Synthesis, Structure Refinement and Chromate Sorption Characteristics of an Al-Rich Bayerite-Based Layered Double Hydroxide

“Imbibition” of Zn2+ ions into the cation vacancies of bayerite–Al(OH)3 and NO3- ions into the interlayer gallery yields an Al-rich layered double hydroxide with Al/Zn ratio ~3. NO3- ions are intercalated with their molecular planes inclined at an angle to the plane of the metal hydroxide slab and bonded to it by hydrogen bonds. Rietveld refinement of the structure shows that the monoclinic symmetry of the precursor bayerite is preserved in the product, showing that the imbibition is topochemical in nature. The nitrate ion is labile and is quantitatively replaced by CrO42- ions from solution. The uptake of CrO42- ions follows a Langmuir adsorption isotherm, thus showing that the hydroxide is a candidate material for green chemistry applications for the removal of CrO42- ions from waste water. Rietveld refinement of the structure of the hydroxide after CrO42- inclusion reveals that the CrO42- ion is intercalated with one of its 2-fold axes parallel to the b-crystallographic axis of the crystal, also the principal 2 axis of the monoclinic cell

Natural abundance solid-state 33S NMR study of NbS3: applications for battery conversion electrodes.

We report ultra-wideline, high-field natural abundance solid-state 33S NMR spectra of the Li-ion battery conversion electrode NbS3, the first 33S NMR study of a compound containing disulfide (S22-) units. The large quadrupolar coupling parameters (CQ ≈ 31 MHz) are consistent with values obtained from DFT calculations, and the spectra provide evidence for the linear Peierls distortion that doubles the number of 33S sites

Evolution of lithium ordering with (de)-lithiation in β- LiVOPO4: Insights through solid state NMR and first principles DFT calculations

The lithium ion battery cathode material β-VOPO4 is capable of intercalating more than one Li ion per transition metal ion due to the accessibility of both the V5+/V4+ and V4+/V3+ redox couples at ~4.5 V and ~2.3 V vs. Li, respectively, giving a theoretical capacity greater than ~300 mAh g−1. The ability to perform full and reversible two Li-ion intercalation in this material, however, has been a matter of debate and the poor crystallinity of the fully lithiated phase has thus far precluded its complete structural characterization by conventional diffraction-based methods. In this work, 7Li and 31P NMR spectroscopy, in combination with first principles DFT calculations, indicate that chemical lithiation results in a single phase β-Li2VOPO4 exhibiting a complex Li ordering scheme with lithium ions occupying multiple disordered environments. 2D NMR 7Li correlation experiments were used to deduce the most likely Li ordering for the β-Li2VOPO4 phase from amongst several DFT optimised structures. In contrast, electrochemically lithiated β-Li2-xVOPO4 discharged to 1.6 V exhibits, in addition to β-Li2VOPO4, a β-Li1.5VOPO4 phase. The existence of β-Li1.5VOPO4 is not reflected in the flat galvanostatic charge and discharge curves nor is evident from diffraction-based methods due to the very close structural similarity between the β-Li1.5VOPO4 phase and β-Li2VOPO4 phases. We demonstrate that solid state NMR spectroscopy, in combination with DFT results provides a powerful tool for identifying intermediate states formed during charge/discharge of these complex phosphates as these phases can be distinguished from the end member phases primarily by the nature of the lithium ordering.NECCES, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0012583

Exploring Cation-Anion Redox Processes in One-Dimensional Linear Chain Vanadium Tetrasulfide Rechargeable Magnesium Ion Cathodes.

For magnesium ion batteries (MIBs) to be used commercially, new cathodes must be developed that show stable reversible Mg intercalation. VS4 is one such promising material, with vanadium and disulfide anions [S2]2- forming one-dimensional linear chains, with a large interchain spacing (5.83 Å) enabling reversible Mg insertion. However, little is known about the details of the redox processes and structural transformations that occur upon Mg intercalation and deintercalation. Here, employing a suite of local structure characterization methods including X-ray photoelectron spectroscopy (XPS), V and S X-ray absorption near-edge spectroscopy (XANES), and 51V Hahn echo and magic-angle turning with phase-adjusted sideband separation (MATPASS) NMR, we show that the reaction proceeds via internal electron transfer from V4+ to [S2]2-, resulting in the simultaneous and coupled oxidation of V4+ to V5+ and reduction of [S2]2- to S2-. We report the formation of a previously unknown intermediate in the Mg-V-S compositional space, Mg3V2S8, comprising [VS4]3- tetrahedral units, identified by using density functional theory coupled with an evolutionary structure-predicting algorithm. The structure is verified experimentally via X-ray pair distribution function analysis. The voltage associated with the competing conversion reaction to form MgS plus V metal directly is similar to that of intermediate formation, resulting in two competing reaction pathways. Partial reversibility is seen to re-form the V5+ and S2- containing intermediate on charging instead of VS4. This work showcases the possibility of developing a family of transition metal polychalcogenides functioning via coupled cationic-anionic redox processes as a potential way of achieving higher capacities for MIBs.S. D. acknowledges DST Overseas Visiting Fellowship in Nano Science and Technology, Government of India (July 2018− June 2019) and EPSRC Programme Grant (EP/M009521/1) for fellowships and funding. This work used the ARCHER UK National Super-computing Service (http://www.archer.ac.uk). This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, and the Scientific Data and Computing Center, a component of the Computational Science Initiative, at Brookhaven National Laboratory under Contract No. DE-SC0012704. The XPS data collection was performed at the EPSRC National Facility for XPS ("HarwellXPS"), operated by Cardiff University and UCL, under Contract No. PR16195. via our membership of the UK's HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202)

A high-performance solid-state synthesized LiVOPO4 for lithium-ion batteries

Funding Information: This research was funded by U.S. Department of Energy , Office of Energy Efficiency and Renewable Energy (EERE) program under BMR award no. DE-EE0006852 . The structural characterization using NMR and PDF techniques was supported by the NorthEast Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center supported by the U.S. Department of Energy , Office of Science, Office of Basic Energy Sciences under award no. DE-SC0012583 . This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We thank Dr. Fengxia Xin for help with TG-MS data acquisition, and Drs. Jatinkumar Rana and Jia Ding, for many helpful discussions. Funding Information: This research was funded by U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE) program under BMR award no. DE-EE0006852. The structural characterization using NMR and PDF techniques was supported by the NorthEast Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under award no. DE-SC0012583. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We thank Dr. Fengxia Xin for help with TG-MS data acquisition, and Drs. Jatinkumar Rana and Jia Ding, for many helpful discussions. Publisher Copyright: © 2019 The AuthorsPeer reviewe

Ab initio structure search and in situ 7Li NMR studies of discharge products in the Li-S battery system.

The high theoretical gravimetric capacity of the Li-S battery system makes it an attractive candidate for numerous energy storage applications. In practice, cell performance is plagued by low practical capacity and poor cycling. In an effort to explore the mechanism of the discharge with the goal of better understanding performance, we examine the Li-S phase diagram using computational techniques and complement this with an in situ (7)Li NMR study of the cell during discharge. Both the computational and experimental studies are consistent with the suggestion that the only solid product formed in the cell is Li2S, formed soon after cell discharge is initiated. In situ NMR spectroscopy also allows the direct observation of soluble Li(+)-species during cell discharge; species that are known to be highly detrimental to capacity retention. We suggest that during the first discharge plateau, S is reduced to soluble polysulfide species concurrently with the formation of a solid component (Li2S) which forms near the beginning of the first plateau, in the cell configuration studied here. The NMR data suggest that the second plateau is defined by the reduction of the residual soluble species to solid product (Li2S). A ternary diagram is presented to rationalize the phases observed with NMR during the discharge pathway and provide thermodynamic underpinnings for the shape of the discharge profile as a function of cell composition.Fellowship support to KAS from the ConvEne IGERT Program of the National Science Foundation (DGE 0801627) is gratefully acknowledged. AJM acknowledges the support from the Winton Programme for the Physics of Sus-tainability. PDM and DSW thank the UK-EPSRC for financial support. This research made use of the shared experimental facilities of the Materials Research Laboratory (MRL), sup-ported by the MRSEC Program of the NSF under Award No. DMR 1121053. The MRL is a member of the NSF-funded Mate-rials Research Facilities Network (www.mrfn.org). CPG and ML thank the U.S. DOE Office of Vehicle Technologies (Con-tract No. DE-AC02-05CH11231) and the EU ERC (via an Ad-vanced Fellowship to CPG) for funding.This is the final published version. It first appeared at http://pubs.acs.org/doi/abs/10.1021/ja508982p

Multiple Redox Modes in the Reversible Lithiation of High-Capacity, Peierls-Distorted Vanadium Sulfide.

This is the author accepted manuscript. The final version is available from ACS via http://dx.doi.org/10.1021/jacs.5b03395Vanadium sulfide VS4 in the patronite mineral structure is a linear chain compound comprising vanadium atoms coordinated by disulfide anions [S2](2-). (51)V NMR shows that the material, despite having V formally in the d(1) configuration, is diamagnetic, suggesting potential dimerization through metal-metal bonding associated with a Peierls distortion of the linear chains. This is supported by density functional calculations, and is also consistent with the observed alternation in V-V distances of 2.8 and 3.2 Å along the chains. Partial lithiation results in reduction of the disulfide ions to sulfide S(2-), via an internal redox process whereby an electron from V(4+) is transferred to [S2](2-) resulting in oxidation of V(4+) to V(5+) and reduction of the [S2](2-) to S(2-) to form Li3VS4 containing tetrahedral [VS4](3-) anions. On further lithiation this is followed by reduction of the V(5+) in Li3VS4 to form Li3+xVS4 (x = 0.5-1), a mixed valent V(4+)/V(5+) compound. Eventually reduction to Li2S plus elemental V occurs. Despite the complex redox processes involving both the cation and the anion occurring in this material, the system is found to be partially reversible between 0 and 3 V. The unusual redox processes in this system are elucidated using a suite of short-range characterization tools including (51)V nuclear magnetic resonance spectroscopy (NMR), S K-edge X-ray absorption near edge spectroscopy (XANES), and pair distribution function (PDF) analysis of X-ray data.SB acknowledges Schlumberger Stichting Fund and European Research Council (EU ERC) for funding. JC thanks BK21 plus project of Korea. We thank Phoebe Allan and Andrew J. Morris, University of Cambridge, for useful discussions. We also thank Trudy Bolin and Tianpin Wu of Beamline 9-BM, Argonne National Laboratory for help with XANES measurements. The DFT calculations were performed at the UCSB Center for Scientific Computing at UC Santa Barbara, supported by the California Nanosystems Institute (NSF CNS-0960316), Hewlett-Packard, and the Materials Research Laboratory (DMR-1121053). This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357