Conductive framework of inverse opal structure for sulfur cathode in lithium-sulfur batteries

As a promising cathode inheritor for lithium-ion batteries, the sulfur cathode exhibits very high theoretical volumetric capacity and energy density. In its practical applications, one has to solve the insulating properties of sulfur and the shuttle effect that deteriorates cycling stability. The state-of-the-art approaches are to confine sulfur in a conductive matrix. In this work, we utilize monodisperse polystyrene nanoparticles as sacrificial templates to build polypyrrole (PPy) framework of an inverse opal structure to accommodate (encapsulate) sulfur through a combined in situ polymerization and melting infiltration approach. In the design, the interconnected conductive PPy provides open channels for sulfur infiltration, improves electrical and ionic conductivity of the embedded sulfur, and reduces polysulfide dissolution in the electrolyte through physical and chemical adsorption. The flexibility of PPy and partial filling of the inverse opal structure endure possible expansion and deformation during long-term cycling. It is found that the long cycling stability of the cells using the prepared material as the cathode can be substantially improved. The result demonstrates the possibility of constructing a pure conductive polymer framework to accommodate insulate sulfur in ion battery applications

Conductive framework of inverse opal structure for sulfur cathode in lithium-sulfur batteries

As a promising cathode inheritor for lithium-ion batteries, the sulfur cathode exhibits very high theoretical volumetric capacity and energy density. In its practical applications, one has to solve the insulating properties of sulfur and the shuttle effect that deteriorates cycling stability. The state-of-the-art approaches are to confine sulfur in a conductive matrix. In this work, we utilize monodisperse polystyrene nanoparticles as sacrificial templates to build polypyrrole (PPy) framework of an inverse opal structure to accommodate (encapsulate) sulfur through a combined in situ polymerization and melting infiltration approach. In the design, the interconnected conductive PPy provides open channels for sulfur infiltration, improves electrical and ionic conductivity of the embedded sulfur, and reduces polysulfide dissolution in the electrolyte through physical and chemical adsorption. The flexibility of PPy and partial filling of the inverse opal structure endure possible expansion and deformation during long-term cycling. It is found that the long cycling stability of the cells using the prepared material as the cathode can be substantially improved. The result demonstrates the possibility of constructing a pure conductive polymer framework to accommodate insulate sulfur in ion battery applications.ISSN:2045-232

Eye and Head Movements in Novice Baseball Players versus Intercollegiate Baseball Players

ISSN:1936-0851ISSN:1936-086

Tailoring Two Polymorphs of LiFePO₄ by Efficient Microwave-Assisted Synthesis: A Combined Experimental and Theoretical Study

LiFePO₄ typically crystallizes in the olivine-type phase (denoted as α-phase hereafter). When high pressure (65 kbar) and elevated temperature (900 °C) are applied, the α-LiFePO₄ transforms into a high-pressure phase (denoted as β-phase hereafter). Here, we report a facile approach to directly tailor the two polymorphs of LiFePO₄ in a controlled way under mild conditions. Employing a microwave-assisted nonaqueous route, highly crystalline LiFePO₄ with either α- or β-phase can be efficiently synthesized within 3 min, by simply tuning the ratio of the solvents, benzyl alcohol, and 2-pyrrolidinone. The resulting β-LiFePO₄ particles exhibit a hierarchical self-assembled bow-tie-like microstructure, whereas the α-phase consists of nanoplates. In addition, the β-phase irreversibly transforms into the α-phase upon heat treatment without alteration of the morphology. After carbon-coating, α-LiFePO₄ and phase-transformed β-LiFePO₄, that is, α-LiFePO₄ with the hierarchical morphology of the β-phase, exhibit excellent electrochemical performance, whereas pristine β-LiFePO₄ displays unfavorable properties. Density functional total energy calculations are performed to get the relative energies and lattice stability of the two phases. A qualitative understanding of the poor electrochemical performance of the β-phase can be deduced from the molecular dynamics of the mobile Li ions in both structures

El Correo gallego : diario político de la mañana: Ano L Número 17779 - 1928 outubro 6

Anatase TiO₂ is among the most studied photocatalytic materials for solar energy conversion and environmental cleanup. However, its poor visible light absorption and high facet-dependent performance limits its utilization. In this study chemical substitution (doping) of TiO₂ nanoparticles with metal ions (Sb, Cr, or Sb/Nb and Cr/Nb) is presented as an alternative strategy to address both issues simultaneously. Highly crystalline doped and codoped TiO₂ nanoparticles were successfully synthesized by a microwave-assisted nonaqueous sol–gel synthesis. The structural and compositional analysis done by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS) showed that depending on the doping applied, variations in particles size and morphology were observed. Doped and codoped samples showed improved absorption in the visible range and in comparison to the undoped TiO₂ displayed improved photocatalytic (PC) activity. The variations of the PC activity, observed among different samples, are attributed to the effect of doping on (i) particles size/morphology, (ii) optical activity, and (iii) on the surface potential differences for the various crystal facets. We found that Sb-doping in TiO₂ diminishes the surface potential difference for {101} reductive and {001} oxidative sites, which makes all crystal surfaces equally attractive to both electrons and holes. Accordingly, in Sb-doped TiO₂ nanoparticles the photocatalytic activity is independent of the exposed crystal facets and thus on the particle morphology. This observation also explains the superior PC performance of this material

A General Method of Fabricating Flexible Spinel-Type Oxide/Reduced Graphene Oxide Nanocomposite Aerogels as Advanced Anodes for Lithium-Ion Batteries

High-capacity anode materials for lithium ion batteries (LIBs), such as spinel-type metal oxides, generally suffer from poor Li⁺ and e^– conductivities. Their drastic crystal structure and volume changes, as a result of the conversion reaction mechanism with Li, severely impede the high-rate and cyclability performance toward their practical application. In this article, we present a general and facile approach to fabricate flexible spinel-type oxide/reduced graphene oxide (rGO) composite aerogels as binder-free anodes where the spinel nanoparticles (NPs) are integrated in an interconnected rGO network. Benefiting from the hierarchical porosity, conductive network and mechanical stability constructed by interpenetrated rGO layers, and from the pillar effect of NPs in between rGO sheets, the hybrid system synergistically enhances the intrinsic properties of each component, yet is robust and flexible. Consequently, the spinel/rGO composite aerogels demonstrate greatly enhanced rate capability and long-term stability without obvious capacity fading for 1000 cycles at high rates of up to 4.5 A g^–1 in the case of CoFe₂O₄. This electrode design can successfully be applied to several other spinel ferrites such as MnFe₂O₄, Fe₃O₄, NiFe₂O₄ or Co₃O₄, all of which lead to excellent electrochemical performances

Solid-State Calcium-Ion Diffusion in Ca1.5Ba0.5Si5O3N6

Rechargeable batteries based on multivalent working ions are promising candidates for next-generation high-energy-density batteries. Development of these technologies, however, is largely limited by the low diffusion rate of multivalent ions in solid-state materials, thereby necessitating a better understanding of the design principles that control multivalent-ion mobility. Here, we report Ca1.5Ba0.5Si5O3N6 as a potential calcium solid-state conductor and investigate its Ca migration mechanism by means of ab initio computations and neutron diffraction. This compound contains partially occupied Ca sites in close proximity to each other, providing a unique mechanism for Ca migration. Nuclear density maps obtained with the maximum entropy method from neutron powder diffraction data provide strong evidence for low-energy percolating one-dimensional pathways for Ca-ion migration. Ab initio molecular dynamics simulations further support a low Ca-ion migration barrier of ∼400 meV when Ca vacancies are present and reveal a unique "vacancy-adjacent"concerted ion migration mechanism. This work provides a new understanding of solid-state Ca-ion diffusion and insights into the future design of novel cation configurations that utilize the interactions between mobile ions to enable fast multivalent-ion conduction in solid-state materials

Promises and Challenges of Next-Generation "Beyond Li-ion" Batteries for Electric Vehicles and Grid Decarbonization.

The tremendous improvement in performance and cost of lithium-ion batteries (LIBs) have made them the technology of choice for electrical energy storage. While established battery chemistries and cell architectures for Li-ion batteries achieve good power and energy density, LIBs are unlikely to meet all the performance, cost, and scaling targets required for energy storage, in particular, in large-scale applications such as electrified transportation and grids. The demand to further reduce cost and/or increase energy density, as well as the growing concern related to natural resource needs for Li-ion have accelerated the investigation of so-called "beyond Li-ion" technologies. In this review, we will discuss the recent achievements, challenges, and opportunities of four important "beyond Li-ion" technologies: Na-ion batteries, K-ion batteries, all-solid-state batteries, and multivalent batteries. The fundamental science behind the challenges, and potential solutions toward the goals of a low-cost and/or high-energy-density future, are discussed in detail for each technology. While it is unlikely that any given new technology will fully replace Li-ion in the near future, "beyond Li-ion" technologies should be thought of as opportunities for energy storage to grow into mid/large-scale applications