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

Origin of Capacity Fading in Nano-Sized Co3O4Electrodes: Electrochemical Impedance Spectroscopy Study

Transition metal oxides have been suggested as innovative, high-energy electrode materials for lithium-ion batteries because their electrochemical conversion reactions can transfer two to six electrons. However, nano-sized transition metal oxides, especially Co3O4, exhibit drastic capacity decay during discharge/charge cycling, which hinders their practical use in lithium-ion batteries. Herein, we prepared nano-sized Co3O4with high crystallinity using a simple citrate-gel method and used electrochemical impedance spectroscopy method to examine the origin for the drastic capacity fading observed in the nano-sized Co3O4anode system. During cycling, AC impedance responses were collected at the first discharged state and at every subsequent tenth discharged state until the 100th cycle. By examining the separable relaxation time of each electrochemical reaction and the goodness-of-fit results, a direct relation between the charge transfer process and cycling performance was clearly observed

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

Chiral and steric effects in the efficient binding of α α α α-anomeric deoxyoligonucleoside N-alkylphosphoramidates to ssDNA and RNA

International audienceWe report hybridization properties of new phosphate-modified α α α α-oligonucleoside analogs with non-ionic or cationic internucleotide linkages such as methoxy-ethylphosphoramidate (PNHME), phosphoromorpholi-date (PMOR) and dimethylaminopropylphosphor-amidate (PNHDMAP). First we evaluated the chirality effect of the phosphorus atom on the affinity of α α α α-or β β β β-dodecanucleoside phosphodiesters containing one chirally enriched N-alkylphosphoramidate linkage located in the middle of the sequence d(TCTT-AA*CCCACA). As for P-substituted β β β β-oligonucleo-tides, a difference in binding behavior between the two diastereoisomers (difference in ∆ ∆ ∆ ∆T m) exists in the hybridization properties of α α α α-analogs when DNA was the target but this effect was not detrimental to duplex stability. This effect was considerably reduced when RNA was the target. Secondly we studied the effect of steric hindrance around phosphorus on the affinity of fully modified β β β β-and α α α α-oligo-nucleoside N-alkylphosphoramidates for their DNA and RNA targets. This effect was very weak with α α α α-analogs whereas it was more pronounced with β β β β-oligos. PNHME-modified α α α α-oligonucleosides formed more stable duplexes with DNA (∆ ∆ ∆ ∆T m +9.6°°°°C) and RNA (∆ ∆ ∆ ∆T m +1.4°°°°C) targets than the 'parent' phosphodiester. Finally, base pairing specificity of these α α α α-oligonucleo-side N-alkylphosphoramidates for their targets was found to be as high as for natural oligonucleoside phosphodiesters

Rechargeable Li₂O₂ electrode for lithium batteries

Rechargeable lithium batteries represent one of the most important developments in energy storage for 100 years, with the potential to address the key problem of global warming. However, their ability to store energy is limited by the quantity of lithium that may be removed from and reinserted into the positive intercalation electrode, LixCoO2, 0.5 &lt; x &lt; 1 (corresponding to 140 mA(.)h g(-1) of charge storage). Abandoning the intercalation electrode and allowing Li to react directly with O-2 from the air at a porous electrode increases the theoretical charge storage by a remarkable 5-10 times! Here we demonstrate two essential prerequisites for the successful operation of a rechargeable Li/O-2 battery; that the Li2O2 formed on discharging such an O-2 electrode is decomposed to Li and O-2 on charging (shown here by in situ mass spectrometry), with or without a catalyst, and that charge/discharge cycling is sustainable for many cycles.</p