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

Critical size of a nano SnO2 electrode for Li-secondary battery

SnO2 nanoparticles with different sizes of ???3, ???4, and ???8 nm were synthesized using a hydrothermal method at 110, 150, and 200??C, respectively. The results showed that the ???3 nm-sized SnO 2 nanoparticles had a superior capacity and cycling stability as compared to the ???4 and ???8 nm-sized ones. The ???3 nm-sized nanoparticles exhibited an initial capacity of 740 mAh/g with negligible capacity fading. The electrochemical properties of these nanoparticles were superior to those of thin-film analogues. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed that the ???3 nm-sized SnO2 nanoparticles after electrochemical tests did not aggregate into larger Sn clusters, in contrast to those observed with the ???4 and ???8 nm-sized ones.close25724

Quantitative study of the short range order in B2O3 and B2S3 by MAS and two-dimensional triple-quantum MAS B-11 NMR

Two-dimensional multiple-quantum magic angle spinning (MQMAS) NMR and MAS NMR of B-11 at various magnetic fields, were applied to elucidate the structure of vitreous (glassy) boron trioxide (v-B2O3), vitreous boron trisulfide (v-B2S3) and crystalline boron trisulfide (c-B2S3). These techniques, when combined with computer simulations of the resulting spectra, provide the isotropic chemical shifts and the quadrupole parameters, as well as a quantitative measure of the intensities of various boron resonances. The MAS NMR of v-B2O3 produced overlapping anisotropic lineshapes corresponding to the -1/2 1/2 transition in two distinct types of BO3 units with 3(+/-0.08):1 intensity ratio. A combination of MAS and the multiple-quantum method resulted in a better resolved, isotropic B-11 spectrum of v-B2O3. A remarkable enhancement of resolution of the MQMAS NMR proved instrumental in finding and identifying various impurities present in V-B2S3 and c-B2S3. In addition to the resonances from boron in two types of BS, groups, four other structural units, BOS,, BO2S, BO3 and BS4, were elucidated from the spectra of vitreous and crystalline samples. The effects of various experimental parameters, such as the magnitude of the B-0 and B-1 fields, on the resolution of the MAS and MQMAS techniques are also shown.close585

Structural Study of xNa2S + (1 − x)B2S3 Glasses and Polycrystals by Multiple-Quantum MAS NMR of 11B and 23Na

Glasses and polycrystals in the series xNa2S + (1 − x)B2S3 have been prepared and studied by magic angle spinning (MAS) NMR and by two-dimensional multiple-quantum (MQ) MAS NMR of11B and 23Na. These techniques, when applied at various magnetic fields and combined with computer simulations of the spectra, provide new insights into the structure of the polycrystalline samples. Isotropic chemical shifts, quadrupolar parameters, and relative concentrations of the various boron sites are obtained by NMR and correlated with the known structures of boron trisulfide (x = 0), sodium metathioborate (x = 0.5) and sodium orthothioborate (x = 0.75). A structural model of polycrystalline sodium dithioborate (x = 0.33) is proposed. The MQMAS NMR method significantly enhanced the resolution in 11B spectra of xNa2S + (1 − x)B2S3 glasses and proved instrumental in finding and identifying various structural units present within these materials as the modification of the B2S3network progressed with increasing Na2S content. The dominant 11B resonances observed in the glassy samples represent the same basic structural units that were observed in the polycrystalline compounds. In addition, several new resonances featuring trigonally and tetrahedrally coordinated boron atoms in various transitional structures between dithioborate and metathioborate, or between metathioborate and orthothioborate, were found. 23Na NMR proved less informative, especially in the glassy samples where the motion of the sodium ions between various sites precluded the observation of well-resolved spectra.Reprinted with permission from Journal of the American Chemical Society 120 (1998): 7337–7346, doi:10.1021/ja9800481. Copyright 1998 American Chemical Society.</p

Structural study of xNa(2)S+(1-x)B2S3 glasses and polycrystals by multiple-quantum MAS NMR of B-11 and Na-23

Glasses and polycrystals in the series xNa(2)S + (1 - x)B2S3 have been prepared and studied by magic angle spinning (MAS) NMR and by two-dimensional multiple-quantum (MQ) MAS NMR of B-11 and Na-23. These techniques, when applied at various magnetic fields and combined with computer simulations of the spectra, provide new insights into the structure of the polycrystalline samples. Isotropic chemical shifts, quadrupolar parameters, and relative concentrations of the various boron sites are obtained by NMR and correlated with the known structures of boron trisulfide (x = 0), sodium metathioborate (x = 0.5) and sodium orthothioborate (x = 0.75). A structural model of polycrystalline sodium dithioborate (x = 0.33) is proposed. The MQMAS NMR method significantly enhanced the resolution in B-11 spectra of xNa(2)S + (1 - x)B2S3 glasses and proved instrumental in finding and identifying various structural units present within these materials as the modification of the B2S3 network progressed with increasing Na2S content. The dominant B-11 resonances observed in the glassy samples represent the same basic structural units that were observed in the polycrystalline compounds. In addition, several new resonances featuring trigonally and tetrahedrally coordinated boron atoms in various transitional structures between dithioborate and metathioborate, or between metathioborate and orthothioborate, were found. Na-23 NMR proved less informative, especially in the glassy samples where the motion of the sodium ions between various sites precluded the observation of well-resolved spectra.close363

MoS2 Nanoplates Consisting of Disordered Graphene-like Layers for High Rate Lithium Battery Anode Materials

MoS2 nanoplates, consisting of disordered graphene-like layers, with a thickness of similar to 30 nm were prepared by a simple, scalable, one-pot reaction using Mo(CO)(6) and S in an autoclave. The product has a interlayer distance of 0.69 nm, which is much larger than its bulk counterpart (0.62 nm). This expanded interlater distance and disordered graphene-like morphology led to an excellent rate capability even at a 50C (53.1 A/g) rate, showing a reversible capacity of 700 mAh/g. In addition, a full cell (LiCoO2/MoS2) test result also demonstrates excellent capacity retention up to 60 cycles.close16211

Catalytic Role of Ge in Highly Reversible GeO2/Ge/C Nanocomposite Anode Material for Lithium Batteries

GeO2/Ge/C anode material synthesized using a simple method involving simultaneous carbon coating and reduction by acetylene gas is composed of nanosized GeO2/Ge particles coated by a thin layer of carbon, which is also interconnected between neighboring particles to form clusters of up to 30 mu m. The GeO2/Ge/C composite shows a high capacity of up to 1860 mAh/g and 1680 mAh/g at 1 C (2.1 A/g) and 10 C rates, respectively. This good electrochemical performance is related to the fact that the elemental germanium nanoparticles present in the composite increases the reversibility of the conversion reaction of GeO2. These factors have been found through investigating and comparing GeO2/Ge/C, GeO2/C, nanosized GeO2, and bulk GeO2.close2

Magnesium(II) bis(trifluoromethane sulfonyl) imide-based electrolytes with wide electrochemical windows for rechargeable magnesium batteries

We present a promising electrolyte candidate, Mg(TFSI)2 dissolved in glyme/diglyme, for future design of advanced magnesium (Mg) batteries. This electrolyte shows high anodic stability on an aluminum current collector and allows Mg stripping at the Mg electrode and Mg deposition on the stainless steel or the copper electrode. It is clearly shown that nondendritic and agglomerated Mg secondary particles composed of ca. 50 nm primary particles alleviating safety concern are formed in glyme/diglyme with 0.3 M Mg(TFSI) 2 at a high rate of 1C. Moreover, a Mg(TFSI)2-based electrolyte presents the compatibility toward a Chevrel phase Mo 6S8, a radical polymer charged up to a high voltage of 3.4 V versus Mg/Mg2+ and a carbon-sulfur composite as cathodes.close6