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1.
Nanoscale Horiz ; 2020 Feb 13.
Artigo em Inglês | MEDLINE | ID: mdl-32053127

RESUMO

Spatial confinement is a desirable successful strategy to trap sulfur within its porous host and has been widely applied in lithium-sulfur (Li-S) batteries. However, physical confinement alone is currently not enough to reduce the lithium polysulfide (Li2Sn, 4 ≤ n ≤ 8, LIPSs) shuttle effect with sluggish LIPS-dissolving kinetics. In this work, we have integrated spatial confinement with a polar catalyst, and designed a three-dimensional (3D) interconnected, Co decorated and N doped porous carbon nanofiber (Co/N-PCNF) network. This Co/N-PCNF film serves as a freestanding host for sulfur trapping, which could effectively facilitate the infiltration of electrolyte and electron transport. In addition, the polar Co species possess strong chemisorption with LIPSs, catalyzing their reaction kinetics as well. As a result of this rational design and integration, the Co/N-PCNF@S cathode with a sulfur loading of 2 mg cm-2 exhibits a high initial discharge capacity of 878 mA h g-1 at 1C, and maintains a discharge capacity of 728 mA h g-1 after 200 cycles. Even with high sulfur loading of 9.33 mg cm-2, the cathode still keeps a stable areal capacity of 7.16 mA h cm-2 at 0.2C after 100 cycles, which is much higher than the current areal capacity (4 mA h cm-2) of commercialized lithium-ion batteries (LIBs). This rational design may provide a new approach for future development of high-density Li-S batteries with high sulfur loading.

2.
Artigo em Inglês | MEDLINE | ID: mdl-31961644

RESUMO

As a parent compound of Li-rich electrodes, Li2MnO3 exhibits high capacity during the initial charge; however, it suffers notoriously low Coulombic efficiency due to oxygen and surface activities. Here, we successfully optimize the oxygen activities toward reversible oxygen redox reactions by intentionally introducing protons into lithium octahedral vacancies in the Li2MnO3 system with its original structural integrity maintained. Combining structural probes, theoretical calculations, and resonant inelastic X-ray scattering results, a moderate coupling between the introduced protons and lattice oxygen at the oxidized state is revealed, which stabilizes the oxygen activities during charging. Such a coupling leads to an unprecedented initial Coulombic efficiency (99.2%) with a greatly improved discharge capacity of 302 mAh g-1 in the protonated Li2MnO3 electrodes. These findings directly demonstrate an effective concept for controlling oxygen activities in Li-rich systems, which is critical for developing high-energy cathodes in batteries.

3.
Nanoscale Res Lett ; 14(1): 288, 2019 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-31428881

RESUMO

In this paper, the structural, electronic, and optical properties of MoS2 multilayers are investigated by employing the first-principles method. Up to six-layers of MoS2 have been comparatively studied. The covalency and ionicity in the MoS2 monolayer are shown to be stronger than those in the bulk. As the layer number is increased to two or above two, band splitting is significant due to the interlayer coupling. We found that long plateaus emerged in the imaginary parts of the dielectric function [Formula: see text] and the joint density of states (JDOS) of MoS2 multilayers, due to the Van Hove singularities in a two-dimensional material. One, two and three small steps appear at the thresholds of both the long plateau of [Formula: see text] and JDOS, for monolayer, bilayer, and trilayer, respectively. As the number of layers further increased, the number of small steps increases and the width of the small steps decreases accordingly. Due to interlayer coupling, the longest plateau and shortest plateau of JDOS are from the monolayer and bulk, respectively.

4.
Angew Chem Int Ed Engl ; 57(37): 11918-11923, 2018 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-30040187

RESUMO

Na2 FePO4 F is a promising cathode material for Na-ion batteries owing to its relatively high discharge voltage and excellent cycling performance. Now, the long- and short-range structural evolution of Na2 FePO4 F during cycling is studied by in situ high-energy X-ray diffraction (XRD), ex situ solid-state nuclear magnetic resonance (NMR), and first-principles DFT calculations. DFT calculations suggest that the intermediate phase, Na1.5 FePO4 F, adopts the space group of P21 /c, which is a subgroup (P21 /b11, No. 14) of Pbcn (No. 60), the space group of the starting phase, Na2 FePO4 F, and this space group provides a good fit to the experimental XRD and NMR results. The two crystallographically unique Na sites in the structure of Na2 FePO4 F behave differently during cycling, where the Na ions on the Na2 site are electrochemically active while those on the Na1 site are inert. This study determines the structural evolution and the electrochemical reaction mechanisms of Na2 FePO4 F in a Na-ion battery.

5.
Nanoscale Res Lett ; 13(1): 199, 2018 Jul 06.
Artigo em Inglês | MEDLINE | ID: mdl-29978266

RESUMO

The electronic properties of vanadium atoms adsorbed on clean and graphene-covered Cu(111) surface have been systematically studied using ab initio theoretical method. Two coverages (1/9 ML and 1 ML) of vanadium adsorption are considered in this work. Our calculations indicate that V staying underneath the Cu surface is found to be the most stable adsorption site at the aforementioned two coverages for V/Cu(111). However, such adsorption may lead to undesired properties. Therefore, we introduce graphene as a buffer layer to effectively alleviate the direct interaction between V and Cu surface. The calculations show that electronic properties of the original graphene layer are significantly affected by the interactions of C atoms with the V adatoms; the Dirac point of graphene is "destroyed" as a consequence at both coverages. In the V/Gra/Cu(111) system, the interaction between graphene layer and the substrate Cu atoms remains weak as in the Gra/Cu(111) system. Moreover, a relatively low coverage of 1/9 ML gives rise to a spin-polarized system while a non-spin-polarized system is observed at the coverage of 1 ML. This finding offers a new way for the application of vanadium-based materials in reality.

6.
Phys Chem Chem Phys ; 20(21): 14557-14563, 2018 May 30.
Artigo em Inglês | MEDLINE | ID: mdl-29766162

RESUMO

Structural phase transitions of electrode materials are responsible for poor reversibility during charge/discharge cycling in Li-ion batteries. Using previously developed structural databases, we investigate a structural landscape for LixFeSiO4 systems at x = 1. Starting with low-energy Li2FeSiO4 crystal structures, we explore the crystal structures of the material in different states of charge. The as-prepared Li2FeSiO4 materials adopt low energy structures characterized by two-dimensional (2D) Fe-Si networks. After the removal of one Li per formula unit to form LiFeSiO4, the structures with three-dimensional (3D) diamond-like Fe-Si networks become more energetically favorable without a significant impact on the charge capacity, which agrees with previous experimental and theoretical work. However, we reveal that the structure with a 3D diamond-like Fe-Si network can further transform into a new structure at x = 1. And the Li atom is hard to reinsert into these new structures. Consequently the system is prevented from returning to the Li2FeSiO4 state. We believe that the formation of this new structure plays an important role in the loss of reversible capacity of Li2FeSiO4 electrode materials.

7.
J Am Chem Soc ; 139(29): 9771-9774, 2017 07 26.
Artigo em Inglês | MEDLINE | ID: mdl-28693318

RESUMO

We report the discovery of a dramatically enhanced N2 electroreduction reaction (NRR) selectivity under ambient conditions via the Li+ incorporation into poly(N-ethyl-benzene-1,2,4,5-tetracarboxylic diimide) (PEBCD) as a catalyst. The detailed electrochemical evaluation and density functional theory calculations showed that Li+ association with the O atoms in the PEBCD matrix can retard the HER process and can facilitate the adsorption of N2 to afford a high potential scope for the NRR process to proceed in the "[O-Li+]·N2-Hx" alternating hydrogenation mode. This atomic-scale incorporation strategy provides new insight into the rational design of NRR catalysts with higher selectivity.

8.
ACS Nano ; 11(4): 4217-4224, 2017 04 25.
Artigo em Inglês | MEDLINE | ID: mdl-28358508

RESUMO

Intercalation-type TiNbxO2+2.5x (x = 2, 5, and 24) anode materials have recently become more interesting for lithium-ion batteries (LIBs) due to their large theoretical capacities of 388-402 mAh g-1. However, the Ti4+/Nb5+ ions in TiNbxO2+2.5x with empty 3d/4d orbitals usually lead to extremely low electronic conductivity of <10-9 S cm-1, greatly restricting their practical capacity and rate capability. Herein, we report a class of highly conductive Cr0.5Nb24.5O62 nanowires as an intercalation-type anode material for high-performance LIBs. The as-made Cr0.5Nb24.5O62 nanowires show an open shear ReO3 crystal structure (C2 space group) with 4% tetrahedra and a conducting characteristic with ultrahigh electronic conductivity of 3.6 × 10-2 S cm-1 and a large Li+-ion diffusion coefficient of 2.19 × 10-13 cm2 s-1. These important characteristics make them deliver outstanding electrochemical properties in term of the largest reversible capacity (344 mAh g-1 at 0.1 C) in all the known niobium- and titanium-based anode materials, safe working potential (∼1.65 V vs Li/Li+), high first-cycle Coulombic efficiency (90.8%), superior rate capability (209 mAh g-1 at 30 C), and excellent cycling stability, making them among the best for LIBs in niobium- and titanium-based anode materials.

9.
ACS Appl Mater Interfaces ; 8(27): 17233-8, 2016 Jul 13.
Artigo em Inglês | MEDLINE | ID: mdl-27305627

RESUMO

A new cubic polymorph of sodium iron silicate, Na2FeSiO4, is reported for the first time as a cathode material for Na-ion batteries. It adopts an unprecedented cubic rigid tetrahedral open framework structure, i.e., F4̅3m, leading to a polyanion cathode material without apparent cell volume change during the charge/discharge processes. This cathode shows a reversible capacity of 106 mAh g(-1) and a capacity retention of 96% at 5 mA g(-1) after 20 cycles.

10.
Sci Rep ; 5: 17836, 2015 Dec 03.
Artigo em Inglês | MEDLINE | ID: mdl-26632883

RESUMO

To explore anode materials with large capacities and high rate performances for the lithium-ion batteries of electric vehicles, defective Ti2Nb10O27.1 has been prepared through a facile solid-state reaction in argon. X-ray diffractions combined with Rietveld refinements indicate that Ti2Nb10O27.1 has the same crystal structure with stoichiometric Ti2Nb10O29 (Wadsley-Roth shear structure with A2/m space group) but larger lattice parameters and 6.6% O(2-) vacancies (vs. all O(2-) ions). The electronic conductivity and Li(+)ion diffusion coefficient of Ti2Nb10O27.1 are at least six orders of magnitude and ~2.5 times larger than those of Ti2Nb10O29, respectively. First-principles calculations reveal that the significantly enhanced electronic conductivity is attributed to the formation of impurity bands in Ti2Nb10O29-x and its conductor characteristic. As a result of the improvements in the electronic and ionic conductivities, Ti2Nb10O27.1 exhibits not only a large initial discharge capacity of 329 mAh g(-1) and charge capacity of 286 mAh g(-1) at 0.1 C but also an outstanding rate performance and cyclability. At 5 C, its charge capacity remains 180 mAh g(-1) with large capacity retention of 91.0% after 100 cycles, whereas those of Ti2Nb10O29 are only 90 mAh g(-1) and 74.7%.

11.
Sci Rep ; 5: 15555, 2015 Oct 26.
Artigo em Inglês | MEDLINE | ID: mdl-26497381

RESUMO

Using a motif-network search scheme, we studied the tetrahedral structures of the dilithium/disodium transition metal orthosilicates A2MSiO4 with A = Li or Na and M = Mn, Fe or Co. In addition to finding all previously reported structures, we discovered many other different tetrahedral-network-based crystal structures which are highly degenerate in energy. These structures can be classified into structures with 1D, 2D and 3D M-Si-O frameworks. A clear trend of the structural preference in different systems was revealed and possible indicators that affect the structure stabilities were introduced. For the case of Na systems which have been much less investigated in the literature relative to the Li systems, we predicted their ground state structures and found evidence for the existence of new structural motifs.

12.
Sci Rep ; 5: 14196, 2015 Sep 16.
Artigo em Inglês | MEDLINE | ID: mdl-26374077

RESUMO

For topological insulators to be implemented in practical applications, it is a prerequisite to select suitable substrates that are required to leave insulators' nontrivial properties and sizable opened band gaps (due to spin-orbital couplings) unaltered. Using ab initio calculations, we predict that Ge(111) surface qualified as a candidate to support stanene sheets, because the band structure of √3 × âˆš3 stanene/Ge(111) (2 × 2) surface displays a typical Dirac cone at Γ point in the vicinity of the Fermi level. Aided with the result of Z2 invariant calculations, a √3 × âˆš3 stanene/Ge(111) (2 × 2) system has been proved to sustain the nontrivial topological phase, with the prove being confirmed by the edge state calculations of stanene ribbons. This finding can serve as guidance for epitaxial growth of stanene on substrate and render stanene feasible for practical use as a topological insulator.

13.
ChemSusChem ; 7(12): 3328-33, 2014 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-25354020

RESUMO

Nanorod-like CuS and Cu2 S have been fabricated by a hydrothermal approach without using any surfactant and template. The electrochemical behavior of CuS and Cu2 S nanorod anodes for lithium-ion batteries reveal that they exhibit stable lithium-ion insertion/extraction reversibility and outstanding rate capability. Both of the electrodes exhibit excellent capacity retentions irrespective of the rate used, even at a high current density of 3200 mA g(-1) . More than 370 mAh g(-1) can be retained for the CuS electrode and 260 mAh g(-1) for the Cu2 S electrode at the high current rate. After 100 cycles at 100 mA g(-1) , the obtained CuS and Cu2 S electrodes show discharge capacities of 472 and 313 mAh g(-1) with retentions of 92% and 96%, respectively. Together with the simplicity of fabrication and good electrochemical properties, CuS and Cu2 S nanorods are promising anode materials for practical use the next-generation lithium-ion batteries.


Assuntos
Fontes de Energia Elétrica , Eletrodos , Lítio , Nanotubos , Sulfetos/síntese química , Cobre , Microscopia Eletrônica de Varredura , Microscopia Eletrônica de Transmissão , Tensoativos , Difração de Raios X
14.
Nanoscale Res Lett ; 9(1): 110, 2014 Mar 08.
Artigo em Inglês | MEDLINE | ID: mdl-24606964

RESUMO

Superlattice provides a new approach to enrich the class of materials with novel properties. Here, we report the structural and electronic properties of superlattices made with alternate stacking of two-dimensional hexagonal germanene (or silicene) and a MoS2 monolayer using the first principles approach. The results are compared with those of graphene/MoS2 superlattice. The distortions of the geometry of germanene, silicene, and MoS2 layers due to the formation of the superlattices are all relatively small, resulting from the relatively weak interactions between the stacking layers. Our results show that both the germanene/MoS2 and silicene/MoS2 superlattices are manifestly metallic, with the linear bands around the Dirac points of the pristine germanene and silicene seem to be preserved. However, small band gaps are opened up at the Dirac points for both the superlattices due to the symmetry breaking in the germanene and silicene layers caused by the introduction of the MoS2 sheets. Moreover, charge transfer happened mainly within the germanene (or silicene) and the MoS2 layers (intra-layer transfer), as well as some part of the intermediate regions between the germanene (or silicene) and the MoS2 layers (inter-layer transfer), suggesting more than just the van der Waals interactions between the stacking sheets in the superlattices.

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