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

Room-Temperature synthesis leading to nanocrystalline Ag2V 4O11

This work highlights a roomerature composition study of the Ag 2O/V2O5/HF(aq) ternary system, leading to the precipitation of either various silver vanadates having Ag/V ratios from 1/2 to 3/1 or the new silver vanadium oxyfluoride compounds Ag 4V2O6F2 and Ag3VO 2F4, and a synthetic procedure that affords nanocrystalline Ag2V4O11 (SVO) at room temperature. The as-precipitated SVO particles exhibit an acicular morphology, 10-15 - 50-200 nm in size, and present a peculiar reactivity vs lithium notably through a Ag+/Li+ displacement reaction that progresses in a reversible fashion. This step forward thus enables the reversible and simultaneous combination of two active redox processes (silver and vanadium), providing a significant enhancement in the cathode gravimetric capacity of 320 mAh/g at C rate and more than 250 mAh/g at 5C. © 2010 American Chemical Society

Ag 6Mo 2O 7F 3Cl: A new silver cathode material for enhanced ICD primary lithium batteries

As a potential cathode material for the ICD lithium battery, one advantage of Ag 6Mo 2O 7F 3Cl (SMOFC) Is its enhanced gravimetric capacity of ca. 133 mAh/g above 3 V (vs Li +/Li) delivered by two biphasic transitions at 3.46 and 3.39 V (vs Li +/Li). The unique crystal structure of SMOFC enables a high sliver ion conduction: σ ⊥[001] = 3.10 -2 S/cm (±2.10 -2 S/cm) and σ// [001] = 4.10 -3 S/cm (±2.10 -3 S/cm) and, hence, an excellent discharge rate capability. Lithium insertion has been monitored by in situ XRD measurements with HRTEM investigations. There is a linear isotropic collapse of the structure leading to a fully amorphous structure beyond four Inserted lithiums. © 2010 American Chemical Society

Room temperature synthesis of the larger power, high silver density cathode material Ag 4V 2O 6F 2 for implantable cardioverter defibrillators

New cathode materials will lead to technological advances for implantable cardioverter defibrillators, ICDs, such as reduced size and increased performance of the device. While the industry standard silver vanadium oxide Ag 2V 4On 11 exhibits great chemical/ electrochemical stability, dense silver oxide fluoride materials are advantageous because of high crystal density that can result in an increased capacity above 3 V. This report highlights the reactivity at room temperature between Ag 2O and V 2O 5 in an aqueous HF solution which affords a rapid precipitation of sub-micrometer sized Ag 4V 2O 6F 2 (SVOF), a high capacity Li-battery cathode material. This system opens new and novel synthetic strategies in the design of new oxide fluoride materials. © 2009 American Chemical Society

Structural and transport evolution in the Li_xAg₂V₄O₁₁ system

We investigated the effect of inserting lithium into Ag2V4O11 (ε-SVO) on the structure, electronic properties and redox committed by combining in situ XRD measurements, ESR spectroscopy and 4 probes DC conductivity coupled with thermopower measurements. The electrochemical discharge occurs in three consecutive steps above 2 V (vs. Li+/Li). The first one, between 0 x-SVO, has been ascribed to the V5+ reduction through a solid solution mechanism. This reduction competes with a Li+/Ag+ displacement reaction which leads to a structural collapse owing to the ionic radii mismatch between the withdrawn Ag+ and the inserted Li+. The silver reduction progresses continuously with two different slopes along two composition–potential plateaus at 2.81 V and 2.55 V. Finally, the reduction continues until we obtain an amorphous structure with V4+ and a ε of V3+. Although, the silver re-enters the structure during the subsequent recharge, the original structure is not recovered. The reduction of silver forming silver metal nano-clusters acts to increase the electronic conductivity from 3.8 × 10−5 S cm−1 to 1.4 × 10−3 S cm−1. In complement to this study, we also report on a low temperature hydro-(solvo)-thermal approach using HF(aq) as a mineralizer, which enables the synthesis of nano-sized ε-SVO particles that exhibit superior electrochemical performances compared to conventional particles synthesized by solid-state reaction

Magnetic properties of spinel-type oxides NiMn2-xMexO4

New materials, based on the well-known spinel compound NiMn2O4, have been synthesized and characterized from the magnetic point of view. The manganese cation was partially substituted in the general formula NiMn2-xMexO4 , by nonmagnetic and magnetic elements, such as Me = Ga, Zn, Ni and Cr (0 x 1). Prior to the determination of their magnetic properties, the non-substituted spinel NiMn2O4 was carefully characterized and studied as a function of the oxygen stoichiometry, based on the influence of the annealing atmosphere and quenching rate. The ferrimagnetic character was observed in all samples, with a paramagnetic-to-ferromagnetic transition temperature Tc stabilized at 110 K, and well defined long-range antiferromagnetic interactions at lower temperatures, which depend on the applied field and the substitute concentrationAuthors from Chile and O.P. thank projects Fondecyt-Chile 1020066, 7020066 and 1050178. Authors from France and Brazil thank project CAPES/COFECUB 416/03. Authors from France thank Région Bretagne for financial supportPeer reviewe

Copper extrusion/reinjection in Cu-based thiospinels by electrochemical and chemical routes

The electrochemical reactivity of CuTi 2S 4 and CuCr 2S 1 spinel samples toward Li was studied over a wide range of voltages. Their electrochemical behavior can be decomposed into two steps. For less than two inserted lithium, we emphasized a Li-driven electrochemical displacement reaction that led to the extrusion of copper from lithium, leading to the rocksalt-type structure phases Li 2Ti 2S 4 and Li 2-xCu 0.3Cr 2S 4, whereas conversion reactions were observed beyond x = 2. These conversion reactions were shown to have a large rechargeable uptake and release of Li + ions (7 per formula unit) that rapidly fade on cycling. Regarding the Cu extrusion, we demonstrated that this process is reversible for the Ti-based spinel upon oxidation through a chemically assisted electrochemical process. For the Cr-based system, a new phase LiCu 0.7Cr 2S 4 was evidenced to form on oxidation. This difference is explained in terms of band structure considerations and d-sp redox chemistry. Chemical reinjection of Cu into TizS4 forming the single phase Cu xTi 2S 4 (0 < x < 1) from the reaction of Ti 2S 4 powders with an aqueous CuSO 4· nH 2O solution is also reported. It is shown that traces of H 2S coming from the slight chemical instability of Ti 2S 4 in water are necessary for initiating the chemical reinjection reaction to form Cu xTi 2S 4. © 2006 American Chemical Society

Ag4V2O6F2 (SVOF): A high silver density phase and potential new cathode material for implantable cardioverter defibrillators

The electrochemical reactivity of the cathode material Ag4V 2O6F2 (SVOF) versus lithium, with a particular emphasis on the lithium insertion mechanism, was studied by means of the complementary techniques in situ X-ray diffraction, electron paramagnetic resonance, and high-resolution transmisssion electron microscopy. This study confirms the initial reports of a high capacity for SVOF of 148 mAh/g above 3 V and that the reduction of silver above 3 V (vs Li+/Li0) leads to a loss of SVOF crystallinity until it becomes completely amorphous between the third and fourth lithiums inserted. Next, vanadium is reduced between 2.5 and 1.5 V (vs Li+/Li0) for the fifth and sixth lithiums inserted. In addition, the polarization within the cathode is significantly lower for the vanadium reduction than for the silver reduction. The silver metal morphologies consisted of nanoparticles (∼5 nm diameter) and dendrites and were both seen in samples of lithiated SVOF. © 2008 American Chemical Society

Recent developments in transmission electron microscopy techniques to the characterization of cycled Li-ion electrode materials

Battery performance depends on many factors amongst which the selection of the appropriate electrode material and the control of the electrode/electrolyte interface upon cycling. In order to address these issues, electrochemists have to design new electrode materials, and 'enter the private life' of a battery. Transmission Electron Microscopy (TEM) is a powerful tool to help scientists to characterize each part of the device. Recent developments in TEM techniques have been proposed and developed, through the Alistore Electron Microscopy platform (AEMP), to allow the observation of Li-ion air sensitive electrode materials. Our team is now going one step further by using High Resolution Electron Energy Loss Spectroscopy (HREELS) and nanoprobe EDS as well as other TEM techniques exhibiting the advantage of high lateral resolution for chemical analysis and for structural determination (by means of electron diffraction and high-resolution imaging). The AEMP holds at the same time the equipment and the skills to run such experiments copyright The Electrochemical Society