cathode material was prepared by the sol-gel method. The material was coated with the ionic conductor Li 3 VO 4 via direct reaction with NH 4 VO 3 at 350 C. The Li 3 VO 4 coated material had a higher ordered hexagonal layered structure, and less Li + /Ni 2+ cation mixing. The surface of the coated material was composed of Li 3 VO 4 polycrystals, which were impregnated into the bulk of the active material. The surface coating protected the material from contact with CO 2 in the air, thus inhibiting the formation of an Li 2 CO 3 layer. Electrochemical studies showed that the Li 3 VO 4 surface coating improved the activation of Mn 4+ ions, resulting in a high discharge capacity. It also prohibited the growth of a solid electrolyte interface film, and facilitated the charge transfer reactions at the electrode/electrolyte interface, thus improving the rate capability and cycle stability of the material. DSC analysis of the fully charged electrode showed that the temperature of the exothermic peak increased from 205.2 C to 232.8 C, and that the amount of heat that was released was reduced from 807.5 J g À1 to 551.0 J g À1 , highlighting the improved thermal stability of the material after coating with Li 3 VO 4 .
H2V3O8 nanowires wrapped by reduced graphene oxide (RGO) are synthesized successfully through a simple hydrothermal process. The structural properties of the samples are characterized by X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman scattering, and X‐ray photoelectron spectroscopy. The RGO nanosheets modify the surfaces of the H2V3O8 nanowires through VC linkages. The H2V3O8/RGO composite exhibits a remarkably enhanced electrochemical performance in terms of its reversible capacity, cyclic performance, and rate capability. The material shows high discharge capacities of 256 and 117 mA h g−1 at the current densities of 0.1 and 1 A g−1, respectively, with almost no capacity fading after fifty charge/discharge cycles. Cyclic voltammetry and electrochemical impedance spectroscopy show that the superior electrochemical performance of H2V3O8/RGO can be attributed to the cooperation of RGO, which provides better mechanical flexibility, higher electronic conductivity, and smaller charge‐transfer resistance.
Multicomponent alloying has displayed extraordinary potential for producing exceptional structural and functional materials. However, the synthesis of single-phase, multiprincipal covalent compounds remains a challenge. Here we present a diffusioncontrolled alloying strategy for the successful realization of covalent multi-principal transition metal carbides (MPTMCs) with a single face-centered cubic (FCC) phase. The increased interfacial diffusion promoted by the addition of a nonstoichiometric compound leads to rapid formation of the new single phase at much lower sintering temperature.Direct atomic-level observations via scanning transmission electron microscopy demonstrate that MPTMCs are composed of a single phase with a random distribution of all cations, which holds the key to the unique combinations of improved fracture toughness, superior Vickers hardness, and extremely lower thermal diffusivity achieved in MPTMCs. The present discovery provides a promising approach toward the design and synthesis of next-generation high-performance materials.
At low temperatures most metals show reduced ductility and impact toughness. Here, we report a compositionally lean, fine-grained Fe-30Mn-0.11C austenitic steel that breaks this rule, exhibiting an increase in strength, elongation and Charpy impact toughness with decreasing temperature. A Charpy impact energy of 453 J is achieved at liquid nitrogen temperatures, which is about four to five times that of conventional cryogenic austenitic steels. The high toughness is attributed to manganese and carbon austenite stabilizing elements, coupled with a reduction in grain size to the near-micrometer scale. Under these conditions dislocation slip and deformation twinning are the main deformation mechanisms, while embrittlement by α′- and ε-martensite transformations are inhibited. This reduces local stress and strain concentration, thereby retarding crack nucleation and prolonging work-hardening. The alloy is low-cost and can be processed by conventional production processes, making it suitable for low-temperature applications in industry.
A one-pot solvothermal approach has been developed for the synthesis of single-crystal anatase TiO2 nanospindles. The introduction of adscititious water in nonaqueous reaction mixture is critical for the spindle formation by allowing for a slow growth rate of TiO2 to facilitate the shape control of TiO2 nanospindles. Arising from the prominent light scattering effect, the fabricated dye sensitized solar cells with the TiO2 nanospindles as light scattering layer show a 27% increment of energy conversion efficiency compared to that of P25 single layer film.
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