In situ X-ray absorption near edge structure studies and charge transfer kinetics of Na6[V10O28] electrodes.

Polyoxometalates (POMs) have been reported as promising electrode materials for energy storage applications due to their ability to undergo fast redox reactions with multiple transferred electrons per polyanion. Here we employ a polyoxovanadate salt, Na6[V10O28], as an electrode material in a lithium-ion containing electrolyte and investigate the electron transfer properties of Na6[V10O28] on long and short timescales. Looking at equilibrated systems, in situ V K-edge X-ray absorption near edge structure (XANES) studies show that all 10 V5+ ions in Na6[V10O28] can be reversibly reduced to V4+ in a potential range of 4-1.75 V vs. Li/Li+. Focusing on the dynamic response of the electrode to potential pulses, the kinetics of Na6[V10O28] electrodes and the dependence of the fundamental electron transfer rate k0 on temperature are investigated. From these measurements we calculate the reorganization energy and compare it with theoretical predictions. The experimentally determined reorganization energy of λ = 184 meV is in line with the theoretical estimate and confirms the hypothesis of small values of λ for POMs due to electrostatic shielding of the redox center from the solvent.

Constructing hierarchical spheres from large ultrathin anatase TiO2 nanosheets with nearly 100% exposed (001) facets for fast reversible lithium storage.

Synthesis of nanocrystals with exposed high-energy facets is a well-known challenge in many fields of science and technology. The higher reactivity of these facets simultaneously makes them desirable catalysts for sluggish chemical reactions and leads to their small populations in an equilibrated crystal. Using anatase TiO(2) as an example, we demonstrate a facile approach for creating high-surface-area stable nanosheets comprising nearly 100% exposed (001) facets. Our approach relies on spontaneous assembly of the nanosheets into three-dimensional hierarchical spheres, which stabilizes them from collapse. We show that the high surface density of exposed TiO(2) (001) facets leads to fast lithium insertion/deinsertion processes in batteries that mimic features seen in high-power electrochemical capacitors.

New RE microporous heteropolyhedral silicates containing 4(1)5(1)6(1)8(2) tetrahedral sheets.

Four heteropolyhedral microporous silicates, A(3)RESi(6)O(15).2.25H(2)O, crystallizing in the Cmm2 space group and based on 4(1)5(1)6(1)8(2) tetrahedral sheets [A(3) = Na(2.74)K(0.26), RE = Ce, abbreviated as TR05; TR06: A(3) = Na(2.72)K(0.28), RE = La; TR07: A(3) = Na(3), RE = La; TR08: A(3) = Na(2.74)(H(3)O)(0.26), RE = La(0.68)Eu(0.32)] have been hydrothermally synthesized in Teflon-lined autoclaves at 503 K and structurally characterized using X-ray diffraction single-crystal data. Except for TR05, diffraction data have been collected on {001} twins by merohedry. The four structures are isotypic and based on strongly corrugated 4(1)5(1)6(1)8(2) silicate sheets interconnected along [010] by seven-coordinated RE polyhedra to form a microporous heteropolyhedral framework. The framework is crossed by three systems of ellipsoidal channels that host H(2)O molecules and alkaline ions. The channels run either parallel or perpendicular to the silicate sheets; the largest effective channel width is 4.7 x 2 A. In TR08 some (H(3)O)(+) replaces alkalis. Although the H atoms have not been localized, the configuration of the hydrogen bonding has been deduced from bond lengths and angles.

Layered NaxMnO2+z in sodium ion batteries-influence of morphology on cycle performance.

Due to its potential cost advantage, sodium ion batteries could become a commercial alternative to lithium ion batteries. One promising cathode material for this type of battery is layered sodium manganese oxide. In this investigation we report on the influence of morphology on cycle performance for the layered NaxMnO2+z. Hollow spheres of NaxMnO2+z with a diameter of ∼5 µm were compared to flake-like NaxMnO2+z. It was found that the electrochemical behavior of both materials as measured by cyclic voltammetry is comparable. However, the cycle stability of the spheres is significantly higher, with 94 mA h g(-1) discharge capacity after 100 cycles, as opposed to 73 mA h g(-1) for the flakes (50 mA g(-1)). The better stability can potentially be attributed to better accommodation of volume changes of the material due to its spherical morphology, better contact with the added conductive carbon, and higher electrode/electrolyte interface owing to better wetting of the active material with the electrolyte.

Synthesis and enhanced lithium storage properties of electrospun V2O5 nanofibers in full-cell assembly with a spinel Li4Ti5O12 anode.

We have successfully demonstrated the reversible electrochemical Li-insertion properties of electrospun vanadium pentoxide nanofibers (VNF) in full-cell assembly with a Li4Ti5O12 anode. Li-insertion in to VNF is restricted for the intercalation of 1 mol of Li by adjusting lower cutoff potential (2.5-4 V vs Li). The half-cell (Li/VNF) delivered a reversible capacity of ~148 mA h g(-1) with excellent cycleability and capacity retention of over 85% after 30 cycles. Full-cell assembly is conducted for such VNF cathodes after the electrochemical lithiation (LiV2O5) with spinel Li4Ti5O12 anode under the optimized mass loadings. Full-cell (LiV2O5/Li4Ti5O12) delivered an excellent cycleability irrespective of applied current densities with good reversible capacity of ~119 mA h g(-1) (at 20 mA g(-1) current density). This work clearly demonstrates the possibility of using LiV2O5/Li4Ti5O12 configuration for high power applications such as hybrid electric vehicles and electric vehicles in the near future.

Electrospun eggroll-like CaSnO3 nanotubes with high lithium storage performance.

Novel eggroll-like CaSnO(3) nanotubes have been prepared by a single spinneret electrospinning method followed by calcination in air for the first time. The electrospun sample as a lithium-ion battery electrode material exhibited improved cycling stability and rate capability by virtue of the high surface area and unique hollow interior structure, compared to nanorod-structured CaSnO(3).

Facile approach to prepare porous CaSnO3 nanotubes via a single spinneret electrospinning technique as anodes for lithium ion batteries.

CaSnO3 nanotubes are successfully prepared by a single spinneret electrospinning technique. The characterized results indicate that the well-crystallized one-dimensional (1D) CaSnO3 nanostructures consist of about 10 nm nanocrystals, which interconnect to form nanofibers, nanotubes, and ruptured nanobelts after calcination. The diameter and wall thickness of CaSnO3 nanotubes are about 180 and 40 nm, respectively. It is demonstrated that CaSnO3 nanofiber, nanotubes, and ruptured nanobelts can be obtained by adjusting the calcination temperature in the range of 600-800 °C. The effect of calcination temperature on the morphologies of electrospun 1D CaSnO3 nanostructures and the formation mechanism leading to 1D CaSnO3 nanostructures are investigated. As anodes for lithium ion batteries, CaSnO3 nanotubes exhibit superior electrochemical performance and deliver 1168 mAh g⁻¹ of initial discharge capacity and 565 mAh g⁻¹ of discharge capacity up to the 50th cycle, which is ascribed to the hollow interior structure of 1D CaSnO3 nanotubes. Such porous nanotubular structure provides both buffer spaces for volume change during charging/discharging and rapid lithium ion transport, resulting in excellent electrochemical performance.