Microwave-assisted synthesis and electrochemical evaluation of VO2 (B) nanostructures

Understanding how intercalation materials change during electrochemical operation is paramount to optimizing their behaviour and function and in situ characterization methods allow us to observe these changes without sample destruction. Here we first report the improved intercalation properties of bronze phase vanadium dioxide VO2 (B) prepared by a microwave-assisted route which exhibits a larger electrochemical capacity (232 mAh g-1) compared with VO2 (B) prepared by a solvothermal route (197 mAh g-1). These electrochemical differences have also been followed using in situ X-ray absorption spectroscopy allowing us to follow oxidation state changes as they occur during battery operation

Solvation structure and energetics of electrolytes for multivalent energy storage

By analysing X-ray pair distribution function data using a multivariate statistical approach, we isolate the cation solvation structure for monovalent (Li(+)/Na(+)/K(+)) and multivalent (Mg(2+)/Ca(2+)/Zn(2+)) electrolytes based on TFSI salts in diglyme. Parallel molecular dynamics simulations provide enhanced structural details. The data suggest that contact ion-pairs are a common feature in multivalent electrolytes

Constant real-space fractal dimensionality and structure evolution in Ti62Cu38 metallic glass under high pressure

The structure of binary Ti62Cu38 metallic glass is investigated under pressures up to 33.8 GPa using the pair distribution function analysis based on high-energy x-ray scattering and reverse Monte Carlo (RMC) simulations. At a global scale, its relative volume shows a continuously smooth curve as a function of pressure. The isothermal bulk modulus of Ti62Cu38 metallic glass is estimated as B0=132(3)GPa with B0′=5.8(0.4). At a local scale, the atomic packing structure under compression conditions, which is extracted from RMC simulations, shows that the topological short-range order is dominated by the deformed icosahedron polyhedra and basically maintains stable. From the relationship between the relative volume and changing ratio of the atomic separation distances, the real-space fractal dimensionality of this metallic glass is determined as about 2.5 for all of the first four peaks. This experimental result reveals the consistent nature of the fractal feature on the degree of self-similarity in this sample within the entire experimental pressure range

Hydrostatic low-range pressure applications of the Paris–Edinburgh cell utilizing polymer gaskets for diffuse X-ray scattering measurements

The use of a polymeric (Torlon or polyamide–imide) gasket material in a Paris–Edinburgh pressure cell for in situ high-pressure X-ray scattering measurements is demonstrated. The quality of the data obtained in this way is suitable for Bragg and pair distribution function analysis

Identifying the Structure of the Intermediate, Li2/3CoPO4, Formed during Electrochemical Cycling of LiCoPO4.

In situ synchrotron diffraction measurements and subsequent Rietveld refinements are used to show that the high energy density cathode material LiCoPO4 (space group Pnma) undergoes two distinct two-phase reactions upon charge and discharge, both occurring via an intermediate Li2/3(Co2+)2/3(Co3+)1/3PO4 phase. Two resonances are observed for Li2/3CoPO4 with intensity ratios of 2:1 and 1:1 in the 31P and 7Li NMR spectra, respectively. An ordering of Co2+/Co3+ oxidation states is proposed within a (a × 3b × c) supercell, and Li+/vacancy ordering is investigated using experimental NMR data in combination with first-principles solid-state DFT calculations. In the lowest energy configuration, both the Co3+ ions and Li vacancies are found to order along the b-axis. Two other low energy Li+/vacancy ordering schemes are found only 5 meV per formula unit higher in energy. All three configurations lie below the LiCoPO4-CoPO4 convex hull and they may be readily interconverted by Li+ hops along the b-direction.This is the final version. It was first published by ACS Publications at http://pubs.acs.org/doi/abs/10.1021/cm502680

A radially accessible tubular in situ X-ray cell for spatially resolved operando scattering and spectroscopic studies of electrochemical energy storage devices

A tubular operando electrochemical cell has been developed to allow spatially resolved X-ray scattering and spectroscopic measurements of individual cell components, or regions thereof, during device operation. These measurements are enabled by the tubular cell geometry, wherein the X-ray-transparent tube walls allow radial access for the incident and scattered/transmitted X-ray beam; by probing different depths within the electrode stack, the transformation of different components or regions can be resolved. The cell is compatible with a variety of synchrotron-based scattering, absorption and imaging methodologies. The reliability of the electrochemical cell and the quality of the resulting X-ray scattering and spectroscopic data are demonstrated for two types of energy storage: the evolution of the distribution of the state of charge of an Li-ion battery electrode during cycling is documented using X-ray powder diffraction, and the redistribution of ions between two porous carbon electrodes in an electrochemical double-layer capacitor is documented using X-ray absorption near-edge spectroscopy

Adsorbate-induced structural changes in 1-3 nm platinum nanoparticles

We investigated changes in the Pt–Pt bond distance, particle size, crystallinity, and coordination of Pt nanoparticles as a function of particle size (1–3 nm) and adsorbate (H2, CO) using synchrotron radiation pair distribution function (PDF) and X-ray absorption spectroscopy (XAS) measurements. The ∼1 nm Pt nanoparticles showed a Pt–Pt bond distance contraction of ∼1.4%. The adsorption of H2 and CO at room temperature relaxed the Pt–Pt bond distance contraction to a value close to that of bulk fcc Pt. The adsorption of H2 improved the crystallinity of the small Pt nanoparticles. However, CO adsorption generated a more disordered fcc structure for the 1–3 nm Pt nanoparticles compared to the H2 adsorption Pt nanoparticles. In situ XANES measurements revealed that this disorder results from the electron back-donation of the Pt nanoparticles to CO, leading to a higher degree of rehybridization of the metal orbitals in the Pt-adsorbate system

A thermal‐gradient approach to variable‐temperature measurements resolved in space

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155923/1/jcr2te5056.pd

Lithiation Thermodynamics and Kinetics of the TiO2 (B) Nanoparticles

TiO2 (B) has attracted considerable attention in recent years because it exhibits the largest capacity among all studied titania polymorphs, with high rate performance for Li intercalation being achieved when this material is nanostructured. However, due to the complex nature of its lithiation mechanism and practical challenges in probing Li structure in nanostructured materials, a definitive understanding of the lithiation thermodynamics has yet to be established. A comprehensive mechanistic investigation of the TiO2 (B) nanoparticles is therefore presented using a combination of in situ / operando X-ray pair distribution function (PDF) and electrochemical techniques. The discharge begins with surface reactions in parallel with Li insertion into the sub-surface of the nanoparticles. The Li bulk insertion starts with a single-phase reaction into the A2 site, a position adjacent to the b-channel. A change of the Li diffusion pathway from that along this open channel to that along the c-direction is likely to occur at the composition of Li0.25TiO2 until Li0.5TiO2 is attained, leading to a two-step A2-site incorporation with one step kinetically distinct from the other. Subsequent Li insertion involves the C’ site, a position situated inside the channel, and follows a rapid two-phase reaction to form Li0.75TiO2. Due to the high diffusion barrier associated with the further lithiation, Li insertion into the A1 site, another position adjacent to the channel neighboring the A2 sites, is kinetically restricted. This study not only explores the lithiation reaction thermodynamics and mechanisms of nanoparticulate TiO2 (B), but also serves as a strong reference for future studies of the bulk phase, and for future calculations to study the Li transport properties of TiO2 (B).We acknowledge the funding from the Swiss NRP70 “Energy Turnaround” program and EPSRC via the “nanoionics” grant. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Journal of the American Chemical Society Article Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02- 06CH11357