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1.
    
Alloying anodes such as silicon are promising electrode materials for next‐generation high energy density lithium‐ion batteries because of their ability to reversibly incorporate a high concentration of Li atoms. However, alloying anodes usually exhibit a short cycle life due to the extreme volumetric and structural changes that occur during lithium insertion/extraction; these transformations cause mechanical fracture and exacerbate side reactions. To solve these problems, there has recently been significant attention devoted to creating silicon nanostructures that can accommodate the lithiation‐induced strain and thus exhibit high Coulombic efficiency and long cycle life. In parallel, many experiments and simulations have been conducted in an effort to understand the details of volumetric expansion, fracture, mechanical stress evolution, and structural changes in silicon nanostructures. The fundamental materials knowledge gained from these studies has provided guidance for designing optimized Si electrode structures and has also shed light on the factors that control large‐volume change solid‐state reactions. In this paper, we review various fundamental studies that have been conducted to understand structural and volumetric changes, stress evolution, mechanical properties, and fracture behavior of nanostructured Si anodes for lithium‐ion batteries and compare the reaction process of Si to other novel anode materials.  相似文献   

2.
    
The development of sodium‐ion batteries has drawn lots of attention recently due to the low‐cost and eco‐friendly sodium source. However, a fundamental understanding of the sodiation behavior for commonly used electrode materials is still limited. Here, combining in situ transmission electron microscopy, aberration‐corrected scanning transmission electron microscopy, and ex situ battery cycling tests, the lithiation and sodiation behavior of ZnO nanowires is investigated. The findings show a direct correlation between the mechanical behavior of the lithiated/sodiated ZnO nanowires and their electrochemical cyclability. The mechanical brittleness of LiZn and the formation of nanocracks lead to the poor cyclability of Li‐ion batteries with a ZnO anode. However, the sodiated ZnO nanowires show profuse dislocation plasticity. The observed high‐density dislocations offer the sodiated ZnO anode more ductility and subsequently better cyclability than its Li‐ion counterpart. The results reveal the importance of understanding the correlation between mechanical properties of battery electrodes and their cycling abilities.  相似文献   

3.
    
Developing high‐voltage cathode materials is critical for sodium‐ion batteries to boost energy density. NASICON (Na super‐ionic conductor)‐structured NaxMnM(PO4)3 materials (M represents transition metal) have drawn increasing attention due to their features of robust crystal framework, low cost, as well as high voltage based on Mn4+/Mn3+ and Mn3+/Mn2+ redox couples. However, full activation of Mn4+/Mn3+ redox couple within NASICON framework is still a great challenge. Herein, a novel NASICON‐type Na4MnCr(PO4)3 material with highly reversible Mn4+/Mn3+ redox reaction is discovered. It proceeds a two‐step reaction with voltage platforms centered at 4.15 and 3.52 V versus Na+/Na, delivering a capacity of 108.4 mA h g?1. The Na4MnCr(PO4)3 cathode also exhibits long durability over 500 cycles and impressive rate capability up to 10 C. The galvanostatic intermittent titration technique (GITT) test shows fast Na diffusivity which is further verified by density functional theory calculations. The high electrochemical activity derives from the 3D robust framework structure, fast kinetics, and pseudocapacitive contribution. The sodium storage mechanism of the Na4MnCr(PO4)3 cathode is deeply studied by ex situ X‐ray diffraction (XRD) and ex situ X‐ray photoelectron spectroscopy (XPS), revealing that both solid‐solution and two‐phase reactions are involved in the Na+ ions extraction/insertion process.  相似文献   

4.
    
Understanding and possibly recovering from the failure mechanisms of phase change memories (PCMs) are critical to improving their cycle life. Extensive electrical testing and postfailure electron microscopy analysis have shown that stuck–set failure can be recovered. Here, self‐healing of novel confined PCM devices is directly shown by controlling the electromigration of the phase change material at the nanoscale. In contrast to the current mushroom PCM, the confined PCM has a metallic surfactant layer, which enables effective Joule heating to control the phase change material even in the presence of a large void. In situ transmission electron microscope movies show that the voltage polarity controls the direction of electromigration of the phase change material, which can be used to fill nanoscale voids that form during programing. Surprisingly, a single voltage pulse can induce dramatic migration of antimony (Sb) due to high current density in the PCM device. Based on the finding, self‐healing of a large void inside a confined PCM device with a metallic liner is demonstrated for the first time.  相似文献   

5.
    
Understanding the structural evolution of Li2S upon operation of lithium‐sulfur (Li‐S) batteries is inadequate and a complete decomposition of Li2S during charge is difficult. Whether it is the low electronic conductivity or the low ionic conductivity of Li2S that inhibits its decomposition is under debate. Furthermore, the decomposition pathway of Li2S is also unclear. Herein, an in situ transmission electron microscopy (TEM) technique implemented with a microelectromechanical systems (MEMS) heating device is used to study the precipitation and decomposition of Li2S at high temperatures. It is revealed that Li2S transformed from an amorphous/nanocrystalline to polycrystalline state with proceeding of the electrochemical lithiation at room temperature (RT), and the precipitation of Li2S is more complete at elevated temperatures than at RT. Moreover, the decomposition of Li2S that is difficult to achieve at RT becomes facile with increased Li+ ion conduction at high temperatures. These results indicate that Li+ ion diffusion in Li2S dominates its reversibility in the solid‐state Li‐S batteries. This work not only demonstrates the powerful capabilities of combining in situ TEM with a MEMS heating device to explore the basic science in energy storage materials at high temperatures but also introduces the factor of temperature to boost battery performance.  相似文献   

6.
    
Phase transition is a fundamental physical phenomenon that has been widely studied both theoretically and experimentally. According to the Landau theory, the coexistence of high‐ and low‐temperature phases is thermodynamically impossible during a second‐order phase transition in a bulk single crystal. Here, the coexistence of two (α and β) phases in wedge‐shaped nanosized single‐crystal Cu2Se over a large temperature range are demonstrated. By considering the surface free‐energy difference between the two phases and the shape effect, a thermodynamic model is established, which explicitly explains their coexistence. Intriguingly, it is found that with a precise control of the heating temperature, the phase boundary can be manipulated at atomic level. These discoveries extend the understanding of phase transitions to the nanoscale and shed light on rational manipulation of phase transitions in nanomaterials.  相似文献   

7.
    
PtPb@Pt catalysts are very useful and widely applied in various industrial reactions. Here, the phase stability of such catalysts is compared in both CO gas and vacuum conditions at elevated temperatures using aberration‐corrected in situ transmission electron microscopy (TEM). A Pt aggregation process takes place affected by CO gas, which results in direct exposure of the PtPb core to CO. A phase separation process, in which Pb atoms are stripped off the original PtPb@Pt nanoparticles, is unambiguously identified in CO gas. At initial stages, the as nucleated Pb islands are amorphous. Once the ultrathin Pb islands reach ≈3.5 nm or higher, they suddenly became crystalline. The interaction between Pb and CO gas stabilizes the ultrathin Pb nanosheets, resulting in the formation of a large quantity of Pb nanosheets and Pb‐depleted PtPb0.08 nanoparticles. In sharp contrast, when heated up in a vacuum, the PtPb@Pt catalyst remains intact. The results of this study shine light on the “toxic” effect of CO that results in failures of many Pt‐based catalysts and discloses formation mechanism of ultrathin Pb nanosheets.  相似文献   

8.
    
In order to meet the growing demands of electric vehicles and portable devices, the electrochemical performance of rechargeable batteries is required to be further optimized. Above all, it is of vital importance to understand the reaction mechanism of batteries under working states, which requires a direct observation of the complicated reaction process. Thus, in situ X‐ray diffraction (XRD) techniques have been employed in the charge and discharge process to realize real‐time monitoring and provide on‐site information of structural evolutions and phase transitions within electrode materials. In this review, a detailed summary of lab‐scale in situ X‐ray diffraction techniques is given and compared with in situ synchrotron XRD at the same time. First, four typical in situ reaction mechanisms are presented and their distinctive characteristics are introduced in detail. Second, the practical applications of in situ X‐ray diffraction in different battery systems are described with examples after extensive collections. In addition, the design of in situ cells and some noteworthy experimental details in actual testing are also mentioned. Finally, the further development direction of in situ X‐ray diffraction techniques is well prospected.  相似文献   

9.
    
As an important aspect of crystal phase engineering, controlled crystal phase transformation of noble metal nanomaterials has emerged as an effective strategy to explore novel crystal phases of nanomaterials. In particular, it is of significant importance to observe the transformation pathway and reveal the transformation mechanism in situ. Here, the phase transformation behavior of face‐centered cubic (fcc) Au nanoparticles (fcc‐AuNPs), adhering to the surface of 4H nanodomains in 4H/fcc Au nanorods, referred to as 4H‐AuNDs, during in situ transmission electron microscopy imaging is systematically studied. It is found that the phase transformation is dependent on the ratio of the size of the monocrystalline nanoparticle (NP) to the diameter of 4H‐AuND. Furthermore, molecular dynamics simulation and theoretical modeling are used to explain the experimental results, giving a size‐dependent phase transformation diagram which provides a general guidance to predict the phase transformation pathway between fcc and 4H Au nanomaterials. Impressively, this method is general, which is used to study the phase transformation of other metal NPs, such as Pd, Ag, and PtPdAg, adhering to 4H‐AuNDs. The work opens an avenue for selective phase engineering of nanomaterials which may possess unique physicochemical properties and promising applications.  相似文献   

10.
    
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11.
    
The formation of low resistance and self‐aligned contacts with thermally stable alloyed phases is a prerequisite for realizing reliable functionality in ultrascaled semiconductor transistors. Detailed structural analysis of the phase transformation accompanying contact alloying can facilitate contact engineering as transistor channels approach a few atoms across. Original in situ heating transmission electron microscopy studies are carried out to record and analyze the atomic scale dynamics of contact alloy formation between Ni and In0.53Ga0.47As nanowire channels. It is observed that the nickelide reacts on the In0.53Ga0.47As (111) || Ni2In0.53Ga0.47As (0001) interface with atomic ledge propagation along the Ni2In0.53Ga0.47As direction. Ledges nucleate as a train of strained single‐bilayers and propagate in‐plane as double‐bilayers that are associated with a misfit dislocation of . The atomic structure is reconstructed to explain this phase transformation that involves collective gliding of three Shockley partials in In0.53Ga0.47As lattice to cancel out shear stress and the formation of misfit dislocations to compensate the large lattice mismatch in the newly formed nickelide phase and the In0.53Ga0.47As layers. This work demonstrates the applicability of interfacial disconnection (ledge + dislocation) theory in a nanowire channel during thermally induced phase transformation that is typical in metal/III–V semiconductor reactions.  相似文献   

12.
    
To develop strategies for efficient photo‐electrochemical water‐splitting, it is important to understand the fundamental properties of oxide photoelectrodes by synthesizing and investigating their single‐crystal thin films. However, it is challenging to synthesize high‐quality single‐crystal thin films from copper‐based oxide photoelectrodes due to the occurrence of significant defects such as copper or oxygen vacancies and grains. Here, the CuBi2O4 (CBO) single‐crystal thin film photocathode is achieved using a NiO template layer grown on single‐crystal SrTiO3 (STO) (001) substrate via pulsed laser deposition. The NiO template layer plays a role as a buffer layer of large lattice mismatch between CBO and STO (001) substrate through domain‐matching epitaxy, and forms a type‐II band alignment with CBO, which prohibits the transfer of photogenerated electrons toward bottom electrode. The photocurrent densities of the CBO single‐crystal thin film photocathode demonstrate ?0.4 and ?0.7 mA cm?2 at even 0 VRHE with no severe dark current under illumination in a 0.1 m potassium phosphate buffer solution without and with H2O2 as an electron scavenger, respectively. The successful synthesis of high‐quality CBO single‐crystal thin film would be a cornerstone for the in‐depth understanding of the fundamental properties of CBO toward efficient photo‐electrochemical water‐splitting.  相似文献   

13.
    
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14.
    
Lithium–ion batteries (LIBs) has been developed over the last three decades. Increased amount of silicon (Si) is added into graphite anode to increase the energy density of LIBs. However, the amount of Si is limited, due to its structural instability and poor electronic conductivity so a novel approach is needed to overcome these issues. In this work, the synthesized chromium silicide (CrSi2) doped Si nanoparticle anode material achieves an initial capacity of 1729.3 mAh g−1 at 0.2C and retains 1085 mAh g−1 after 500 cycles. The new anode also shows fast charge capability due to the enhanced electronic conductivity provided by CrSi2 dopant, delivering a capacity of 815.9 mAh g−1 at 1C after 1000 cycles with a capacity degradation rate of <0.05% per cycle. An in situ transmission electron microscopy is used to study the structural stability of the CrSi2-doped Si, indicating that the high control of CrSi2 dopant prevents the fracture of Si during lithiation and results in long cycle life. Molecular dynamics simulation shows that CrSi2 doping optimizes the crack propagation path and dissipates the fracture energy. In this work a comprehensive information is provided to study the function of metal ion doping in electrode materials.  相似文献   

15.
    
The emergence of one‐dimensional nanostructures as fundamental constituents of advanced materials and next‐generation electronic and electromechanical devices has increased the need for their atomic‐scale characterization. Given its spatial and temporal resolution, coupled with analytical capabilities, transmission electron microscopy (TEM) has been the technique of choice in performing atomic structure and defect characterization. A number of approaches have been recently developed to combine these capabilities with in‐situ mechanical deformation and electrical characterization in the emerging field of in‐situ TEM electromechanical testing. This has enabled researchers to establish unambiguous synthesis‐structure‐property relations for one‐dimensional nanostructures. In this article, the development and latest advances of several in‐situ TEM techniques to carry out mechanical and electromechanical testing of nanowires and nanotubes are reviewed. Through discussion of specific examples, it is shown how the merging of several microsystems and TEM has led to significant insights into the behavior of nanowires and nanotubes, underscoring the significant role in‐situ techniques play in the development of novel nanoscale systems and materials.  相似文献   

16.
    
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17.
    
In this work, the authors explore the sodium salt of the 14‐vanado(V)phosphate, Na7[H2PV14O42], as a potential anode material for sodium‐ion batteries (NIBs). The multi‐electron redox activity of the polyoxovanadate [H2PV14O42]7‐leads to high capacity. This polyanion is synthesized by a simple aqueous solution procedure and isolate as a sodium salt with different numbers of crystal waters, Na7[H2PV14O42]·nH2O (n = 15–24). Na7[H2PV14O42] as anode in NIBs exhibits a high and reversible capacity of 322 mA h g−1 at 25 mA g−1 with a high cycling stability (with capacity retention of 87% after 120 cycles). Some of the V5+ ions in [H2PV14O42]7‐ can be reduced to V3+ after being discharged to 0.01 V versus Na/Na+, resulting in an average oxidation state of V3.7+, as based on ex situ X‐ray photoelectron spectroscopy and in situ synchrotron X‐ray absorption near edge structure studies. The crystalline material becomes amorphous during the charge/discharge processes, which can be observed by in situ synchrotron X‐ray diffraction, indicating that functionality does not require crystallinity. The authors propose that the charge storage mechanism of Na7[H2PV14O42] anodes mainly involves redox reactions of V accompanied by insertion/extraction of Na ions in‐between polyoxo‐14‐vanadate ions and adsorption/desorption of Na ions on the surface of the vanadate material.  相似文献   

18.
    
The control and rational design of redox‐based memristive devices, which are highly attractive candidates for next‐generation nonvolatile memory and logic applications, is complicated by competing and poorly understood switching mechanisms, which can result in two coexisting resistance hystereses that have opposite voltage polarity. These competing processes can be defined as regular and anomalous resistive switching. Despite significant characterization efforts, the complex nanoscale redox processes that drive anomalous resistive switching and their implications for current transport remain poorly understood. Here, lateral and vertical mapping of O vacancy concentrations is used during the operation of such devices in situ in an aberration corrected transmission electron microscope to explain the anomalous switching mechanism. It is found that an increase (decrease) in the overall O vacancy concentration within the device after positive (negative) biasing of the Schottky‐type electrode is associated with the electrocatalytic release and reincorporation of oxygen at the electrode/oxide interface and is responsible for the resistance change. This fundamental insight presents a novel perspective on resistive switching processes and opens up new technological opportunities for the implementation of memristive devices, as anomalous switching can now be suppressed selectively or used deliberately to achieve the desirable so‐called deep Reset.  相似文献   

19.
    
Bulk gold's attributes of relative chemical inertness, rarity, relatively low melting point and its beautiful sheen make it a prized material for humans. Recordings suggest it was the first metal employed by humans dating as far back to the late Paleolithic period ≈40 000 BC. However, at the nanoscale gold is expected to present new and exciting properties, not least in catalysis. Moreover, recent studies suggest a new family of single‐atom‐thick two‐dimensional (2D) metals exist. This work shows single‐atom‐thick freestanding gold membranes and nanoribbons can form as suspended structures in graphene pores. Electron irradiation is shown to lead to changes to the graphene pores which lead to dynamic changes of the gold membranes which transition to a nanoribbon. The freestanding single‐atom‐thick 2D gold structures are relatively stable to electron irradiation for extended periods. The work should advance the development of 2D gold monolayers significantly.  相似文献   

20.
    
The electrochemical performance of most transition metal oxides based on the conversion mechanism is greatly restricted by inferior cycling stability, rate capability, high overpotential induced by the serious irreversible reactions, low electrical conductivity, and poor ion diffusivity. To mitigate these problems, highly porous Mn3O4 micro/nanocuboids with in situ formed carbon matrix (denoted as Mn3O4@C micro/nanocuboids) are designed and synthesized via a one‐pot hydrothermal method, in which glucose plays the roles of a reductive agent and a carbon source simultaneously. The carbon content, particle size, and pore structure in the composite can be facilely controlled, resulting in continuous carbon matrix with abundant pores in the cuboids. The as‐fabricated Mn3O4@C micro/nanocuboids exhibit large reversible specific capacity (879 mAh g?1 at the current density of 100 mA g?1) as well as outstanding cycling stability (86% capacity retention after 500 cycles) and rate capability, making it a potential candidate as anode material for lithium‐ion batteries. Moreover, this facile and effective synthetic strategy can be further explored as a universal approach for the synthesis of other hierarchical transition metal oxides and carbon hybrids with subtle structure engineering.  相似文献   

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