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1.
ACS Appl Mater Interfaces ; 11(47): 44204-44213, 2019 Nov 27.
Artigo em Inglês | MEDLINE | ID: mdl-31692322

RESUMO

The solid electrolyte interphase (SEI) layer plays an important role in altering the ion transport and modifying the structural evolution of the Li metal anode during repeated cycling. While the fundamental understanding of the SEI properties has been continuously advanced in recent years, effectively tuning the SEI components, especially the inorganic constituents, is still challenging. In this work, tungsten trioxide, WO3, is found to promote the formation of inorganic salts, for example, LiF/Li2CO3 in SEI layers, thereby enhancing the SEI properties such as mechanical and chemical stabilities. Additionally, WO3 is simultaneously reduced to electronic W nanoparticles during the electrochemical process, mitigating the formation of "dead" Li, which otherwise is completely wrapped by the accumulated insulating SEI layers. The possibility of WO3 in catalyzing electrolyte decomposition, through favored reaction pathway, to produce robust SEI layers is discussed. This work provides new insights into the control of the SEI properties on Li metal surfaces.

2.
Langmuir ; 35(50): 16459-16465, 2019 Dec 17.
Artigo em Inglês | MEDLINE | ID: mdl-31714091

RESUMO

Lithium metal has great potential to become the anode for the next generation of high-energy-density batteries because of high capacity (3860 mAh g-1), lowest negative electrochemical potential, and low density. Low cycle efficiency and dendrite growth are two critical barriers for rechargeable batteries using Li metal as the anode, mainly due to the coupled mechanical/chemical degradation of the solid electrolyte interphase (SEI) layer formed on the Li metal surface. In this work, we found that a composite film of lithium aryl silanolate with uniformly distributed submicron LiCl-dominant particles can in situ form on the Li metal surface by treating Li with a single phenyl substituted chlorosilane. The synergistic effect of the high modulus of the composite film resulted from both well-dispersed LiCl particles and phenyl ring structures, and the extra reinforcement by the π-π interaction of aryl silanolate molecules that coated on LiCl particles and Li electrode surface endows the artificial surface coating film with high modulus and stability, and, thus, suitable as an artificial SEI layer. The coin cells using the lithium metal electrodes with this Lithium silanolate/LiCl particle composite coating layer showed an improved cycle efficiency and the extended life in a relatively harsh cycling condition.

3.
J Phys Chem Lett ; 9(18): 5508-5514, 2018 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-30198721

RESUMO

Understanding the solid electrolyte interphase (SEI) formation mechanism is critically important for the performance and durability of lithium-ion batteries. However, the details of how SEI builds up into a nanometer-thick layer from molecular level reduction reactions on negative electrodes are missing. Here, isotope-assisted time-of-flight secondary ion mass spectrometry analyses were designed to answer this fundamental question. By investigating the isotope ratio profile in SEI during the initial SEI formation cycle, it is discovered that the topmost SEI near the electrolyte formed first and the SEI near the electrode formed later. This new "bottom-up" SEI growth mechanism was then correlated to the electrolyte one-electron and two-electron reduction reaction dynamics, which in turn explains the formation of the two-layered organic-inorganic SEI composite structure.

4.
Small ; 14(8)2018 02.
Artigo em Inglês | MEDLINE | ID: mdl-29356411

RESUMO

Silicon has been intensively studied as an anode material for lithium-ion batteries (LIB) because of its exceptionally high specific capacity. However, silicon-based anode materials usually suffer from large volume change during the charge and discharge process, leading to subsequent pulverization of silicon, loss of electric contact, and continuous side reactions. These transformations cause poor cycle life and hinder the wide commercialization of silicon for LIBs. The lithiation and delithiation behaviors, and the interphase reaction mechanisms, are progressively studied and understood. Various nanostructured silicon anodes are reported to exhibit both superior specific capacity and cycle life compared to commercial carbon-based anodes. However, some practical issues with nanostructured silicon cannot be ignored, and must be addressed if it is to be widely used in commercial LIBs. This Review outlines major impactful work on silicon-based anodes, and the most recent research directions in this field, specifically, the engineering of silicon architectures, the construction of silicon-based composites, and other performance-enhancement studies including electrolytes and binders. The burgeoning research efforts in the development of practical silicon electrodes, and full-cell silicon-based LIBs are specially stressed, which are key to the successful commercialization of silicon anodes, and large-scale deployment of next-generation high energy density LIBs.

5.
ACS Appl Mater Interfaces ; 9(34): 28406-28417, 2017 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-28770982

RESUMO

The chemical and mechanical stability of SEI layers are particularly important for high capacity anode materials such as silicon, which undergoes large volume changes (∼300%) during cycling. In this work, we present a novel approach for applying controlled strains to SEI films with patterned Si electrodes to systematically investigate the impact of large volume changes on SEI formation and evolution. Comparisons between patterned silicon islands and continuous silicon thin films make it possible to correlate the irreversible capacity losses due to expansion and contraction of underlying silicon. The current work demonstrates that strain in the SEI layer leads to more lithium consumption. The combination of in situ AFM and electrochemical lithium loss measurements provides further information on SEI layer growth. These experiments indicate that in-plane strains in the SEI layer lead to substantial increases in the amount of inorganic phase formation, without significantly affecting the overall SEI thickness. These observations are further supported with EIS and TOF-SIMS results. A map of irreversible capacity evolution with strain in the SEI is obtained from the experimental results.

6.
ACS Appl Mater Interfaces ; 9(24): 20603-20612, 2017 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-28557416

RESUMO

Tuned chalcogenide single crystals rooted in sulfur-doped graphene were prepared by high-temperature solution chemistry. We present a facile route to synthesize a rod-on-sheet-like nanohybrid as an active anode material and demonstrate its superior performance in lithium ion batteries (LIBs). This nanohybrid contains a nanoassembly of one-dimensional (1D) single-crystalline, orthorhombic SnS onto two-dimensional (2D) sulfur-doped graphene. The 1D nanoscaled SnS with the rodlike single-crystalline structure possesses improved transport properties compared to its 2D hexagonal platelike SnS2. Furthermore, we blend this hybrid chalcogenide with biodegradable polymer composite using water as a solvent. Upon drying, the electrodes were subjected to heating in vacuum at 150 °C to induce polymer condensation via formation of carboxylate groups to produce a mechanically robust anode. The LIB using the as-developed anode material can deliver a high volumetric capacity of ∼2350 mA h cm-3 and exhibit superior cycle stability over 1500 cycles as well as a high capacity retention of 85% at a 1 C rate. The excellent battery performance combined with the simplistic, scalable, and green chemistry approach renders this anode material as a very promising candidate for LIB applications.

7.
ACS Appl Mater Interfaces ; 9(11): 9551-9558, 2017 Mar 22.
Artigo em Inglês | MEDLINE | ID: mdl-27808493

RESUMO

A novel self-supported electrode with long cycling life and high mass loading was developed based on carbon-coated Si nanowires grown in situ on highly conductive and flexible carbon fabric substrates through a nickel-catalyzed one-pot atmospheric pressure chemical vapor deposition. The high-quality carbon coated Si nanowires resulted in high reversible specific capacity (∼3500 mA h g-1 at 100 mA g-1), while the three-dimensional electrode's unique architecture leads to a significantly improved robustness and a high degree of electrode stability. An exceptionally long cyclability with a capacity retention of ∼66% over 500 cycles at 1.0 A g-1 was achieved. The controllable high mass loading enables an electrode with extremely high areal capacity of ∼5.0 mA h cm-2. Such a scalable electrode fabrication technology and the high-performance electrodes hold great promise in future practical applications in high energy density lithium-ion batteries.

8.
ACS Appl Mater Interfaces ; 8(8): 5687-93, 2016 Mar 02.
Artigo em Inglês | MEDLINE | ID: mdl-26852871

RESUMO

Understanding of the electrical conduction, that is, ionic and electronic conduction, through the solid electrolyte interphase (SEI) is critical to the design of durable lithium-ion batteries (LIBs) with high rate capability and long life. It is believed that an ideal SEI should not only be an ionic conductor, but also an electronic insulator. In this study, we present a theoretical design of an artificial SEI consisting of lithium fluoride (LiF) and lithium carbonate (Li2CO3) on a LIB anode based on a newly developed density functional theory (DFT) informed space charge model. We demonstrate that the migration of lattice Li ions from LiF phase to form Li interstitials in Li2CO3 is energetically favorable near the LiF/Li2CO3 interface. At equilibrium, this interfacial defect reaction establishes a space charge potential across the interface, which causes the accumulation of ionic carriers but the depletion of electronic carriers near the LiF/Li2CO3 interface. To utilize this space charge effect, we propose a computationally designed, nanostructured artificial SEI structure with high density of interfaces of LiF and Li2CO3 perpendicular to the electrode. On the basis of this structure, the influences of grain size and volume ratio of the two phases were studied. Our results reveal that reducing the grain size of Li2CO3 in the nanostructured composite can promote ionic carriers and increase the ionic conductivity through the composite SEI by orders of magnitude. At the same time, the electronic conductivity is reduced due to electron depletion near the LiF/Li2CO3 interface. Furthermore, an optimal volume fraction that ensures high ionic and low electronic conduction was predicted.

9.
Nano Lett ; 16(3): 2011-6, 2016 Mar 09.
Artigo em Inglês | MEDLINE | ID: mdl-26889564

RESUMO

The solid electrolyte interphase (SEI), a passivation layer formed on electrodes, is critical to battery performance and durability. The inorganic components in SEI, including lithium carbonate (Li2CO3) and lithium fluoride (LiF), provide both mechanical and chemical protection, meanwhile control lithium ion transport. Although both Li2CO3 and LiF have relatively low ionic conductivity, we found, surprisingly, that the contact between Li2CO3 and LiF can promote space charge accumulation along their interfaces, which generates a higher ionic carrier concentration and significantly improves lithium ion transport and reduces electron leakage. The synergetic effect of the two inorganic components leads to high current efficiency and long cycle stability.

10.
Phys Chem Chem Phys ; 18(5): 3706-15, 2016 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-26760786

RESUMO

Surface coatings as artificial solid electrolyte interphases have been actively pursued as an effective way to improve the cycle efficiency of nanostructured Si electrodes for high energy density lithium ion batteries, where the mechanical stability of the surface coatings on Si is as critical as Si itself. However, the chemical composition and mechanical property change of coating materials during the lithiation and delithiation process imposed a grand challenge to design coating/Si nanostructure as an integrated electrode system. In our work, we first developed reactive force field (ReaxFF) parameters for Li-Si-Al-O materials to simulate the lithiation process of Si-core/Al2O3-shell and Si-core/SiO2-shell nanostructures. With reactive dynamics simulations, we were able to simultaneously track and correlate the lithiation rate, compositional change, mechanical property evolution, stress distributions, and fracture. A new mechanics model based on these varying properties was developed to determine how to stabilize the coating with a critical size ratio. Furthermore, we discovered that the self-accelerating Li diffusion in Al2O3 coating forms a well-defined Li concentration gradient, leading to an elastic modulus gradient, which effectively avoids local stress concentration and mitigates crack propagation. Based on these results, we propose a modulus gradient coating, softer outside, harder inside, as the most efficient coating to protect the Si electrode surface and improve its current efficiency.

11.
Nat Commun ; 6: 8844, 2015 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-26538181

RESUMO

Silicon has been identified as a highly promising anode for next-generation lithium-ion batteries (LIBs). The key challenge for Si anodes is large volume change during the lithiation/delithiation cycle that results in chemomechanical degradation and subsequent rapid capacity fading. Here we report a novel fabrication method for hierarchically porous Si nanospheres (hp-SiNSs), which consist of a porous shell and a hollow core. On charge/discharge cycling, the hp-SiNSs accommodate the volume change through reversible inward Li breathing with negligible particle-level outward expansion. Our mechanics analysis revealed that such inward expansion is enabled by the much stiffer lithiated layer than the unlithiated porous layer. LIBs assembled with the hp-SiNSs exhibit high capacity, high power and long cycle life, which is superior to the current commercial Si-based anode materials. The low-cost synthesis approach provides a new avenue for the rational design of hierarchically porous structures with unique materials properties.

12.
ACS Appl Mater Interfaces ; 7(44): 24895-901, 2015 Nov 11.
Artigo em Inglês | MEDLINE | ID: mdl-26496231

RESUMO

Reduced graphene oxides loaded with tin-antimony alloy (RGO-SnSb) nanocomposites were synthesized through a hydrothermal reaction and the subsequent thermal reduction treatments. Transmission electron microscope images confirm that SnSb nanoparticles with an average size of about 20-30 nm are uniformly dispersed on the RGO surfaces. When they were used as anodes for rechargeable sodium (Na)-ion batteries, these as-synthesized RGO-SnSb nanocomposite anodes delivered a high initial reversible capacity of 407 mAh g(-1), stable cyclic retention for more than 80 cycles and excellent cycle stability at ultra high charge/discharge rates up to 30C. The significantly improved performance of the synthesized RGO-SnSb nanocomposites as Na-ion battery anodes can be attributed to the synergetic effects of RGO-based flexible framework and the nanoscale dimension of the SnSb alloy particles (<30 nm). Nanosized intermetallic SnSb compounds can exhibit improved structural stability and conductivity during charge and discharge reactions compared to the corresponding individuals (Sn and Sb particles). In the meantime, RGO sheets can tightly anchor SnSb alloy particles on the surfaces, which can not only effectively suppress the agglomeration of SnSb particles but also maintain excellent electronic conduction. Furthermore, the mechanical flexibility of the RGO phase can accommodate the volume expansion and contraction of SnSb particles during the prolonged cycling, therefore, improve the electrode integrity mechanically and electronically. All of these contribute to the electrochemical performance improvements of the RGO-SnSb nanocomposite-based electrodes in rechargeable Na-ion batteries.

13.
Nat Commun ; 6: 8597, 2015 Oct 26.
Artigo em Inglês | MEDLINE | ID: mdl-26497228

RESUMO

Silicon has the potential to revolutionize the energy storage capacities of lithium-ion batteries to meet the ever increasing power demands of next generation technologies. To avoid the operational stability problems of silicon-based anodes, we propose synergistic physicochemical alteration of electrode structures during their design. This capitalizes on covalent interaction of Si nanoparticles with sulfur-doped graphene and with cyclized polyacrylonitrile to provide a robust nanoarchitecture. This hierarchical structure stabilized the solid electrolyte interphase leading to superior reversible capacity of over 1,000 mAh g(-1) for 2,275 cycles at 2 A g(-1). Furthermore, the nanoarchitectured design lowered the contact of the electrolyte to the electrode leading to not only high coulombic efficiency of 99.9% but also maintaining high stability even with high electrode loading associated with 3.4 mAh cm(-2). The excellent performance combined with the simplistic, scalable and non-hazardous approach render the process as a very promising candidate for Li-ion battery technology.

14.
J Am Chem Soc ; 137(43): 13732-5, 2015 Nov 04.
Artigo em Inglês | MEDLINE | ID: mdl-26477353

RESUMO

The intercalation compounds are generally considered as ideal electrode materials for lithium-ion batteries thanks to their minimum volume expansion and fast lithium ion diffusion. However, cracking still occurs in those compounds and has been identified as one of the critical issues responsible for their capacity decay and short cycle life, although the diffusion-induced stress and volume expansion are much smaller than those in alloying-type electrodes. Here, we designed a thin-film model system that enables us to tailor the cation ordering in LiNi(0.5)Mn(1.5)O4 spinels and correlate the stress patterns, phase evolution, and cycle performances. Surprisingly, we found that distinct reaction paths cause negligible difference in the overall stress patterns but significantly different cracking behaviors and cycling performances: 95% capacity retention for disordered LiNi(0.5)Mn(1.5)O4 and 48% capacity retention for ordered LiNi(0.5)Mn(1.5)O4 after 2000 cycles. We were able to pinpoint that the extended solid-solution region with suppressed phase transformation attributed to the superior electrochemical performance of disordered spinel. This work envisions a strategy for rationally designing stable cathodes for lithium-ion batteries through engineering the atomic structure that extends the solid-solution region and suppresses phase transformation.

15.
Nano Lett ; 14(11): 6704-10, 2014 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-25314674

RESUMO

Silicon alloys have the highest specific capacity when used as anode material for lithium-ion batteries; however, the drastic volume change inherent in their use causes formidable challenges toward achieving stable cycling performance. Large quantities of binders and conductive additives are typically necessary to maintain good cell performance. In this report, only 2% (by weight) functional conductive polymer binder without any conductive additives was successfully used with a micron-size silicon monoxide (SiO) anode material, demonstrating stable and high gravimetric capacity (>1000 mAh/g) for ∼500 cycles and more than 90% capacity retention. Prelithiation of this anode using stabilized lithium metal powder (SLMP) improves the first cycle Coulombic efficiency of a SiO/NMC full cell from ∼48% to ∼90%. The combination enables good capacity retention of more than 80% after 100 cycles at C/3 in a lithium-ion full cell.

16.
ACS Appl Mater Interfaces ; 6(19): 17111-8, 2014 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-25203598

RESUMO

The mechanical failure at the electrode interfaces (laminate/current collector and binder/particle interfaces) leads to particle isolation and delamination, which has been regarded as one of the main reasons for the capacity decay and cell failure of lithium-ion batteries (LIBs). Polymer binder provides the key function for a good interface property and for maintaining the electrode integrity of LIBs. Triethylene glycol monomethyl ether (TEG) moieties were incorporated into polymethacrylic acid (PMAA) to different extents at the molecular level. Microscratch tests of the graphite electrodes based on these binders indicate that the electrode is more flexible with 5 or 10% TEG in the polymer binders. Crack generation is inhibited by the flexible TEG-containing binder, compared to that of the unmodified PMAA-based electrode, leading to the better cycling performance of the flexible electrode. With a 10% TEG moiety in the binder, the graphite half-cell reaches a reversible capacity of >270 mAh/g at the 1C rate, compared to a value of ∼190 mAh/g for the unmodified PMAA binder.

17.
ACS Appl Mater Interfaces ; 6(16): 13757-64, 2014 Aug 27.
Artigo em Inglês | MEDLINE | ID: mdl-25077883

RESUMO

A novel one-pot synthesis for the subeutectic growth of (111) oriented Si nanowires on an in situ formed nickel nanoparticle catalyst prepared from an inexpensive nickel nitrate precursor is developed. Additionally, anchoring the nickel nanoparticles to a simultaneously reduced graphene oxide support created synergy between the individual components of the c-SiNW-G composite, which greatly improved the reversible charge capacity and it is retention at high current density when applied as an anode for a Li-ion battery. The c-SiNW-G electrodes for Li-ion battery achieved excellent high-rate performance, producing a stable reversible capacity of 550 mAh g(-1) after 100 cycles at 6.8 A g(-1) (78% of that at 0.1 A g(-1)). Thus, with further development this process creates an important building block for a new wave of low-cost silicon nanowire materials and a promising avenue for high rate Li-ion batteries.

18.
Nano Lett ; 14(9): 5250-6, 2014 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-25158077

RESUMO

To better confine the sulfur/polysulfides in the electrode of lithium-sulfur (Li/S) batteries and improve the cycling stability, we developed a double-layered core-shell structure of polymer-coated carbon-sulfur. Carbon-sulfur was first prepared through the impregnation of sulfur into hollow carbon spheres under heat treatment, followed by a coating polymerization to give a double-layered core-shell structure. From the study of scanning transmission electron microscopy (STEM) images, we demonstrated that the sulfur not only successfully penetrated through the porous carbon shell but also aggregated along the inner wall of the carbon shell, which, for the first time, provided visible and convincing evidence that sulfur preferred diffusing into the hollow carbon rather than aggregating in/on the porous wall of the carbon. Taking advantage of this structure, a stable capacity of 900 mA h g(-1) at 0.2 C after 150 cycles and 630 mA h g(-1) at 0.6 C after 600 cycles could be obtained in Li/S batteries. We also demonstrated the feasibility of full cells using the sulfur electrodes to couple with the silicon film electrodes, which exhibited significantly improved cycling stability and efficiency. The remarkable electrochemical performance could be attributed to the desirable confinement of sulfur through the unique double-layered core-shell architectures.

19.
ACS Appl Mater Interfaces ; 6(10): 7292-300, 2014 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-24809928

RESUMO

Novel Mn(2+)-doped TiO2 nanosheet-based spheres have been successfully prepared via a simple hydrothermal and ion-exchange process. After hydrothermal growth, flowerlike nanosheet-based spheres of protonated dititanate were confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The hierarchical nanostructure was obtained via a dissolution-recrystallization process starting from a precursor of homogenous TiO2 nanospheres. Moreover, as-prepared protonated dititanate was converted to Mn-doped nanosheet-based spheres via the ion-exchange method. Then, both the doped and undoped protonated dititanate were calcined and tested as anode materials for lithium-ion battery applications at elevated temperatures. The undoped sample showed an initial capacity of 201 mAh g(-1) but only had 44.1% of the initial capacity retained after 50 cycles at mixed current densities of 30, 150, and 500 mA g(-1) at 55 °C, while the Mn-doped one exhibited an initial capacity of 190 mAh g(-1) and 91.4% capacity retention with superior reversible capacity under the same test conditions. Comparisons between different samples suggest that manganese ions on the surface of TiO2 nanosheet-based spheres are responsible for the enhanced electrochemical performance.

20.
Phys Chem Chem Phys ; 16(22): 10398-402, 2014 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-24733563

RESUMO

The structure, chemistry, and spatial distribution of Mn-bearing nanoparticles dissolved from the Li1.05Mn2O4 cathode during accelerated electrochemical cycling tests at 55 °C and deposited within the solid electrolyte interphase (SEI) are directly characterized through HRTEM imaging and XPS. Here we use air protection and vacuum transfer systems to transport cycled electrodes for imaging and analytical characterization. From HRTEM imaging, we find that a band of individual metallic Mn nanoparticles forms locally at the SEI/graphite interface while the internal and outermost layer of the SEI contains a mixture of LiF and MnF2 nanoparticles, which is confirmed with XPS. Based on our experimental findings we propose a new interpretation of how Mn is reduced from the cathode and how metallic Mn and Mn-bearing nanoparticles form within the SEI during electrochemical cycling.

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