MnFe2O4 nanodots (∼3.3 nm) homogeneously dispersed in porous nitrogen-doped carbon nanofibers (denoted as MFO@C) were prepared by a feasible electrospinning technique. Meanwhile, MFO@C with the ...character of flexible free-standing membrane was directly used as binder- and current collector-free anode for sodium-ion batteries, exhibiting high electrochemical performance with high-rate capability (305 mA h g–1 at 10000 mA g–1 in comparison of 504 mA h g–1 at 100 mA g–1) and ultralong cycling life (ca. 90% capacity retention after 4200 cycles). The Na-storage mechanism was systematically studied, revealing that MnFe2O4 is converted into metallic Mn and Fe after the first discharge (MnFe2O4 + 8Na+ + 8e– → Mn + 2Fe + 4Na2O) and then to MnO and Fe2O3 during the following charge (Mn + 2Fe + 4Na2O → MnO + Fe2O3 + 8Na+ + 8e–). The subsequent cycles occur through reversible redox reactions of MnO + Fe2O3 + 8Na+ + 8e– ↔ Mn + 2Fe + 4Na2O, of which the reduction/oxidation of MnO/Mn takes place at a lower potential than that of Fe2O3/Fe. Furthermore, a soft package sodium-ion full battery with MFO@C anode and Na3V2(PO4)2F3/C cathode was assembled, delivering a stable capacity of ∼400 mA h g–1 for MFO@C (with 100 cycles at 500 mA g–1) and a promising energy density of 77.8 Wh kg–1 for the whole battery. This is owing to the distinctive structure of very-fine MnFe2O4 nanodots embedded in porous N-doped carbon nanofibers, which effectively improves the utilization rate of active materials, facilitates the transportation of electrons and Na+ ions, and prevents the particle pulverization/agglomeration upon prolonged cycling.
Designed as a high‐capacity, high‐rate, and long‐cycle life anode for sodium‐ion batteries, ultrasmall Sn nanoparticles (≈8 nm) homogeneously embedded in spherical carbon network (denoted as 8‐Sn@C) ...is prepared using an aerosol spray pyrolysis method. Instrumental analyses show that 8‐Sn@C nanocomposite with 46 wt% Sn and a BET surface area of 150.43 m2 g−1 delivers an initial reversible capacity of ≈493.6 mA h g−1 at the current density of 200 mA g−1, a high‐rate capacity of 349 mA h g−1 even at 4000 mA g−1, and a stable capacity of ≈415 mA h g−1 after 500 cycles at 1000 mA g−1. The remarkable electrochemical performance of 8‐Sn@C is owing to the synergetic effects between the well‐dispersed ultrasmall Sn nanoparticles and the conductive carbon network. This unique structure of very‐fine Sn nanoparticles embedded in the porous carbon network can effectively suppress the volume fluctuation and particle aggregation of tin during prolonged sodiation/desodiation process, thus solving the major problems of pulverization, loss of electrical contact and low utilization rate facing Sn anode.
Sn@C composite with ultrasmall Sn nanoparticles (≈8 nm) homogeneously embedded in spherical carbon network is prepared by aerosol spray pyrolysis, and further evaluated as anode material for rechargeable Na‐ion batteries. The nanocomposite exhibits excellent electrochemical performance with high reversible capacity, high‐rate capability, and long cycling stability.
Rechargeable aqueous Zn-ion batteries are attractive cheap, safe and green energy storage technologies but are bottlenecked by limitation in high-capacity cathode and compatible electrolyte to ...achieve satisfactory cyclability. Here we report the application of nonstoichiometric ZnMn2O4/carbon composite as a new Zn-insertion cathode material in aqueous Zn(CF3SO3)2 electrolyte. In 3 M Zn(CF3SO3)2 solution that enables ∼100% Zn plating/stripping efficiency with long-term stability and suppresses Mn dissolution, the spinel/carbon hybrid exhibits a reversible capacity of 150 mAh g–1 and a capacity retention of 94% over 500 cycles at a high rate of 500 mA g–1. The remarkable electrode performance results from the facile charge transfer and Zn insertion in the structurally robust spinel featuring small particle size and abundant cation vacancies, as evidenced by combined electrochemical measurements, XRD, Raman, synchrotron X-ray absorption spectroscopy, FTIR, and NMR analysis. The results would enlighten and promote the use of cation-defective spinel compounds and trifluoromethanesulfonic electrolyte to develop high-performance rechargeable zinc batteries.
Abstract
With excellent creep resistance, good high-temperature microstructural stability and good irradiation resistance, oxide dispersion strengthened (ODS) alloys are a class of important alloys ...that are promising for high-temperature applications. However, plagued by a nerve-wracking fact that the oxide particles tend to aggregate at grain boundary of metal matrix, their improvement effect on the mechanical properties of metal matrix tends to be limited. In this work, we employ a unique in-house synthesized oxide@W core-shell nanopowder as precursor to prepare W-based ODS alloy. After low-temperature sintering and high-energy-rate forging, high-density oxide nanoparticles are dispersed homogeneously within W grains in the prepared alloy, accompanying with the intergranular oxide particles completely disappearing. As a result, our prepared alloy achieves a great enhancement of strength and ductility at room temperature. Our strategy using core-shell powder as precursor to prepare high-performance ODS alloy has potential to be applied to other dispersion-strengthened alloy systems.
Aqueous Zn‐storage behaviors of MoS2‐based cathodes mainly rely on the ion‐(de)intercalation at edge sites but are limited by the inactive basal plane. Herein, an in‐situ molecular engineering ...strategy in terms of structure defects manufacturing and O‐doping is proposed for MoS2 (designated as D‐MoS2‐O) to unlock the inert basal plane, expand the interlayer spacing (from 6.2 to 9.6 Å), and produce abundant 1T‐phase. The tailored D‐MoS2‐O with excellent hydrophilicity and high conductivity allows the 3D Zn2+ transport along both the ab plane and c‐axis, thus achieving the exceptional high rate capability. Zn2+ diffusion through the basal plane is verified by DFT computations. As a proof of concept, the wearable quasi‐solid‐state rechargeable Zn battery employing the D‐MoS2‐O cathode operates stably even under severe bending conditions, showing great application prospects. This work opens a new window for designing high‐performance layered cathode materials for aqueous Zn‐ion batteries.
In‐situ molecular engineering of structure defect manufacturing and O‐doping unlocks the MoS2 basal plane and simultaneously upgrades its interlayer spacing (from 6.2 to 9.6 Å), hydrophilicity, and electrical conductivity. These merits enable highly efficient 3D Zn‐ion transport in the MoS2 lattice along both the ab plane and c‐axis, thus leading to fast reaction kinetics and the exceptional rate performance in aqueous Zn‐ion batteries.
Sodium‐ion batteries (SIBs) have attracted incremental attention as a promising candidate for grid‐scale energy‐storage applications. To meet practical requirements, searching for new cathode ...materials with high energy density is of great importance. Herein, a novel Na superionic conductor (NASICON)‐type Na4MnCr(PO4)3 is developed as a high‐energy cathode for SIBs. The Na4MnCr(PO4)3 nanoparticles homogeneously embedded in a carbon matrix can present an extraordinary reversible capacity of 160.5 mA h g−1 with three‐electron reaction at ≈3.53 V during the Na+ extraction/insertion process, realizing an unprecedentedly high energy density of 566.5 Wh kg−1 in the phosphate cathodes for SIBs. It is intriguing to reveal the underlying mechanism of the unique Mn2+/Mn3+, Mn3+/Mn4+, and Cr3+/Cr4+ redox couples via X‐ray absorption near‐edge structure spectroscopy. The whole electrochemical reaction undergoes highly reversible single‐phase and biphasic transitions with a moderate volume change of 7.7% through in situ X‐ray diffraction and ex situ high‐energy synchrotron X‐ray diffraction. Combining density functional theory (DFT) calculations with the galvanostatic intermittent titration technique, the superior performance is ascribed to the low ionic‐migration energy barrier and desirable Na‐ion diffusion kinetics. The present work can offer a new insight into the design of multielectron‐reaction cathode materials for SIBs.
A novel NASICON‐type Na4MnCr(PO4)3 cathode presents an unusual reversible Mn2+/Mn3+, Mn3+/Mn4+, and Cr3+/Cr4+ three‐electron reaction with a moderate volume change during Na+ extraction/insertion, enabling an unprecedentedly high energy density in polyanionic cathode materials for sodium‐ion batteries.
Maricite NaFePO4 nanodots with minimized sizes (≈1.6 nm) uniformly embedded in porous N‐doped carbon nanofibers (designated as NaFePO4@C) are first prepared by electrospinning for maximized ...Na‐storage performance. The obtained flexible NaFePO4@C fiber membrane adherent on aluminum foil is directly used as binder‐free cathode for sodium‐ion batteries, revealing that the ultrasmall nanosize effect as well as a high‐potential desodiation process can transform the generally perceived electrochemically inactive maricite NaFePO4 into a highly active amorphous phase; meanwhile, remarkable electrochemical performance in terms of high reversible capacity (145 mA h g−1 at 0.2 C), high rate capability (61 mA h g−1 at 50 C), and unprecedentedly high cyclic stability (≈89% capacity retention over 6300 cycles) is achieved. Furthermore, the soft package Na‐ion full battery constructed by the NaFePO4@C nanofibers cathode and the pure carbon nanofibers anode displays a promising energy density of 168.1 Wh kg−1 and a notable capacity retention of 87% after 200 cycles. The distinctive 3D network structure of very fine NaFePO4 nanoparticles homogeneously encapsulated in interconnected porous N‐doped carbon nanofibers, can effectively improve the active materials' utilization rate, facilitate the electrons/Na+ ions transport, and strengthen the electrode stability upon prolonged cycling, leading to the fascinating Na‐storage performance.
Maricite NaFePO4 nanodots with minimized sizes (≈1.6 nm) are homogeneously encapsulated in porous N‐doped carbon nanofibers by electrospinning. When evaluated as binder‐free cathode for Na‐ion batteries, the ultrasmall nanosize effect with a high‐potential desodiation process successfully transforms the generally perceived electrochemically inactive maricite NaFePO4 into a highly active amorphous phase, rendering high reversible capacity, exceptional rate‐capability, and unprecedentedly long cycle‐life.
•Direct diffusion bonding method is a feasible way to construct a metallurgical bonding interface between immiscible W and Cu.•The key point of the direct diffusion bonding is that bonding ...temperatures should be close to copper's melting point.•The maximum tensile and bending strengths of the obtained W/Cu joints are about 172MPa and 232MPa, respectively.•A diffusion occurs between W and Cu and the thickness of the W/Cu diffusion layer is about 22nm.
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In this study, a direct diffusion bonding method is designed to bond tungsten (W) and copper (Cu) without using an interlayer metal at a temperature close to the melting point of copper (TmCu). The results show that the direct diffusion bonding method is feasible and the key point to a successful connection is that bonding temperatures should be controlled in an effective temperature range 0.81TmCu–0.97TmCu. The most appropriate bonding parameters are that the bonding temperature is 980°C, the bonding time is 180min and the bonding pressure is 106MPa. The maximum tensile and bending strengths of the as-obtained W/Cu joints are ~172 and ~232MPa, respectively, which reach a very high level compared to pure copper. The corresponding fractures are ductile. The micro-tests for the W/Cu joint show that diffusion occurs between W and Cu and the thickness of the W/Cu diffusion layer is ~22nm. Through the diffusion, a metallurgical bonding interface has been successfully constructed, which is the essential reason for the high strengths of the W/Cu joint. The diffusion between W and Cu when the bonding temperature is close to TmCu may be induced by the high-temperature structure of Cu, which needs further investigation.
NASICON (Na superionic conductor)-type cathode materials for sodium-ion batteries (SIBs) have attracted extensive attention due to their mechanically robust three-dimensional (3D) framework, which ...has sufficient open channels for fast Na+ transportation. However, they usually suffer from inferior electronic conductivity and low capacity, which severely limit their practical applications. To solve these issues, we need to deeply understand the structural evolution, redox mechanisms, and electrode/electrolyte interface reactions during cycling. Recently, rapid developments in synchrotron X-ray techniques, neutron-based resources, magnetic resonance, as well as optical and electron microscopy have brought numerous opportunities to gain deep insights into the Na-storage behaviors of NASICON cathodes. In this review, we summarize the detection principles of advanced characterization techniques used with typical NASICON-structured cathode materials for SIBs. The special focus is on both operando and ex situ techniques, which help to investigate the relationships among phase, composition, and valence variations within electrochemical responses. Fresh electrochemical measurements and theoretical computations are also included to reveal the kinetics and energy-storage mechanisms of electrodes upon charge/discharge. Finally, we describe potential new developments in NASICON-cathodes with optimized SIB systems, foreseeing a bright future for them, achievable through the rational application of advanced diagnostic methods.
Advanced characterizations and measurements to investigate the NASICON-type cathode materials for sodium-ion batteries are comprehensively summarized from three aspects: i) materials characterization techniques; ii) electrochemical measurements; and iii) theoretical computation technologies. This review helps to understand the in-depth reaction mechanisms behind performance and provides a rational guidance for the future design of promising Na-storage NASICON cathodes with the assistance of advanced diagnostic methods. Display omitted
•The advanced characterizations and measurements for SIBs with NASICON-type cathodes have been comprehensively summarized.•The detection principles of advanced characterization/measurement techniques have been deeply discussed.•Both operando and ex situ techniques have been highlighted to understand the structure-mechanism-performance correlations.•Challenges and promises in developing high-performance NASICON-cathodes with advanced techniques are outlined.
High strength low alloy (HSLA) steels have been widely used in pipelines, power plant components, civil structures and so on, due to their outstanding mechanical properties as high strength and ...toughness, and excellent weldability. Multi-phase microstructures containing acicular ferrite or acicular ferrite dominated phase have been proved to possess good comprehensive properties in HSLA steels. This paper mainly focuses on the formation mechanisms and control methods of acicular ferrite in HSLA steels. Effect of austenitizing conditions, continuous cooling rate, and isothermal quenching time and temperature on acicular ferrite transformation was reviewed. Furthermore, the modified process to control the formation of multi-phase microstructures containing acicular ferrite, as intercritical heat treatments, step quenching treatments and thermo-mechanical controlled processing, was summarized. The favorable combination of mechanical properties can be achieved by these modified treatments.
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