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ABSTRACT: High-performance and cost-effective rechargeable batteries are key to the success of electric vehicles and large-scale energy storage systems. Extensive research has focused on the development of (i) new high-energy electrodes that can store more lithium or (ii) high-power nano-structured electrodes hybridized with carbonaceous materials. However, the current status of lithium batteries based on redox reactions of heavy transition metals still remains far below the demands required for the proposed applications. Herein, we present a novel approach using tunable functional groups on graphene nano-platelets as redox centers. The electrode can deliver high capacity of ~250 mAh g(-1), power of ~20 kW kg(-1) in an acceptable cathode voltage range, and provide excellent cyclability up to thousands of repeated charge/discharge cycles. The simple, mass-scalable synthetic route for the functionalized graphene nano-platelets proposed in this work suggests that the graphene cathode can be a promising new class of electrode.
Scientific Reports 03/2013; 3:1506.
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ABSTRACT: Graphene-wrapped metal oxide hybrid materials are synthesized through inspiration from natural CO2 mineralization. We created hierarchical, nanostructured graphene/metal oxide by converting a CO2-mineralized graphene oxide/CaCO3 precursor to metal-based minerals such as graphene-wrapped CuO hybrid materials, which highly enhanced the stability and recyclability of the CuO anode for Li ion batteries. The synthesis of graphene-wrapped metal oxide and its application to Li ion battery electrodes suggest a new possibility for hybridizing graphene and metal oxide nanoparticles using the inspiration of natural mineralization.
Green Chemistry 09/2012; 14(9):2391-2394. · 6.32 Impact Factor
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ABSTRACT: The electrochemical properties of Na 3 V 2 (PO 4) 2 F 3 in a Na rechargeable battery were investigated through a combined computational and experimental study. Ex situ XRD results indicate that the reversible sodiation/desodiation occurs via one phase reaction and the structure of Na 3Àx V 2 (PO 4) 2 F 3 remains quite stable upon extraction and insertion of sodium. Notable is that the one phase reaction is accompanied by the negligible variation in lattice parameters ($1%) and unit cell volume ($2%) which results in a good cycle performance. It is further noticed that the desodiated phase is thermally stable up to 550 C implying the excellent safety characteristic of the charged electrode. The first principles calculations elucidate the mechanisms of the structural evolution and the electrochemical behavior of Na 3Àx V 2 (PO 4) 2 F 3 upon battery cycling.
Materials Chemistry 08/2012;
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ABSTRACT: With the move toward the use of greener materials for powered vehicles, environmentally-benign synthesis of energy materials is becoming important. Here, the energy storage capability of biominerals from the jaws of a marine bloodworm, Glycera dibranchiate, is demonstrated, implying the possibility of a bio-factory (or in vivo synthesis) for energy storage. Over the past decade, biomaterials have been extensively studied for medical applications, such as new pharmaceuticals, tissue engineer-ing, and artificial organs, due to their excellent biocompatibility. 1–4 Nowadays, biomaterials further expand their boundaries to various functionalities in semiconductors, sensors, and display devices. 5–10 Mimicking the structure and synthetic route of biomaterials in living organisms or direct use of the biomaterials often provides insights in enhancing the performance of devices due to similarities in the material requirements for functional devices and those of living organisms. The feasibility of biological materials as a template for the synthesis of energy storage materials has recently been investi-gated. 11–13 Pioneering works done by Nam et al. showed that organic biomolecules can be used as a structural template to provide growth sites for electrode materials in batteries. 11 In this study, Co 3 O 4 nanoparticles were grown onto genetically modified M13 viruses as templates, resulting in good electrochemical performance. In vitro synthesized, self-assembled peptides were also used as templates for the fabrication of battery electrodes. 14–16 Facile control of the peptide nanostructures by self-assembly could result in ideal electrode nanostructures for Li rechargeable batteries. Further evidence of this approach was reported by Ryu et al. who fabricated Fe phosphate electrode materials on peptide nanostructured templates by mimicking the natural biomineralization process of bone formation in which Ca phosphates form on collagen. 16 Recently, Chen et al. reported that a biomaterial itself can function as an active electrode for Li batteries. 17 Organic Li 2 C 6 O 6 extracted from biomass was capable of storing four Li ions, delivering a specific capacity of 580 mAh g 21 , which is substantially higher than that of conventional cathode materials (y170 mAh g 21). Such organic electrodes can potentially offer sustainable life cycles from production to consumption without generating additional CO 2 . Thus, the use of such chemistry is believed to be able to result in greener and more sustainable batteries. We envision that electrode materials can be produced from 'bio-factories,' once electrochemically active biomaterials are identified from the living organisms. Fig. 1 briefly illustrates the concept of the bio-factory. The living organisms that possess electrochemically active biominerals are farm-bred on a large scale. The biominerals are extracted for use in battery fabrication and the productivity of biominerals from the living organisms can be optimized by genetic engineering. The production of battery materials from bio-factories has several advantages over production from a 'real' factory, including environmental friendliness, non-toxicity to humans, non-necessity of large building sites, and potentially lower production
RSC Advances 07/2012; 2(13):5499-5501.
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ABSTRACT: New iron-based mixed-polyanion compounds Li(x)Na(4-x)Fe(3)(PO(4))(2)(P(2)O(7)) (x = 0-3) were synthesized, and their crystal structures were determined. The new compounds contained three-dimensional (3D)sodium/lithium paths supported by P(2)O(7) pillars in the crystal. First principles calculations identified the complex 3D paths with their activation barriers and revealed them as fast ionic conductors. The reversible electrode operation was found in both Li and Na cells with capacities of one-electron reaction per Fe atom, 140 and 129 mAh g(-1), respectively. The redox potential of each phase was ∼3.4 V (vs Li) for the Li-ion cell and ∼3.2 V (vs Na) for the Na-ion cell. The properties of high power, small volume change, and high thermal stability were also recognized, presenting this new compound as a potential competitor to other iron-based electrodes such as Li(2)FeP(2)O(7), Li(2)FePO(4)F, and LiFePO(4).
Journal of the American Chemical Society 06/2012; 134(25):10369-72. · 9.91 Impact Factor
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ABSTRACT: One-dimensional ZnMn2O4 nanowires have been prepared and investigated as anode materials in Li rechargeable batteries. The highly crystalline ZnMn2O4 nanowires about 15 nm in width and 500 nm in length showed a high specific capacity of about 650 mAh·g−1 at a current rate of 100 mA·g−1 after 40 cycles. They also exhibited high power capability at elevated current rates, i.e., 450 and 350 mAh·g−1 at current rates of 500 and 1000 mA·g−1, respectively. Formation of Mn3O4 and ZnO phases was identified by ex situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies after the initial discharge-charge cycle, which
indicates that the ZnMn2O4 phase was converted to a nanocomposite of Mn3O4 and ZnO phases immediately after the electrochemical conversion reaction.
KeywordsEnergy storage–lithium rechargeable battery–anode–ZnMn2O4
–nanowire
Nano Research 04/2012; 4(5):505-510. · 6.97 Impact Factor
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ABSTRACT: SnO2/graphene nanocomposites have been fabricated by a simple chemical method. In the fabrication process, the control of surface
charge causes echinoid-like SnO2 nanoparticles to be formed and uniformly decorated on the graphene. The electrostatic attraction between a graphene nanosheet
(GNS) and the echinoid-like SnO2 particles under controlled pH creates a unique nanostructure in which extremely small SnO2 particles are uniformly dispersed on the GNS. The SnO2/graphene nanocomposite has been shown to perform as a high capacity anode with good cycling behavior in lithium rechargeable
batteries. The anode retained a reversible capacity of 634 mA·h·g−1 with a coulombic efficiency of 98% after 50 cycles. The high reversibility can be attributed to the mechanical buffering
by the GNS against the large volume change of SnO2 during delithiation/lithiation reactions. Furthermore, the power capability is significantly enhanced due to the nanostructure,
which enables facile electron transport through the GNS and fast delithiation/lithiation reactions within the echinoid-like
nano-SnO2. The route suggested here for the fabrication of SnO2/graphene hybrid materials is a simple economical route for the preparation of other graphene-based hybrid materials which
can be employed in many different fields.
KeywordsGraphene-SnO2
-surface charge-nanocomposite-rechargeable batteries-lithium
Nano Research 04/2012; 3(11):813-821. · 6.97 Impact Factor
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ABSTRACT: Electrochemical properties of A(2)MnPO(4)F (A = Na/Li) were investigated both experimentally and with first principles calculations. A new Li(2)MnPO(4)F phase was successfully synthesized for the first time. A one alkali metal ion reaction occurred reversibly within a reasonable voltage window and a two alkali metal ion reaction took place at higher voltages.
Physical Chemistry Chemical Physics 02/2012; 14(10):3299-303. · 3.57 Impact Factor
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ABSTRACT: A Mn3O4/graphene hybrid material is fabricated using a facile and simple in-situ reduction process and shown to be a promising anode for lithium rechargeable batteries. The hybrid material retains a high capacity with a good cycle life of up to 990 mAh g−1 after 30 cycles. The excellent electrochemical performance is attributable to the unique nanostructure of the hybrid material. Highly crystalline Mn3O4 particles (20–30 nm) are uniformly dispersed on graphene whose high electronic conductivity and high surface area provide a conductive percolating network throughout the electrode in the hybrid material. The conductive graphene networks enhance an electron transfer in the electrode and promote the electrochemical activity of the crystalline Mn3O4.
Journal of Materials Research. 10/2011; 26(20):2665 - 2671.
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09/2011; , ISBN: 978-953-307-269-2
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ABSTRACT: An aliphatic thiol ligand of CuInS(2)/ZnS core/shell quantum dots is replaced with a hydroxyl-terminated thiol ligand by utilizing 'on-off state' of ligands during growth stage of the quantum dots. After the ligand-exchange, negligible differences were observed on both photoluminescence spectrum and luminescent quantum efficiency. The reason for the high retention of luminescent efficiency comes from no local agglomeration and no surface deterioration of QDs. It is also observed that 70% of initial ligands are exchanged by the replacing ligand, determined by FT-IR and (1)H NMR. The proposed method provides the quantum dots with an excellent dispersibility in polar solvents, supported by identical luminescence decay characteristics of the QDs.
Journal of Colloid and Interface Science 07/2011; 363(2):703-6. · 3.07 Impact Factor
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Advanced Materials 12/2010; 22(48):5537-41. · 13.88 Impact Factor
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ABSTRACT: Carbon nanotube (CNT)-amorphous FePO(4) core-shell nanowires are synthesized by aqueous solution-based mineralization through sequential adsorption of Fe(3+) and PO(4)(3-) ions onto the CNT surface. The hierarchical nanostructure with FePO(4) shell directly grown on the CNT core exhibits excellent electrochemical properties and performance as a cathode material for Li ion batteries.
Chemical Communications 10/2010; 46(39):7409-11. · 6.17 Impact Factor
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Advanced Materials 10/2010; 22(46):5260-4. · 13.88 Impact Factor
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ABSTRACT: The monodisperse spherical
core/shell particles were prepared by a heterogeneous precipitation coating of the phosphor shell on the surface of the core
particles. The shell thickness and the calculated crystallite size were increased with the core size and, thus, the photoluminescence
(PL) intensity was also increased. The phosphor photonic crystals (PCs) were fabricated by self-assembly of the core/shell
particles. The PL intensity of the phosphor PCs was higher by around 2.0 times than that of the randomly stacked reference
sample due to the high packing density and quality. The suppression of the PL emission peaks by the overlap with the stopband
and the enhancement of the emission peak at the blue edge of the stopband were observed. The color purity of the phosphor
PCs was definitely improved by the design of the stopband position.
Journal of The Electrochemical Society. 09/2010; 157(10):J358-J363.
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ABSTRACT: We report the Mn based olivine electrode material with high power and energy. Easier and more frequent nucleation by Fe and Co in Mn-based olivines significantly enhanced the rate capability as evidenced by the electrochemical results.
Chemical Communications 02/2010; 46(8):1305-7. · 6.17 Impact Factor
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ABSTRACT: We report the synthesis of novel diphenylalanine/cobalt(II,III) oxide (Co(3)O(4)) composite nanowires by peptide self-assembly. Peptide nanowires were prepared by treating amorphous diphenylalanine film with aniline vapor at an elevated temperature. They were hybridized with Co(3)O(4) nanocrystals through the reduction of cobalt ions in an aqueous solution using sodium borohydride (NaBH(4)) without any complex processes such as heat treatment. The formation of peptide/Co(3)O(4) composite nanowires was characterized using multiple tools, such as electron microscopies and elemental analysis, and their potential application as a negative electrode for Li-ion batteries was explored by constructing Swagelok-type cells with hybrid nanowires as a working electrode and examining their charge/discharge behavior. The present study provides a useful approach for the synthesis of functional metal oxide nanomaterials by demonstrating the feasibility of peptide/Co(3)O(4) hybrid nanowires as an energy storage material.
ACS Nano 12/2009; 4(1):159-64. · 10.77 Impact Factor
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ABSTRACT: The electrochemical properties and phase stability of the multi-component olivine compound LiMn1/3Fe1/3Co1/3PO4 are studied experimentally and with first-principles calculation. The formation of a solid solution between LiMnPO4, LiFePO4, and LiCoPO4 at this composition is confirmed by XRD patterns and the calculated energy. The experimental and first-principle results indicate that there are three distinct regions in the electrochemical profile at quasi-open-circuit circuit potentials of similar to 3.5V, similar to 4.1V, and similar to 4.7V, which are attributed 50 Fe3+/Fe-2+,Fe- , Mn3+/Mn2+, and Co3+/Co2+ redox couples, respectively. However, exceptionally large polarization is observed only for the region near 4.1V of Mn3+/Mn2+ redox couples, implying; an intrinsic charge transfer problem. An ex situ XRD study reveals that the reversible one-phase reaction of Li extraction/insertion mechanism prevails, unexpectedly, for all lithium compositions of LixMn1/3Fe1/3Co1/3PO4 (0 <= x <= 1) at room temperature. This is the first demonstration that the well-ordered non-nanocrystalline (less than 1% Li-M disorder and a few hundred nanometer size particle) olivine electrode can be operated solely in a one-phase mode.
Advanced Functional Materials 08/2009; 19(20):3285 - 3292. · 10.18 Impact Factor
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ABSTRACT: The three-dimensional network of TiO(2) hollow nanoribbons designed from a peptide assembly using atomic layer deposition is demonstrated as a promising Li secondary battery electrode in this study. The nanoribbon network ensures effective transport of electrons and Li ions due to (i) a well-connected network of nanoribbons and (ii) the hollow structure of each nanoribbon itself, into which Li ions in the electrolyte can readily diffuse. The improved specific capacity, rate capability, and cyclability of the nanonetwork show that the utilization of a nanonetwork of individual hollow ribbons can serve as a promising strategy toward the development of high-performance electrode for Li secondary batteries.
ACS Nano 05/2009; 3(5):1085-90. · 10.77 Impact Factor
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ABSTRACT: Luminescence films were prepared by infiltration of the tris(dibenzoylmethane) mono(1, 10-phenanthroline) europium incorporated ormosil into colloidal SiO(2) photonic crystal templates. Because a stopband of the template was not overlapped with the PL excitation and emission bands, the stopband did not suppress the PL intensity. The PL intensity of the infiltrated film into the template was about 13.1 times higher than that of the plane film prepared without the template. Three major terms, which are the mass term, the scattering term, and the crystallinity term, were considered as factors that improve the PL intensity. The relative ratio of the effects of the mass term : the scattering term : the crystallinity term was 2.1 : 2.8 : 2.2.
Optics Express 04/2009; 17(5):3732-40. · 3.59 Impact Factor
