In Situ Ambient Pressure X-ray Photoelectron Spectroscopy Studies of Lithium-Oxygen Redox Reactions

The lack of fundamental understanding of the oxygen reduction and oxygen evolution in nonaqueous electrolytes significantly hinders the development of rechargeable lithium-air batteries. Here we employ a solid-state Li4+xTi5O12/LiPON/LixV2O5 cell and examine in situ the chemistry of Li-O2 reaction products on LixV2O5 as a function of applied voltage under ultra high vacuum (UHV) and at 500 mtorr of oxygen pressure using ambient pressure X-ray photoelectron spectroscopy (APXPS). Under UHV, lithium intercalated into LixV2O5 while molecular oxygen was reduced to form lithium peroxide on LixV2O5 in the presence of oxygen upon discharge. Interestingly, the oxidation of Li2O2 began at much lower overpotentials (~240 mV) than the charge overpotentials of conventional Li-O2 cells with aprotic electrolytes (~1000 mV). Our study provides the first evidence of reversible lithium peroxide formation and decomposition in situ on an oxide surface using a solid-state cell, and new insights into the reaction mechanism of Li-O2 chemistry.National Science Foundation (U.S.) (Materials Research Science and Engineering Center (MRSEC) Program, Award DMR-0819762)United States. Dept. of Energy (Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies of the U. S. Department of Energy under contract no. DE-AC03-76SF00098)Lawrence Berkeley National LaboratoryUnited States. Dept. of Energy (Office of Basic Energy Sciences, Materials Sciences and Engineering

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

From Anionic to Cationic Alpha-Oligodeoxynucleosides

International audienc

From Anionic to Cationic Alpha-Oligodeoxynucleosides

International audienc

Efficient release of base-sensitive oligonucleotides from solid supports using fluoride ions.

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A base labile group for 2'-OH protection of ribonucleosides : as a major challenge for RNA synthesis.

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