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1.
Nat Commun ; 11(1): 606, 2020 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-32001696

RESUMO

Manipulating liquids with tunable shape and optical functionalities in real time is important for electroactive flow devices and optoelectronic devices, but remains a great challenge. Here, we demonstrate electrotunable liquid sulfur microdroplets in an electrochemical cell. We observe electrowetting and merging of sulfur droplets under different potentiostatic conditions, and successfully control these processes via selective design of sulfiphilic/sulfiphobic substrates. Moreover, we employ the electrowetting phenomena to create a microlens based on the liquid sulfur microdroplets and tune its characteristics in real time through changing the shape of the liquid microdroplets in a fast, repeatable, and controlled manner. These studies demonstrate a powerful in situ optical battery platform for unraveling the complex reaction mechanism of sulfur chemistries and for exploring the rich material properties of the liquid sulfur, which shed light on the applications of liquid sulfur droplets in devices such as microlenses, and potentially other electrotunable and optoelectronic devices.

2.
Nat Nanotechnol ; 2020 Jan 27.
Artigo em Inglês | MEDLINE | ID: mdl-31988508

RESUMO

It has recently been shown that sulfur, a solid material in its elementary form S8, can stay in a supercooled state as liquid sulfur in an electrochemical cell. We establish that this newly discovered state could have implications for lithium-sulfur batteries. Here, through in situ studies of electrochemical sulfur generation, we show that liquid (supercooled) and solid elementary sulfur possess very different areal capacities over the same charging period. To control the physical state of sulfur, we studied its growth on two-dimensional layered materials. We found that on the basal plane, only liquid sulfur accumulates; by contrast, at the edge sites, liquid sulfur accumulates if the thickness of the two-dimensional material is small, whereas solid sulfur nucleates if the thickness is large (tens of nanometres). Correlating the sulfur states with their respective areal capacities, as well as controlling the growth of sulfur on two-dimensional materials, could provide insights for the design of future lithium-sulfur batteries.

3.
Nat Commun ; 10(1): 5824, 2019 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-31862992

RESUMO

High coulombic efficiency and dendrite suppression in carbonate electrolytes remain challenges to the development of high-energy lithium ion batteries containing lithium metal anodes. Here we demonstrate an ultrathin (≤100 nm) lithium-ion ionomer membrane consisting of lithium-exchanged sulfonated polyether ether ketone embedded with polyhedral oligosilsesquioxane as a coating layer on copper or lithium for achieving efficient and stable lithium plating-stripping cycles in a carbonate-based electrolyte. Operando analyses and theoretical simulation reveal the remarkable ability of the ionomer coating to enable electric field homogenization over a considerably large lithium-plating surface. The membrane coating, serving as an artificial solid-electrolyte interphase filter in minimizing parasitic reactions at the electrolyte-electrode interface, enables dendrite-free lithium plating on copper with outstanding coulombic efficiencies at room and elevated (50 °C) temperatures. The membrane coated copper demonstrates itself as a promising current collector for manufacturing high-quality pre-plated lithium thin-film anode.

4.
ACS Cent Sci ; 5(4): 719-726, 2019 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-31041392

RESUMO

Heavy metal pollution continues to be one of the most serious environmental problems which has attracted major global concern. Here, a rapid, high-capacity, yet economical strategy for deep cleaning of heavy metals ions in water is reported based on amidoxime-functionalized macroporous carbon electrode materials. The active sites of our material can be self-refreshed during the electrochemical removal process, which is different from traditional methods. The novel filter device in this work can purify contaminated water very rapidly (3000 L h-1 m-2), and can decrease heavy metal ion concentrations to below 5 ppb with a very short contact time (only 3 s). The original treatment efficiency of the device can be retained even after 1 week of continuous device operation. An extremely high removal capacity of over 2300 mg g-1 can be achieved with 2-3 orders of magnitude higher efficiency than that of surface adsorption-based commercial filters without any decay. Additionally, the cost of energy consumed in our method is lower than $6.67 × 10-3 per ton of wastewater. We envision that this approach can be routinely applied for the rapid, efficient, and thorough removal of heavy metals from both point-of-use water and industrial wastewater.

5.
Nat Nanotechnol ; 14(7): 705-711, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31133663

RESUMO

The urgent need for safer batteries is leading research to all-solid-state lithium-based cells. To achieve energy density comparable to liquid electrolyte-based cells, ultrathin and lightweight solid electrolytes with high ionic conductivity are desired. However, solid electrolytes with comparable thicknesses to commercial polymer electrolyte separators (~10 µm) used in liquid electrolytes remain challenging to make because of the increased risk of short-circuiting the battery. Here, we report on a polymer-polymer solid-state electrolyte design, demonstrated with an 8.6-µm-thick nanoporous polyimide (PI) film filled with polyethylene oxide/lithium bis(trifluoromethanesulfonyl)imide (PEO/LiTFSI) that can be used as a safe solid polymer electrolyte. The PI film is nonflammable and mechanically strong, preventing batteries from short-circuiting even after more than 1,000 h of cycling, and the vertical channels enhance the ionic conductivity (2.3 × 10-4 S cm-1 at 30 °C) of the infused polymer electrolyte. All-solid-state lithium-ion batteries fabricated with PI/PEO/LiTFSI solid electrolyte show good cycling performance (200 cycles at C/2 rate) at 60 °C and withstand abuse tests such as bending, cutting and nail penetration.

6.
Nat Commun ; 10(1): 2067, 2019 05 06.
Artigo em Inglês | MEDLINE | ID: mdl-31061393

RESUMO

Fast-charging and high-energy-density batteries pose significant safety concerns due to high rates of heat generation. Understanding how localized high temperatures affect the battery is critical but remains challenging, mainly due to the difficulty of probing battery internal temperature with high spatial resolution. Here we introduce a method to induce and sense localized high temperature inside a lithium battery using micro-Raman spectroscopy. We discover that temperature hotspots can induce significant lithium metal growth as compared to the surrounding lower temperature area due to the locally enhanced surface exchange current density. More importantly, localized high temperature can be one of the factors to cause battery internal shorting, which further elevates the temperature and increases the risk of thermal runaway. This work provides important insights on the effects of heterogeneous temperatures within batteries and aids the development of safer batteries, thermal management schemes, and diagnostic tools.

7.
Sci Adv ; 5(3): eaau5655, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30899782

RESUMO

Lithium metal-based batteries are attractive energy storage devices because of high energy density. However, uncontrolled dendrite growth and virtually infinite volume change, which cause performance fading and safety concerns, have limited their applications. Here, we demonstrate that a composite lithium metal electrode with an ion-conducting mesoscale skeleton can improve electrochemical performance by locally reducing the current density. In addition, the potential for short-circuiting is largely alleviated due to side deposition of mossy lithium on the three-dimensional electroactive surface of the composite electrode. Moreover, the electrode volume only slightly changes with the support of a rigid and stable scaffold. Therefore, this mesoscale composite electrode can cycle stably for 200 cycles with low polarization under a high areal current density up to 5 mA/cm2. Most attractively, the proposed fabrication process, which only involves simple mechanical deformation, is scalable and cost effective, providing a new strategy for developing high performance and long lifespan lithium anodes.

8.
Nano Lett ; 19(2): 1326-1335, 2019 02 13.
Artigo em Inglês | MEDLINE | ID: mdl-30676759

RESUMO

Lithium (Li) metal has long been considered the "holy grail" of battery anode chemistry but is plagued by low efficiency and poor safety due to its high chemical reactivity and large volume fluctuation, respectively. Here we introduce a new host of wrinkled graphene cage (WGC) for Li metal. Different from recently reported amorphous carbon spheres, WGC show highly improved mechanical stability, better Li ion conductivity, and excellent solid electrolyte interphase (SEI) for continuous robust Li metal protection. At low areal capacities, Li metal is preferentially deposited inside the graphene cage. Cryogenic electron microscopy characterization shows that a uniform and stable SEI forms on the WGC surface that can shield the Li metal from direct exposure to electrolyte. With increased areal capacities, Li metal is plated densely and homogeneously into the outer pore spaces between graphene cages with no dendrite growth or volume change. As a result, a high Coulombic efficiency (CE) of ∼98.0% was achieved under 0.5 mA/cm2 and 1-10 mAh/cm2 in commercial carbonate electrolytes, and a CE of 99.1% was realized with high-concentration electrolytes under 0.5 mA/cm2 and 3 mAh/cm2. Full cells using WGC electrodes with prestored Li paired with Li iron phosphate showed greatly improved cycle lifetime. With 10 mAh/cm2 Li metal deposition, the WGC/Li composite anode was able to provide a high specific capacity of ∼2785 mAh/g. With its roll-to-roll compatible fabrication procedure, WGC serves as a highly promising material for the practical realization of Li metal anodes in next-generation high energy density secondary batteries.

9.
Nat Chem ; 11(4): 382-389, 2019 04.
Artigo em Inglês | MEDLINE | ID: mdl-30664717

RESUMO

Developing a viable metallic lithium anode is a prerequisite for next-generation batteries. However, the low redox potential of lithium metal renders it prone to corrosion, which must be thoroughly understood for it to be used in practical energy-storage devices. Here we report a previously overlooked mechanism by which lithium deposits can corrode on a copper surface. Voids are observed in the corroded deposits and a Kirkendall-type mechanism is validated through electrochemical analysis. Although it is a long-held view that lithium corrosion in electrolytes involves direct charge-transfer through the lithium-electrolyte interphase, the corrosion observed here is found to be governed by a galvanic process between lithium and the copper substrate-a pathway largely neglected by previous battery corrosion studies. The observations are further rationalized by detailed analyses of the solid-electrolyte interphase formed on copper and lithium, where the disparities in electrolyte reduction kinetics on the two surfaces can account for the fast galvanic process.

10.
ACS Nano ; 13(1): 737-744, 2019 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-30589528

RESUMO

Battery performance is critically dependent on the nanostructure and electrochemical properties of the solid-electrolyte interphase (SEI)-a passivation film that exists on most lithium-battery anodes. However, knowledge of how the SEI nanostructure forms and its impact on ionic transport remains limited due to its sensitivity to transmission electron microscopy and difficulty in accurately probing the SEI impedance. Here, we track the voltage-dependent, stepwise evolution of the nanostructure and impedance of the SEI on CuO nanowires using cryogenic-electron microscopy (cryo-EM) and electrochemical impedance spectroscopy (EIS). In carbonate electrolyte, the SEI forms at 1.0 V vs Li/Li+ as a 3 nm thick amorphous SEI and grows to 4 nm at 0.5 V; as the potential approaches 0.0 V vs Li/Li+, the SEI on the CuO nanowires forms an 8 nm thick inverted multilayered nanostructure in ethylene carbonate/diethyl carbonate (EC/DEC) electrolyte with 10 vol % fluoroethylene carbonate (FEC) and a mosaic nanostructure in EC/DEC electrolyte. Upon Li deposition, the total SEI thickness grows to 16 nm, and significant growth of the inner amorphous layer takes place in the inverted multilayered nanostructure, indicating that electrolyte permeates the SEI. Using a refined EIS methodology, we isolate the SEI impedance on Cu and find that the SEI nanostructure directly correlates to macroscopic Li-ion transport through the SEI. The inverted layered nanostructure decreases the interfacial impedance upon formation, whereas the mosaic nanostructure continually increases the interfacial impedance during growth. These structural and electrochemical findings illustrate a more complete portrait of SEI formation and guide further improvements in engineered SEI.

11.
Nano Lett ; 18(11): 7060-7065, 2018 11 14.
Artigo em Inglês | MEDLINE | ID: mdl-30339401

RESUMO

The nanostructure design of a prereserved hollow space to accommodate 300% volume change of silicon anodes has created exciting promises for high-energy batteries. However, challenges with weak mechanical stability during the calendering process of electrode fabrication and poor volumetric energy density remain to be solved. Here we fabricated a pressure-resistant silicon structure by designing a dense silicon shell coating on secondary micrometer particles, each consisting of many silicon nanoparticles. The silicon skin layer significantly improves mechanical stability, while the inner porous structure efficiently accommodates the volume expansion. Such a structure can resist a high pressure of over 100 MPa and is well-maintained after the calendering process, demonstrating a high volumetric capacity of 2041 mAh cm-3. In addition, the dense silicon shell decreases the surface area and thus increases the initial Coulombic efficiency. With further encapsulation with a graphene cage, which allows the silicon core to expand within the cage while retaining electrical contact, the silicon hollow structure exhibits a high initial Coulombic efficiency and fast rise of later Coulombic efficiencies to >99.5% and superior stability in a full-cell battery.

12.
Nat Commun ; 9(1): 3656, 2018 09 07.
Artigo em Inglês | MEDLINE | ID: mdl-30194431

RESUMO

The physiochemical properties of the solid-electrolyte interphase, primarily governed by electrolyte composition, have a profound impact on the electrochemical cycling of metallic lithium. Herein, we discover that the effect of nitrate anions on regulating lithium deposition previously known in ether-based electrolytes can be extended to carbonate-based systems, which dramatically alters the nuclei from dendritic to spherical, albeit extremely limited solubility. This is attributed to the preferential reduction of nitrate during solid-electrolyte interphase formation, and the mechanisms behind which are investigated based on the structure, ion-transport properties, and charge transfer kinetics of the modified interfacial environment. To overcome the solubility barrier, a solubility-mediated sustained-release methodology is introduced, in which nitrate nanoparticles are encapsulated in porous polymer gel and can be steadily dissolved during battery operation to maintain a high concentration at the electroplating front. As such, effective dendrite suppression and remarkably enhanced cycling stability are achieved in corrosive carbonate electrolytes.

13.
Sci Adv ; 4(7): eaat5168, 2018 07.
Artigo em Inglês | MEDLINE | ID: mdl-30062125

RESUMO

Lithium metal has long been considered one of the most promising anode materials for advanced lithium batteries (for example, Li-S and Li-O2), which could offer significantly improved energy density compared to state-of-the-art lithium ion batteries. Despite decades of intense research efforts, its commercialization remains limited by poor cyclability and safety concerns of lithium metal anodes. One root cause is the parasitic reaction between metallic lithium and the organic liquid electrolyte, resulting in continuous formation of an unstable solid electrolyte interphase, which consumes both active lithium and electrolyte. Until now, it has been challenging to completely shut down the parasitic reaction. We find that a thin-layer coating applied through atomic layer deposition on a hollow carbon host guides lithium deposition inside the hollow carbon sphere and simultaneously prevents electrolyte infiltration by sealing pinholes on the shell of the hollow carbon sphere. By encapsulating lithium inside the stable host, parasitic reactions are prevented, resulting in impressive cycling behavior. We report more than 500 cycles at a high coulombic efficiency of 99% in an ether-based electrolyte at a cycling rate of 0.5 mA/cm2 and a cycling capacity of 1 mAh/cm2, which is among the most stable Li anodes reported so far.

14.
J Am Chem Soc ; 140(37): 11735-11744, 2018 09 19.
Artigo em Inglês | MEDLINE | ID: mdl-30152228

RESUMO

The electrodeposition of lithium metal is a key process in next-generation, high energy density storage devices. However, the high reactivity of the lithium metal causes short cycling lifetimes and dendrite growth that can pose a serious safety issue. Recently, a number of approaches have been pursued to stabilize the lithium metal-electrolyte interface, including soft polymeric coatings that have shown the ability to enable high-rate and high-capacity lithium metal cycling, but a clear understanding of how to design and modify these coatings has not yet been established. In this work, we studied the effects of several polymers with systematically varied chemical and mechanical properties as coatings on the lithium metal anode. By examining the early stages of lithium metal deposition, we determine that the morphology of the lithium particles is strongly influenced by the chemistry of the polymer coating. We have identified polymer dielectric constant and surface energy as two key descriptors of the lithium deposit size. Low surface energy polymers were found to promote larger deposits with smaller surface areas. This may be explained by a reduced interaction between the coating and the lithium surface and thus an increase in the interfacial energy. On the other hand, high dielectric constant polymers were found to increase the exchange current and gave larger lithium deposits due to the decreased overpotentials at a fixed current density. We also observed that the thickness of the polymer coating should be optimized for each individual polymer. Furthermore, polymer reactivity was found to strongly influence the Coulombic efficiency. Overall, this work offers new fundamental insights into lithium electrodeposition processes and provides direction for the design of new polymer coatings to better stabilize the lithium metal anode.

15.
Proc Natl Acad Sci U S A ; 115(34): 8529-8534, 2018 08 21.
Artigo em Inglês | MEDLINE | ID: mdl-30082382

RESUMO

Lithium stripping is a crucial process coupled with lithium deposition during the cycling of Li metal batteries. Lithium deposition has been widely studied, whereas stripping as a subsurface process has rarely been investigated. Here we reveal the fundamental mechanism of stripping on lithium by visualizing the interface between stripped lithium and the solid electrolyte interphase (SEI). We observed nanovoids formed between lithium and the SEI layer after stripping, which are attributed to the accumulation of lithium metal vacancies. High-rate dissolution of lithium causes vigorous growth and subsequent aggregation of voids, followed by the collapse of the SEI layer, i.e., pitting. We systematically measured the lithium polarization behavior during stripping and find that the lithium cation diffusion through the SEI layer is the rate-determining step. Nonuniform sites on typical lithium surfaces, such as grain boundaries and slip lines, greatly accelerated the local dissolution of lithium. The deeper understanding of this buried interface stripping process provides beneficial clues for future lithium anode and electrolyte design.

16.
Sci Adv ; 4(6): eaas9820, 2018 06.
Artigo em Inglês | MEDLINE | ID: mdl-29942858

RESUMO

Lithium-ion batteries (LIBs) are considered to be one of the most important energy storage technologies. As the energy density of batteries increases, battery safety becomes even more critical if the energy is released unintentionally. Accidents related to fires and explosions of LIBs occur frequently worldwide. Some have caused serious threats to human life and health and have led to numerous product recalls by manufacturers. These incidents are reminders that safety is a prerequisite for batteries, and serious issues need to be resolved before the future application of high-energy battery systems. This Review aims to summarize the fundamentals of the origins of LIB safety issues and highlight recent key progress in materials design to improve LIB safety. We anticipate that this Review will inspire further improvement in battery safety, especially for emerging LIBs with high-energy density.

17.
Nano Lett ; 18(6): 3829-3838, 2018 06 13.
Artigo em Inglês | MEDLINE | ID: mdl-29727578

RESUMO

Among all solid electrolytes, composite solid polymer electrolytes, comprised of polymer matrix and ceramic fillers, garner great interest due to the enhancement of ionic conductivity and mechanical properties derived from ceramic-polymer interactions. Here, we report a composite electrolyte with densely packed, vertically aligned, and continuous nanoscale ceramic-polymer interfaces, using surface-modified anodized aluminum oxide as the ceramic scaffold and poly(ethylene oxide) as the polymer matrix. The fast Li+ transport along the ceramic-polymer interfaces was proven experimentally for the first time, and an interfacial ionic conductivity higher than 10-3 S/cm at 0 °C was predicted. The presented composite solid electrolyte achieved an ionic conductivity as high as 5.82 × 10-4 S/cm at the electrode level. The vertically aligned interfacial structure in the composite electrolytes enables the viable application of the composite solid electrolyte with superior ionic conductivity and high hardness, allowing Li-Li cells to be cycled at a small polarization without Li dendrite penetration.

18.
ACS Cent Sci ; 4(1): 97-104, 2018 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-29392181

RESUMO

Lithium metal is the ultimate anode choice for high energy density rechargeable lithium batteries. However, it suffers from inferior electrochemical performance and safety issues due to its high reactivity and the growth of lithium dendrites. It has long been desired to develop a materials coating on Li metal, which is pinhole-free, mechanically robust without fracture during Li metal deposition and stripping, and chemically stable against Li metal and liquid electrolytes, all while maintaining adequate ionic conductivity. However, such an ideal material coating has yet to be found. Here we report a novel synthesis method by reacting clean molten lithium foil directly with pure nitrogen gas to generate instantaneously a pinhole-free and ionically conductive α-Li3N film directly bonded onto Li metal foil. The film consists of highly textured large Li3N grains (tens of µm) with (001) crystalline planes parallel to the Li metal surface. The bonding between textured grains is strong, resulting in a mechanically robust film which does not crack even when bent to a 0.8 cm curvature radius and is found to maintain pinhole-free coverage during Li metal deposition and stripping. The measured ionic conductivity is up to 5.2 × 10-4 S cm-1, sufficient for maintaining regular current densities for controllable film thicknesses ranging from 2 to 30 µm. This Li3N coating is chemically stable, isolating the reactive metallic lithium from liquid electrolyte, prevents continuous electrolyte consumption during battery cycling, and promotes dendrite-free uniform lithium plating/stripping underneath. We demonstrated Li|Li4Ti5O12 cells with stable and flat potential profiles for 500 cycles without capacity decay or an increase in potential hysteresis.

19.
Nano Lett ; 18(2): 1130-1138, 2018 02 14.
Artigo em Inglês | MEDLINE | ID: mdl-29297691

RESUMO

Aerosol-induced haze problem has become a serious environmental concern. Filtration is widely applied to remove aerosols from gas streams. Despite classical filtration theories, the nanoscale capture and evolution of aerosols is not yet clearly understood. Here we report an in situ investigation on the nanoscale capture and evolution of aerosols on polyimide nanofibers. We discovered different capture and evolution behaviors among three types of aerosols: wetting liquid droplets, nonwetting liquid droplets, and solid particles. The wetting droplets had small contact angles and could move, coalesce, and form axisymmetric conformations on polyimide nanofibers. In contrast, the nonwetting droplets had a large contact angle on polyimide nanofibers and formed nonaxisymmetric conformations. Different from the liquid droplets, the solid particles could not move along the nanofibers and formed dendritic structures. This study provides an important insight for obtaining a deep understanding of the nanoscale capture and evolution of aerosols and benefits future design and development of advanced filters.

20.
Sci Adv ; 3(11): eaao3170, 2017 11.
Artigo em Inglês | MEDLINE | ID: mdl-29202031

RESUMO

Defects are important features in two-dimensional (2D) materials that have a strong influence on their chemical and physical properties. Through the enhanced chemical reactivity at defect sites (point defects, line defects, etc.), one can selectively functionalize 2D materials via chemical reactions and thereby tune their physical properties. We demonstrate the selective atomic layer deposition of LiF on defect sites of h-BN prepared by chemical vapor deposition. The LiF deposits primarily on the line and point defects of h-BN, thereby creating seams that hold the h-BN crystallites together. The chemically and mechanically stable hybrid LiF/h-BN film successfully suppresses lithium dendrite formation during both the initial electrochemical deposition onto a copper foil and the subsequent cycling. The protected lithium electrodes exhibit good cycling behavior with more than 300 cycles at relatively high coulombic efficiency (>95%) in an additive-free carbonate electrolyte.

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