technology.

Research Details

  • Vertically aligned CNT arrays (50 nm in diameter,750 ?m in length) were spun into a porous yarn, layered with a-Si via low pressure CVD at Si:CNT mass ratio of 0.63.
  • Si-CNT composite yarn showed a discharge capacity of 2200 mA h/g based on the Si mass, in the first 10 cycles with a cutoff of 0.1-1.0 V.
  • Mechanically durable, flexible, scalable, with high electrical conductivity
  • Fabrication control on porosity (twisting force) & Si mass

Summary

Adopting from textile technology, scientist at NEES EFRC designed and synthesized a Si-carbon nanotube (CNT) composite yarn that demonstrates a multitude of materials qualities desirable for electrical energy storage. It is mechanically strong, flexible, and highly scalable and possesses high electrical conductivity. A Li-storage capacity as high as 2200 mA h/g based on the Si mass in the first 10 cycles with a cutoff of 0.1-1.0 V was achieved, five times higher than that of the typical graphite electrodes. This high capacitance also exceeds previous reports from fabrication of supercapacitor yarns by electrodeposition using MnOx as the active materials.

Vertically aligned CTN arrays (each CNT approximately 750 ?m in length and 50 nm in diameter) grown by chemical vapor deposition (CVD) were spun into a yarn, followed by low pressure CVD of amorphous Si at a Si:CNT mass ratio of 0.63. The loading of active material Si per area for this yarn is ?2.5 mg/ and can be controlled by the growth time for Si. The porosity of the yarns can be controlled by cm2 adjusting the twisting force during the spinning process. The resulting yarn is highly porous, with ability to accommodate the volume expansion of Si upon electrochemical charging.

Reference

Chuan-Fu Sun, Hongli Zhu, Edward B. Baker III, Morihiro Okada, Jiayu Wan, Adrian Ghemes, Yoku Inoue, Liangbing Hu, YuHuang Wang Nano Energy (2013) 2, 987. http://dx.doi.org/10.1016/j.nanoen.2013.03.020

Real Time Observation of Breathable Silicon Beads on a Robust Carbon Nanotube String

Real Time Observation of Breathable Silicon Beads on a Robust Carbon Nanotube String

YuHuang Wang's research group - Thrust B

Scientific Achievement

Researchers have built upon the heterogeneous carbon nanotube (CNT) as the current collector and Si as the ion storage material of ultrahigh capacity through selective chemical functionalization of the Si-CNT interface layer. A stable silicon nanobeads on a CNT structure was formed that radially swells and shrinks without cracking while maintaining electrical connectivity during lithiation/delithiation cycling. Chemical functional groups on the Si/C interface localize, separate, and anchor the beads, making Si's high energy storage capacity attainable.

Significance and Impact

Interfacial structural instability is a long-standing challenge in lithium ion battery anodes where silicon expands ~300% in volume during lithiation/delithiatin cycling. Studies here demonstrated that chemically controlled Si-Carbon nanotube interface can accommodate the huge volume change during lithiation/delithiation cycling, with stable structural integrity (no cracking) and intact electrical conductivity. This is a scientific breakthrough to harness silicon's potential for ultrahigh capacity as an anode material.

Summary

The Nanostructures for Electrical Energy Storage (NEES) EFRC investigates how the structure of materials at the nanoscale affects electrical energy storage. By growing silicon into the geometry of anchored beads on a carbon nanotube string, researchers created a nanostructure that can withstand significant radial expansion during lithiation/delithiation cycles without cracking.

Earlier NEES work reported that silicon nanoparticles under the critical diameter of 150 nm did not fracture when lithiated (DOI: 10.1021/nn204476h). Building on work that confined the propagation of functional groups on carbon nanotubes (DOI: 10.1038/ncomms1384), researchers grew silicon beads 200 nm in diameter that were anchored on carboxylic acid functional groups attached to the CNT. As observed by In situ TEM, cracks formed during charging and discharging in the tubular core-shell nanostructures but not in the functionalized beaded-string nanostructures. DFT and FEM computations revealed that in both cases tensile stresses developed in the unlithiated silicon due to the large volume expansion in the lithiated silicon phase, but strong covalent bond between the carboxylic acid function group and silicon prevented the silicon beads from cracking. These findings provide important new insights in the synthesis of high performance Si electrodes, laying a foundation for the next generation lithium ion batteries.

Research Details

  • Each silicon bead of 200 nm in diameter was anchored on carboxylic acid functional groups attached to the CNT surface.
  • During lithiation, the lithiated-silicon phase grows starting both from the outer bead surface and from the CNT-silicon interface.
  • In situ TEM observation showed that cracks formed in the tubular core-shell nanostructures but not in the functionalized beaded-string nanostructures during charging and discharging cycling.
  • DFT and FEM computations revealed that in both cases tensile stresses developed in the unlithiated silicon due to the large volume expansion in the lithiated silicon phase, but strong covalent bond between the carboxylic acid function group and silicon prevented the silicon beads from cracking.

References

Chuan-Fu Sun, Khim Karki, Zheng Jia, Hongwei Liao, Yin Zhang, Teng Li, Yue Qi, John Cumings, Gary W. Rubloff, and YuHuang Wang, "A Beaded-String Silicon Anode" ACS Nano (2013), 7, pp 2717-24. http://dx.doi.org/10.1021/nn4001512

Shunliu Deng, Yin Zhang, Alexandra H. Brozena, Maricris Lodriguito Mayes, Parag Banerjee, Wen-An Chiou, Gary W. Rubloff, George C. Schatz & YuHuang Wang, "Confined Propagation of Covalent Chemical reactions on Single-Walled Carbon Nanotubes" Nat Commun (2011) 2, p382. http//dx.doi.org/10.1038/ncomms1384

Lithium-Assisted Electrochemical Welding in Silicon Nanowire Battery Electrodes

Lithium-Assisted Electrochemical Welding in Silicon Nanowire Battery Electrodes

Thrust B

Accomplishment

  • Inside a TEM, the researchers crossed two silicon nanowires connected to a common substrate and touched the free end of one wire to lithium metal with a LiO2 oxide coating. With an applied bias to the substrate, both nanowires lithiated and fused, creating a lithium-ion-conducting region between them.
  • Applying force to the cantilevered nanowires with the probe tip, the researchers estimated the shear strength of the node. Their analytical models gave the minimum shear strength to be 200 MPa, which compares to the strength of stainless steel (~205 MPa) and ceramic silicon carbide (~200 MPa), and a finite-element model found 308 MPa.
  • The researchers proposed a kinetic driving force for the fusion. During lithiation, lithium ions bind with the surface silicon atoms on both wires simultaneously, creating metastable Li-Si bonds. During delithiation, the Si-Li-Si bonds break, and neighboring surface Si atoms bond to each other and fuse the nanowires together.

Significance

  • The formation of fused regions between silicon nanowires is a critical first step toward self-healing networks of silicon and energy storage materials that may otherwise crack and lose contact with a current collector during charging and discharging.
  • The room temperature method for creating the nodes is a facile method for controlling the number and location of fused regions between wires. Tailoring architectures of nanowire networks could provide a platform for further probing energy storage properties of nanostructures.

Reference

K. Karki et al., Lithium-Assisted Electrochemical Welding in Silicon Nanowire Battery Electrodes. Nano Letters 12, 1392 (2012/03/14, 2012). (coauthors: Karki, Khim; Epstein, Eric; Cho, Jeong-Hyun; Jia, Zheng; Li, Teng; Picraux, S. Tom; Wang, Chunsheng; Cumings, John) DOI: 10.1021/nl204063u

MnO2-Gold Nanowires with Ultra-high Charge Storage

MnO2-Gold Nanowires with Ultra-high Charge Storage

R Penner Group (UCI) - Thrust A

Scientific Achievement

MnO2 nanowire electrodes with gold cores show ultra-high charge storage for 1000 charging and discharging cycles. Controlling the structure down to 2 nm scale increased the specific capacity, and employing a dry electrolyte greatly increased cycle stability. The nanowires can precisely measure MnO2 electrochemical properties without ohmic drops, which would occur in real battery electrodes. The mesoporous-MnO2 nanowires synthesized here showed a hybrid ultra-high specific capacity of 1020 F/g at 5 mV/s.

Significance and Impact

Controlling structure at the nanoscale unlocks nearly the full theoretical specific capacity from two of three storage mechanisms in MnO2. The present design of core/shell nanowires allows researchers to partially decouple the mechanisms that contribute to the observed ultra-high capacity, making it feasible to further increase the capacity, rate, and cycle stability in MnO2 and other charge storage materials.

Research Details

  • The LPNE (lithographically patterned nanowire electrodeposition) technique deposited gold current collector nanowires 40 nm tall and 150-250 nm wide with MnO2 shells 50-250 nm thick. The porous nanowires were 0.1 - 1 cm long and were made of 2 nm-thick fibrils.
  • Electrochemical measurements were taken with 1.0 M LiClO4 in dry acetonitrile. The dry electrolyte prevents Mn2+ from dissolving out of the material and degrading it.
  • Because fibrils are so small, all Mn ions are close to surfaces and therefore can contribute to multiple charge storage mechanisms.

Summery

The Nanostructures for Electrical Energy Storage (NEES) EFRC investigates precision nanoparticles, nanowires, nanotubes, and nanometer-thick films to understand how the structure of materials affects charge storage mechanisms. Most reported nano-MnO2 electrodes show specific capacity values of 200-600 F/g, with a few reports up to 1380 F/g. The mesoporous-MnO2 nanowires synthesized here show hybrid ultra-high specific capacity of 1020 F/g at 5 mV/s. Cycle stability of this capacity up to 1000 cycles is achieved using dry acetonitrile electrolytes to eliminate dissolution of MnO2 during cycling.

The charge storage in MnO2 electrodes occurred via two faradaic and one nonfaradaic mechanisms. Electron transfers between ions in the electrolyte and Mn ions on the surface of MnO2 occur in faradaic pseudocapacitance mechanism. For the faradaic insertion mechanism, the electrolyte ions diffuse into the bulk MnO2 materials for the oxidation-reduction reactions to occur, which is the dominant charge storage in batteries. The one nonfaradaic charge storage in MnO2 occurs from double-layer capacitance at interface, which is the dominant charge storage in supercapacitors.

Using variable dependency of voltammetric current on potential scan rates, researchers were able to deconvolute insertion vs. noninsertion capacitances. They found that the high specific capacity in thin-shell MnO2 nanowires is largely due to changes in the faradaic insertion capacity, as it is rate-limited by cation diffusion in MnO2.

Reference

W. Yan, J. Y. Kim, W. Xing, K. C. Donavan, T. Ayvazian, R. M. Penner "Lithographically Patterned Gold/Manganese Dioxide Core/Shell Nanowires for High Capacity, High Rate, and High Cyclability Hybrid Electrical Energy Storage" Chemistry of Materials, 2012, 24, 2382-2390. DOI: 10.1021/cm3011474

First-Principles Modeling of the Initial Stages of Organic Solvent Decomposition on LixMn2O4(100) Surfaces

First-Principles Modeling of the Initial Stages of Organic Solvent Decomposition on LixMn2O4(100) Surfaces

Thrust E

Accomplishment

Quantum mechanical modeling of ethylene carbonate (EC) on the surface of Li0.6Mn2O4 (manganese spinel positive electrode) reveals an unexpected mechanism for EC breakdown. EC is a component of standard lithium-ion battery electrolytes. The local interaction between EC and the surface ions, not electron transfer (oxidation), initiates the EC decomposition, which eventually also weakens the electrode surface structure.

Significance

No previous atomistic modeling study has examined an organic solvent molecule on a lithium ion battery positive electrode oxide surface. Finding that the reactive manganese spinel surface is enough to destabilize EC contributes to understanding how electrolytes and positive electrodes degrade after many battery cycles.

Research Details

  • The breakdown of EC on negative electrode surfaces has been well studied. There the breakdown products lead to the considerable growth of a solid-electrolyte interphase, a composite that both inhibits and protects battery operation. On positive electrode surfaces, previous computational studies have modeled electrodes under ultra high vacuum conditions or water on oxide surfaces.
  • Since the intrinsic potential of EC is higher than manganese spinel, electrons are not expected to transfer between EC and the oxide, and if surface effects were not considered, no EC degradation therefore would be expected to occur despite their proximity to each other.
  • The molecular dynamics calculations provided a five-stage process for the decomposition of EC due to surface interactions. Additional ultrahigh vacuum condition calculations quantified the energy profile of the system across the stages and quantified the activation energy for reaction steps.

Reference

Kevin Leung, "First-Principles Modeling of the Initial Stages of Organic Solvent Decomposition on LixMn2O4(100) Surfaces." J. Phys. Chem. C, 2012, 116 (18), pp 9852-9861 DOI: 10.1021/jp212415x

Highly flexible pseudocapacitor based on freestanding heterogeneous MnO2/conductive polymer nanowire arrays

Highly flexible pseudocapacitor based on freestanding heterogeneous MnO2/conductive polymer nanowire arrays

Thrust A

Scientific Achievement

Duay, et. al. synthesized asymmetric pseudocapacitors made of PEDOT nanowire anodes opposite coaxial MnO2/PEDOT nanowire cathodes. Outperforming symmetric pseudocapacitors of MnO2/PEDOT nanowires alone, the asymmetric cells had a larger voltage window leading to higher energy density, had high power density and cycle life, and maintained 86 % of the energy density in a highly flexed state.

Significance & Impact

Flexible, high capacity, high power energy storage is critical for widespread use of wearable device fabrics and flexible biomedical devices. By discerning the limitations of coaxial MnO2/PEDOT nanowires as anodes yet capitalizing on their properties as cathodes, the researchers improved the supercapacitor performance with a new architecture, providing for higher performance than existing supercapacitors reported in literature.

Research Details

  • MnO2/PEDOT coaxial nanowires show superior performance as electrodes in half-cell measurements. PEDOT acts as a flexible mechanical scaffold with high ion permeability and high electrical conductivity. MnO2 provides high energy density. This study examined their performance in full-cell pseudocapacitor configuration.
  • Experiments on the symmetric full cells showed that coaxial MnO2/PEDOT nanowires were limiting as anode materials because the wide voltage window of PEDOT overlapped the irreversibility window of MnO2. As the coaxial nanowire anode cycled, electrochemically inactive Mn2+ started to form, decreasing the amount of energy storage material available.
  • With reconfigured electrodes, the asymmetric pseudocapacitors of PEDOT anodes and MnO2/PEDOT cathodes reached 0.26 F total capacitance and a maximum voltage at 1.7 V. The energy density was 9.8 Wh/kg at a power density of 850 W/kg.

Reference

Jonathon Duay, Eleanor Gillette, Ran Liu, and Sang Bok Lee
Phys. Chem. Chem. Phys., 2012, 14, 3329-3337
DOI: 10.1039/C2CP00019A

Mapping of near field light and fabrication of complex nanopatterns by diffraction lithography

Mapping of near field light and fabrication of complex nanopatterns by diffraction lithography

Mark Reed Group (Yale) - Thrust B

Accomplishment

  • In a lithography experiment, the researchers quantified to very high accuracy the intensity of light diffracting from a mask onto photoresist by using a simple, single-step process. The diffraction followed classical Fresnel diffraction theory.
  • Taking advantage of the Poisson spot from the diffraction, they synthesized nanostructures with subwavelength features using UV light (? = 405 nm).
    • Starting with a photomask with opaque, circular discs, they synthesized a regular array of uniform single-crystal silicon nanotubes (~500 nm diameter, ~10 nm wall thickness, ~2 ?m tall). See Figure (a). The wall thickness of the silicon tubes is <~100 nm, less than ~1/4 of the used wavelength, which conventional optical lithographies can hardly achieve.
    • With masks containing opaque triangles and squares, they finely tuned the diffraction patterns to create nanostructures of photoresist with multifold symmetries. See Figures (b) and (c).

Significance

  • The diffraction technique and the ability to transfer patterns onto substrates open the opportunity for researchers to synthesize uniform nanostructures on a large scale with novel geometries. The method can fabricate sub-wavelength features on a large-scale. By tuning geometries, researchers may study the effect of structure on lithium-ion charge storage.
  • This sub-wavelength feature fabrication is simple synthesis process; it does not require any extra fabrication steps or extra experimental apparatus over conventional lithographies.
  • This process is less expensive than other non-optical (e.g. e-beam lithography) or alternative optical (e.g. interference) lithographies that are capable of sub-wavelength feature fabrication but are generally very costly and require a series of fabrication process and experimental apparatus.

Reference

Y. Jung, A. Vacic, Y. Sun, E. Hadjimichael, M. A. Reed, Mapping of near field light and fabrication of complex nanopatterns by diffraction lithography. Nanotechnology 23, 045301 (2012).
DOI: 10.1088/0957-4484/23/4/045301

Controlled Growth of Functional Groups Preserves Carbon Nanotube Properties

Controlled Growth of Functional Groups Preserves Carbon Nanotube Properties

Y.H. Yang (UMD) - Thrust D

Accomplishment

A new electrokinetic phenomenon - electroosmotic flow rectification (EOF) - has been demonstrated.
  • Developed a process for the controlled growth of functional groups on single-walled carbon nanotubes (SWNTs).
  • At the step edges of implanted sp3 defects, functional groups covalently bond in sequential steps via a Billups-Birch alkylcarboxylation reaction and extend around the tube into a band. Continuing the reaction propagates the functionalized regions of -(CH2)nCOOH to controlled length along the tube.
  • Functional regions induce water solubility while intact regions maintain the SWNTs remarkable optical and electronic properties.

Significance

  • Covalent functionalization for the first time is separated from defect nucleation on a graphene lattice. This mechanism affords control of carbon surface chemistry much like the separation of crystal growth from seed nucleation.
  • Covalent modification is required for many applications of CNTs, but adding the necessary functional groups usually destroys the electronic and optical properties that make CNTs an attractive material. By localizing the functional groups in bands, the properties are largely preserved.
  • This discovery affords new control in making use of the excellent electrical conductivity of CNTs in lithium-ion battery studies.

Collaborators

S. Deng, Y. Zhang, A. H. Brozena, M. L. Mayes, P. Banerjee, W. A. Chiou, G. W. Rubloff, G. C. Schatz, Y. H. Wang

Reference

Deng, S.; Zhang, Y.; Brozena, A. H.; Mayes, M. L.; Banerjee, P.; Chiou, W. A.; Rubloff, G. W.; Schatz, G.C.; Wang, Y. H.*, Nature Communications 2:382 (2011) | DOI: 10.1038/ncomms1384
Nature Website Article
Maryland NanoCenter News Story

Real-time Observation of Charging a Single SnO2 Nanowire Anode with Lithium

Real-time Observation of Charging a Single SnO2 Nanowire Anode with Lithium

Jianyu Huang, John P. Sullivan (Sandia) - Thrust D

Accomplishment

  • Creation of the first nano battery inside a transmission electron microscope (TEM) - consisting of a single SnO2 nanowire anode, an ionic liquid electrolyte (ILE), and bulk LiCoO2 cathode - and the in-situ observation of the lithiation of the SnO2 nanowire during electrochemical charging.
  • The low vapor pressure of the ILE allowed direct observation of the process at the nanoscale in the vacuum environment of a TEM.
    • The SnO2 nanowire was in contact with an ILE drop that contained Li salt and that touched the LiCoO2 cathode.
    • Real-time TEM observations show the reaction front moving through the nanowire.
  • Li moves primarily through bulk diffusion into SnO2, reacting to form Li2O and initiating mechanical changes observed as nanowire bending and distortion.

Significance

  • These are the first definitive experiments to directly observe an electrochemically-induced reaction in Li-ion battery materials in real time with atomic-scale resolution inside a TEM.
  • Such real-time observations at the nanoscale promise a new level of understanding for the fundamental mechanisms of Li-ion battery reactions, e.g. the relative roles of bulk diffusion versus surface Li diffusion.
  • The approach is general and may be applied to most any Li-ion battery material of suitable thin cross-section or even to other electrochemical phenomena, such as electrodeposition.

Collaborators

Jianyu Huang, John P. Sullivan (Sandia)
Chongmin Wang (Pacific Northwest Lab)
Scott Mao (Univ. Pittsburg)
Ju Li (Univ. Pennsylvania)

Supporting material

"In Situ Observation of the Electrochemical Lithiation of a Single SnO2 Nanowire Electrode" Jian Yu Huang, Li Zhong, Chong Min Wang, John P. Sullivan, Wu Xu, Li Qiang Zhang, Scott X. Mao,Nicholas S. Hudak, Xiao Hua Liu, Arunkumar Subramanian, Hongyou Fan, Liang Qi,Akihiro Kushima, and Ju Li Science 10 December 2010: 1515-1520. DOI: 10.1126/science.1198591

Reprinted with permission from AAAS.

Lithographic Patterning of α-MnO2 Nanowires On Glass

Lithographic Patterning of α-MnO2 Nanowires On Glass

R Penner Group (UCI) - Thrust A

Accomplishment

  • Lithographically patterned nanowire electrodeposition (LPNE) created high density, uniform, and long (mm-scale) nanowires in well-defined patterns, with adjustable width and height
  • LPNE couples relaxed top-down lithography with self-alignment of nanowires at patterned edges
  • Phase-pure α-MnO2 nanowires synthesized on glass by LPNE and verified by x-ray diffraction

Significance

  • LPNE method is broadly applicable to electrochemically deposited materials. It provides excellent control of nanowire geometry and surface area using simple lithography
  • LPNE enables high areal density of nanowire surfaces in well-defined patterns, with benefit to quality of characterization and to investigation of size-dependent behavior of electrochemical nanowires

Collaborators

Wenbo Yan, Yongan Yang, Reg Penner, UC Irvine Chemistry

Virus-Templated Silicon Anode for Li Ion Batteries

Virus-Templated Silicon Anode for Li Ion Batteries

CS Wang group (UMD) - Thrust B

Accomplishment

  • Assembly of a novel Si nanowire anode from Tobacco Mosaic Virus (TMV1cys) template
    • TMV's are identical nanotubes 300nm long, 4 nm ID, 18 nm OD
    • Self-assemble TMV on stainless steel through TMV 3' thiol group
    • Electroless deposition Ni current collector, then Si sputter deposition, onto TMV
    • Room temperature, neutral pH process
  • High capacities (3300mAh/g), nearly 10x capacity of graphite
  • Excellent charge-discharge cycling stability (0.20% loss per cycle at 1C), and consistent rate capabilities (46.4% at 4C) between 0 and 1.5 V

Significance

  • TMV provides precisely reproducible template for a nanostructured electrode, ideal for assessing the benefits of highly regular nanostructures
  • High capacity, comparable to other silicon nanostructured electrodes, demonstrates viability for TMV, biologically based nanoassembly strategy
  • TMV offers technology advantages: very lost cost, easily self-assembled on surfaces, highly reproducible nanostructures, in room temperature, neutral pH processes

Collaborators

Xilin Chen, Konstantinos Gerasopoulos, Juchen Guo, Adam Brown, Chunsheng Wang, Reza Ghodssi, James N. Culver

Supporting material

Xilin Chen et al, "Virus-Enabled Silicon Anode for Lithium-Ion Batteries", ACS Nano, Article ASAP (Aug. 13, 2010); DOI:10.1021/nn100963.

Redox Exchange Induced MnO2-Nanoparticle Enrichment in PEDOT Nanowires

Redox Exchange Induced MnO2-Nanoparticle Enrichment in PEDOT Nanowires

SB Lee Group (UMD) - Thrust A

Accomplishment

  • Synthesis of MnO2 nanoparticles (likely alpha) in PEDOT conductive polymer matrix, with control over nanoparticle size and ability to achieve uniform distribution in the PEDOT.
  • High electrochemical performance: very high specific capacitance (410 F/g) as the supercapacitor electrode materials as well as high Li ion storage capacity (300 mAh/g) as cathode materials of Li ion battery with good cyclability.
  • Revealed the mechanism of MnO2 nanoparticle formation in the PEDOT: triggered by the reduction of KMnO4 via the redox exchange of permanganate ions with the functional group 'S' on PEDOT.

Significance

  • Identified a new reaction pathway model to synthesize metal oxide nanoparticles in conductive polymer and graphitic carbon matrices.
  • Determined that the reaction primarily involves the S group on PEDOT, rather than the oxidized polymer backbone as previously believed
  • This synthesis route offers design flexibility to control and optimize MnO2 nanoparticle size for Li storage (insertion/desertion)

Collaborators

Ran Liu, Jonathon Duay, Zhe Gui, Stefanie Sherrill, Sung Kyoung Kim

Supporting Material

R. Liu, J. Duay, S.B. Lee. ACS Nano, 2010, 4 (7), pp 4299-4307. DOI: 10.1021/nn1010182

Predictions of Ethylene Carbonate Breakdown & Solid Electrolyte Interphase (SEI) Onset

Predictions of Ethylene Carbonate Breakdown & Solid Electrolyte Interphase (SEI) Onset

Kevin Leung (SNL) - Thrust C

Accomplishment

  • Computational methods predict the electrolyte decomposition products at an electrode-electrolyte interface during charging.
  • In the ab initio molecular dynamics model, two electrons transferring from LiC6 anode to ethylene carbonate-based electrolyte instigates breakdown.
  • Results indicate formation of CO and C2H4O22- reaction products, consistent with experiments1 but previously unpredicted by computation, as well as expected CO32- and C2H4 compounds.

Significance

  • The stability and safety of many electrochemical systems for electrical energy storage depend on a critical solid-electrolyte interphase (SEI), which forms from the reaction products and passivates the electrode layer.
  • The formation and character of the SEI layer is largely unclear.
  • This work is the first theoretical to address the initial chemical mechanisms of electrolyte breakdown at explicit electrode-liquid electrolyte interfaces and therefore SEI formation.

Collaborators

Kevin Leung (Sandia National Lab)
Joanne Budzien (Frostburg State)

Supporting Information

Leung & Budzien, Phys. Chem. Chem. Phys. 12, 6583 (2010)
1Onuki et al., JECS 155 A794 (2008).
2Lithium ion batteries: solid electrolyte interface, ed. Wang & Balbuena (Imperial College, London, 2004)

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Outer Wall Selectively Oxidized, Water-Soluble Double-Walled Carbon Nanotubes

Outer Wall Selectively Oxidized, Water-Soluble Double-Walled Carbon Nanotubes

YH Wang group (UMD) - Thrust B

Accomplishment

  • Selective oxidation of the outer wall of double-wall carbon nanotubes (DWCNTs) by oleum and nitric acid made the CNTs water soluble.
  • Inner wall remains intact, preserving CNT electrical conductivity properties. Outer wall is mostly functionalized, but intact regions enable contacts to inner walls.
  • Thin film conductivity of functionalized DWCNTs is up to 65% better than for SWCNTS

Significance

  • CNT benefits in conductivity are normally compromised by the functionalization often needed for nanoassembly and use of the CNTs
  • Two walls of DW-CNTs allows outer wall to be functionalized, providing for flexible design, assembly and use of CNT's in nanostructures, while retaining unique conductivity properties of CNTs

Collaborators

Brozena, A. H.; Moskowitz, J.; Shao, B.; Deng, S.-L.; Liao, H. W.; Gaskell, K. J.; Wang, Y. H.

Supporting material

Brozena, A. H.; Moskowitz, J.; Shao, B.; Deng, S.-L.; Liao, H. W.; Gaskell, K. J.; Wang, Y. H.* J. Am. Chem. Soc. 2010, 132, pp 3932-3938, DOI: 10.1021/ja910626u.

Electroosmotic Flow Rectification in Membranes with Asymmetric Nanopores - Demonstrating a 'Flow Diode'

Electroosmotic Flow Rectification in Membranes with Asymmetric Nanopores - Demonstrating a 'Flow Diode'

Charles Martin (UFL) - Thrust A

Accomplishment

A new electrokinetic phenomenon - electroosmotic flow rectification (EOF) - has been demonstrated.
  • EOF is a well-known electrokinetic phenomenon used to pump solutions through electrochemical devices.
  • We are studying EOF in nanopore membranes.
  • EOF rectification was demonstrated, for the first time, in mica membranes with pyramidally shaped nanopores (Figure 1 A).
  • One face of the membrane contains small openings (pore tips) and the other face has large pore openings (bases) (Figure 1 B).
  • This asymmetric pore shape, and the negative charge on the pore wall, are key to observing EOF rectification
When current passes through the nanopores:
  • EOF causes solution to be pumped through the membrane
  • With these asymmetric-pore membranes, the flow rate in one direction through the membrane is different than the flow rate in the opposite direction - EOF rectification (Figure 2)
  • Hence, the membrane is to flow what a diode is to current
  • he flow rate in the direction from base to tip is high and the flow rate from tip to base is low

Significance

  • A new electrokinetic phenomenon has been demonstrated and a first-order theoretical model was proposed.
  • The studies show the importance of surface charge and pore shape on the transport properties of nanopores, leading to a greater understanding of how confining electrolytes to nanopores affect transport properties in nanopore systems.
  • EOF measurements are also being used to quantitatively determine the surface charge density and a related parameter, the zeta potential.
  • Currently exploring electrochemical modulation of surface charge density.

Collaborators

Jin, P.; Mukaibo, H.; Horne, L. P.; Bishop, G. W.; Martin, C. R.

Reference

Leung & Budzien, Phys. Chem. Chem. Phys. 12, 6583 (2010)
J. Am. Chem. Soc. 2010, 132 (7), 2118-2119.