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1.
    
2D vanadium carbide MXene containing surface functional groups (denoted as V2CTx , where Tx are surface functional groups) is synthesized and studied as anode material for Na‐ion batteries. V2CTx anode exhibits reversible charge storage with good cycling stability and high rate capability through electrochemical test. The charge storage mechanism of V2CTx material during Na+ intercalation/deintercalation and the redox reaction of vanadium are studied using a combination of synchrotron based X‐ray diffraction, hard X‐ray absorption near edge spectroscopy (XANES), and soft X‐ray absorption spectroscopy (sXAS). Experimental evidence of a major contribution of redox reaction of vanadium to the charge storage and the reversible capacity of V2CTx during sodiation/desodiation process are provided through V K ‐edge XANES and V L 2,3‐edge sXAS results. A correlation between the CO32? content and the Na+ intercalation/deintercalation states in the V2CTx electrode observed from C and O K ‐edge in sXAS results implies that some additional charge storage reactions may take place between the Na+‐intercalated V2CTx and the carbonate‐based nonaqueous electrolyte. The results of this study provide valuable information for the further studies on V2CTx as anode material for Na‐ion batteries and capacitors.  相似文献   

2.
    
Sodium‐ion batteries may become an alternative to the widespread lithium‐ion technology due to cost and kinetic advantages provided that cyclability is improved. For this purpose, the interplay between electrochemical and structural processes is key and is demonstrated in this work for Na2.46V6O16 (NVO) and Li2.55V6O16 employing operando synchrotron X‐ray diffraction. When NVO is cycled between 4.0 and 1.6 V, Na‐ions reversibly occupy two crystallographic sites, which results in remarkable cyclability. Upon discharge to 1.0 V, however, Na‐ions occupy also interstitial sites, inducing irreversible structural change with some loss of crystallinity concomitant with a decrease in capacity. Capacity fading increases with the ionic radius of the alkali ions (K+ > Na+ > Li+), suggesting that smaller ions stabilize the structure. This correlation of structural variation and electrochemical performance suggests a route toward improving cycling stability of a sodium‐ion battery. Its essence is a minor Li+‐retention in the A2+xV6O16 structure. Even though the majority of Li‐ions are replaced by the abundant Na+, the residual Li‐ions (≈10%) are sufficient to stabilize the layered structure, diminishing the irreversible structural damage. These results pave the way for further exploitation of the role of small ions in lattice stabilization that increases cycling performance.  相似文献   

3.
    
A microfluidic platform was used to address the problems of obtaining diffraction‐quality crystals and crystal handling during transfer to the X‐ray diffractometer. Crystallization conditions of a protein of pharmaceutical interest were optimized and X‐ray data were collected both in situ and ex situ .  相似文献   

4.
    
Operando X‐ray diffraction (XRD) and X‐ray absorption spectroscopy (XAS) studies of Ge anodes are carried out to understand the effect of cycling rate on Ge phase transformation during charge/discharge process and to relate that effect to capacity. It is discovered that the formation of crystalline Li15Ge4 (c‐Li15Ge4) during lithiation is suppressed beyond a certain cycling rate. A very stable and reversible high capacity of ≈1800 mAh g?1 can be attained up to 100 cycles at a slow C‐rate of C/21 when there is complete conversion of Ge anode into c‐Li15Ge4. When the C‐rate is increased to ≈C/10, the lithiation reaction is more heterogeneous and a relatively high capacity of ≈1000 mAh g?1 is achieved with poorer electrochemical reversibility. An increase in C‐rate to C/5 and higher reduces the capacity (≈500 mAh g?1) due to an impeded transformation from amorphous LixGe to c‐Li15Ge4, and yet improves the electrochemical reversibility. A proposed mechanism is presented to explain the C‐rate dependent phase transformations and the relationship of these to capacity fading. The operando XRD and XAS results provide new insights into the relationship between structural changes in Ge and battery capacity, which are important for guiding better design of high‐capacity anodes.  相似文献   

5.
    
Layered lithium nickel oxide (LiNiO2) can provide very high energy density among intercalation cathode materials for lithium‐ion batteries, but suffers from poor cycle life and thermal‐abuse tolerance with large lithium utilization. In addition to stabilization of the active cathode material, a concurrent development of electrolyte systems of better compatibility is critical to overcome these limitations for practical applications. Here, with nonaqueous electrolytes based on exclusively aprotic acyclic carbonates free of ethylene carbonate (EC), superior electrochemical and thermal characteristics are obtained with an ultrahigh‐nickel cathode (LiNi0.94Co0.06O2), capable of reaching a 235 mA h g?1 specific capacity. Pouch‐type graphite|LiNi0.94Co0.06O2 cells in EC‐free electrolytes withstand several hundred charge–discharge cycles with minor degradation at both ambient and elevated temperatures. In thermal‐abuse tests, the cathode at full charge, while reacting aggressively with EC‐based electrolytes below 200 °C, shows suppressed self‐heating without EC. Through 3D chemical and structural analyses, the intriguing impact of EC is visualized in aggravating unwanted surface parasitic reactions and irreversible bulk structural degradation of the cathode at high voltages. These results provide important insights in designing high‐energy electrodes for long‐lasting and reliable lithium‐ion batteries.  相似文献   

6.
    
Silicon‐based anodes are an appealing alternative to graphite for lithium‐ion batteries because of their extremely high capacity. However, poor cycling stability and slow kinetics continue to limit the widespread use of silicon in commercial batteries. Performance improvement has been often demonstrated in nanostructured silicon electrodes, but the reaction mechanisms involved in the electrochemical lithiation of nanoscale silicon are not well understood. Here, in‐situ synchrotron X‐ray diffraction is used to monitor the subtle structural changes occurring in Si nanoparticles in a Si‐C composite electrode during lithiation. Local analysis by electron energy‐loss spectroscopy and transmission electron microscopy is performed to interrogate the nanoscale morphological changes and phase evolution of Si particles at different depths of discharge. It is shown that upon lithiation, Si nanoparticles behave quite differently than their micrometer‐sized counterparts. Although both undergo an electrochemical amorphization, the micrometer‐sized silicon exhibits a linear transformation during lithiation, while a two‐step process occurs in the nanoscale Si. In the first half of the discharge, lithium reacts with surfaces, grain boundaries and planar defects. As the reaction proceeds and the cell voltage drops, lithium consumes the crystalline core transforming it into amorphous LixSi with a primary particle size of just a few nanometers. Unlike the bulk silicon electrode, no Li15Si4 or other crystalline LixSi phases were formed in nanoscale Si at the fully‐lithiated state.  相似文献   

7.
    
Mass dissolution is one main problems for cathodes in aqueous electrolytes due to the strong polarity of water molecules. In principle, mass dissolution is a thermodynamically favorable process as determined by the Gibbs free energy. However, in real situations, dissolution kinetics, which include viscosity, dissolving mass mobility, and interface properties, are also a critical factor influencing the dissolution rate. Both thermodynamic and kinetic dissolving factors can be regulated by the ratio of salt to solvent in the electrolyte. In this study, concentration‐controlled cathode dissolution is investigated in a susceptible Na3V2(PO4)3 cathode whose time‐, cycle‐, and state‐of‐charge‐dependent dissolubility are evaluated by multiple electrochemical and chemical methods. It is verified that the super‐highly concentrated water‐in‐salt electrolyte has a high viscosity, low vanadium ion diffusion, low polarity of solvated water, and scarce solute?water dissolving surfaces. These factors significantly lower the thermodynamic‐controlled solubility and the dissolving kinetics via time and physical space local mass interfacial confinement, thereby inducing a new mechanism of interface concentrated‐confinement which improves the cycling stability in real aqueous rechargeable sodium‐ion batteries.  相似文献   

8.
    
3D batteries continue to be of widespread interest for flexible energy storage where the 3D nanostructured cathode is the key component to achieve both high energy and power densities. While current work on flexible cathodes tends to emphasize the use of flexible scaffolds such as graphene and/or carbon nanotubes, this approach is often limited by poor electrical contact and structural stability. This communication presents a novel synthetic approach to form 3D array cathode for the first time, the single‐crystalline Na3(VO)2(PO4)2F (NVOPF) by using VO2 array as a seed layer. The NVOPF cathode exhibits both high‐rate capability (charge/discharge in 60 s) and long‐term durability (10,000 cycles at 50 C) for Na ion storage. Utilizing in situ X‐ray diffraction and first principles calculations, the high‐rate properties are correlated with the small volume change, 2D fast ion transport, and the array morphology. A novel all‐array flexible Na+ hybrid energy storage device based on pairing the intercalation‐type NVOPF array cathode with a cogenetic pseudocapacitive VO2 nanosheet array anode is demonstrated.  相似文献   

9.
    
Safety has been a major technological concern hindering the deployment of lithium‐ion batteries for automobile applications. We investigated the decomposition mechanism of delithiated cathode materials at thermal abuse conditions using Li1.1[Ni1/3Mn1/3Co1/3]0.9O2 as a model cathode material. An in‐situ high‐energy X‐ray diffraction technique was established as an alternative to conventional thermal analysis techniques like differential scanning calorimetry and accelerating rate calorimetry. The X‐ray diffraction data revealed that the thermal decomposition pathway of delithiated Li1‐x[Ni1/3Mn1/3Co1/3]0.9O2 strongly depended on the exposed chemical environment, like solvents and lithium salts. A phase transformation of dry delithiated Li1‐x[Ni1/3Mn1/3Co1/3]0.9O2 was observed at about 278 °C, and its onset temperature was reduced to about 197°C with the presence of the electrolyte. It is suggested that the reduction in thermal stability is possibly related to proton intercalation into the delithiated material.  相似文献   

10.
    
Sodium‐ion batteries (SIBs) are promising next‐generation alternatives due to the low cost and abundance of sodium sources. Yet developmental electrodes in SIBs such as transition metal sulfides have huge volume expansion, sluggish Na+ diffusion kinetics, and poor electrical conductivity. Here bimetallic sulfide (Co9S8/ZnS) nanocrystals embedded in hollow nitrogen‐doped carbon nanosheets are demonstrated with a high sodium diffusion coefficient, pseudocapacitive effect, and excellent reversibility. Such a unique composite structure is designed and synthesized via a facile sulfidation of the CoZn‐MOFs followed by calcination and is highly dependant on the reaction time and temperature. The optimized Co1Zn1‐S(600) electrode exhibits excellent sodium storage performance, including a high capacity of 542 mA h g?1 at 0.1 A g?1, good rate capability at 10 A g?1, and excellent cyclic stability up to 500 cycles for half‐cell. It also shows potential in full‐cell configuration. Such capabilities will accelerate the adoption of sodium‐ion batteries for electrical energy applications.  相似文献   

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13.
    
Structurally and chemically defective activated‐crumbled graphene (A‐CG) is employed to achieve unique synergy of large reversible potassium (K) and sodium (Na) ion storage capacity with fast charging and extended cyclability. A‐CG synthesis consists of low temperature spraying of graphene oxide slurry, followed by partial reduction annealing and air activation. For K storage, the reversible capacities are 340 mAh g?1 at 0.04 A g?1, 261 mAh g?1 at 0.5 A g?1, and 210 mAh g?1 at 2 A g?1. For Na storage, the reversible capacities are 280 mAh g?1 at 0.04 A g?1, 191 mAh g?1 at 0.5 A g?1, and 151 mAh g?1 at 2 A g?1. A‐CG shows a stable intermediate rate (0.5 Ag?1) cycling with both K and Na, with minimal fade after 2800 and 8000 cycles. These are among the most favorable capacity—rate capability—cyclability combinations recorded for potassium‐ion battery and sodium‐ion battery carbons. Electroanalytical studies (cyclic voltammetry, galvanostatic intermittent titration technique, b‐value) and density functional theory (DFT) reveal that enhanced electrochemical performance originates from ion adsorption at various defects, such as Stone–Wales defects. Moreover, DFT highlights enhanced thermodynamic stability of A‐CG with adsorbed K versus with adsorbed Na, explaining the unexpected higher reversible capacity with the former.  相似文献   

14.
    
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15.
    
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16.
    
Pseudocapacitance is a Faradaic process that involves surface or near surface redox reactions. Increasing the pseudocapacitive contribution is one of the most effective means to improve the rate performance of electrode materials. In this study, graphene oxide is used as a template to in situ synthesize burr globule‐like FeSe2/graphene hybrid (B‐FeSe2/G) using a facile one‐step hydrothermal method. Structural characterization demonstrates that graphene layers not only wrap the surfaces of FeSe2 particles, but also stretch into the interior of these particles, as a result of which the unique nano‐microsphere structure is successfully established. When serving as anode material for Na‐ion batteries, B‐FeSe2/G hybrid displays high electrochemical performance in the voltage range of 0.5–2.9 V. The B‐FeSe2/G hybrid has high reversible capacity of 521.6 mAh·g?1 at 1.0 A g?1. Meanwhile, after 400 cycles, high discharge capacity of 496.3 mAh g?1 is obtained at a rate of 2.5 A g?1, with a high columbic efficiency of 96.6% and less than 1.0% loss of discharge capacity. Even at the ultrahigh rate of 10 A g?1, a specific capacity of 316.8 mAh g?1 can be achieved. Kinetic analyses reveal that the excellent performance of the B‐FeSe2/G hybrid is largely attributed to the high pseudocapacitive contribution induced by the special nano‐micro structure.  相似文献   

17.
    
Nanosized hollandite‐type VO1.75(OH)0.5 is introduced as a novel cathode material for Na‐ion batteries. Structural investigation based on X‐ray diffraction and Rietveld refinement suggests the presence of numerous vacant sites for Na+ intercalation in the VO1.75(OH)0.5 structure. All of the possible Na+ sites and tunnel‐type Na+ diffusion pathways along the c‐axis are confirmed by bond‐valence‐sum analyses. The nanosized hollandite‐type VO1.75(OH)0.5 delivers an unexpectedly high specific capacity of ≈351 mAh g?1 at 15.5 mA g?1 in the voltage range of 1.0–3.7 V (vs Na+/Na), which agrees well with the results predicted by first‐principles calculations. In addition, combined studies using first‐principles calculations and several experimental techniques including in situ operando X‐ray diffraction and ex situ X‐ray absorption spectroscopy confirm that the nanosized hollandite‐type VO1.75(OH)0.5 undergoes a single‐phase reaction with a capacity retention of 71% over 200 cycles. Furthermore, the open structure and nanosized particles of hollandite‐type VO1.75(OH)0.5 contribute to its excellent power capability with 56% of the capacity measured at 0.05 C being delivered at 7 C.  相似文献   

18.
    
Sodium‐ion batteries have attracted ever‐increasing attention in view of the natural abundance of sodium resources. Sluggish sodiation kinetics, nevertheless, remain a tough challenge, in terms of achieving high rate capability and high energy density. Herein, a sheet‐in‐sphere nanoconfiguration of 2D titania–carbon superlattices vertically aligned inside of mesoporous TiO2@C hollow nanospheres is constructed. In such a design, the ultrathin 2D superlattices consist of ordered alternating monolayers of titania and carbon, enabling interpenetrating pathways for rapid transport of electrons and Na+ ions as well as a 2D heterointerface for Na+ storage. Kinetics analysis discloses that the combination of 2D heterointerface and mesoporosity results an intercalation pseudocapacitive charge storage mechanism, which triggers ultrafast sodiation kinetics. In situ transmission electron microscope imaging and in situ synchrotron X‐ray diffraction techniques elucidate that the sheet‐in‐sphere architecture can maintain robust mechanical and crystallographic structural stability, resulting an extraordinary high rate capability, remarkable stable cycling with a low capacity fading ratio of 0.04% per cycle over 500 cycles at 0.2 C, and exceptionally long‐term cyclability up to 20 000 cycles at 50 C. This study offers a method for the realization of a high power density and long‐term cyclability battery by designing of a hierarchical nanoarchitecture.  相似文献   

19.
    
Narrow electrochemical stability window (1.23 V) of aqueous electrolytes is always considered the key obstacle preventing aqueous sodium‐ion chemistry of practical energy density and cycle life. The sodium‐ion water‐in‐salt electrolyte (NaWiSE) eliminates this barrier by offering a 2.5 V window through suppressing hydrogen evolution on anode with the formation of a Na+‐conducting solid‐electrolyte interphase (SEI) and reducing the overall electrochemical activity of water on cathode. A full aqueous Na‐ion battery constructed on Na0.66[Mn0.66Ti0.34]O2 as cathode and NaTi2(PO4)3 as anode exhibits superior performance at both low and high rates, as exemplified by extraordinarily high Coulombic efficiency (>99.2%) at a low rate (0.2 C) for >350 cycles, and excellent cycling stability with negligible capacity losses (0.006% per cycle) at a high rate (1 C) for >1200 cycles. Molecular modeling reveals some key differences between Li‐ion and Na‐ion WiSE, and identifies a more pronounced ion aggregation with frequent contacts between the sodium cation and fluorine of anion in the latter as one main factor responsible for the formation of a dense SEI at lower salt concentration than its Li cousin.  相似文献   

20.
    
The mechanism by which potassium ions are transported through ion channels is currently being investigated by several groups using many different techniques. Clarification of the location of water molecules during transport is central to understanding how these integral membrane proteins function. Neutrons have a unique sensitivity to both hydrogen and potassium, rendering neutron crystallography capable of distinguishing waters from K+ ions. Here, the collection of a complete neutron data set from a potassium ion channel to a resolution of 3.55 Å using the Macromolecular Neutron Diffractometer (MaNDi) is reported. A room‐temperature X‐ray data set was also collected from the same crystal to a resolution of 2.50 Å. Upon further refinement, these results will help to further clarify the ion/water population within the selectivity filter of potassium ion channels.  相似文献   

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