Novel selective 1D experiments based on heteronuclearJ cross-polarization

Parella, Teodor; Belloc, Jordi; Sánchez‐Ferrando, Francisco; Virgili, Albert

doi:10.1002/(sici)1097-458x(199909)37:9<631::aid-mrc512>3.0.co;2-0

Cited by 13 publications

(40 citation statements)

References 36 publications

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“…Spectra were calibrated on the solvent signals. 13 C-edited 1 H NMR spectra, 17 DEPT spectra, 18 and 13 C NMR spectra obtained using the gated 1 H-decoupling technique 19 were used to assist in signal assignment. GC-MS analyses were conducted on a Saturno 2.200 instrument from Varian and a CP-SIL8 column 30 m long ϫ 25 mm inner diameter ͑i.d.͒.…”

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confidence: 99%

Oxygen Lattice Instability as a Capacity Fading Mechanism for 5 V Cathode Materials

Caballero

Hernán

Melero

et al. 2005

J. Electrochem. Soc.

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The origin of the overcharge in the 5 V region observed in lithium-substituted LiM x Mn 2Ϫx O 4ϩ␦ spinels (M ϭ Cr, Ni, Cu; x Ϸ 0.2) prepared at 500°C was analyzed by using accurate analytical spectroscopic techniques ͑mass spectroscopy, nuclear magnetic resonance͒ to examine the electrolyte behavior. The spectra revealed organic solvents to be stable as no decomposition products were detected, thus excluding the electrolyte oxidation as a side reaction accounting for the cell overcharge. However, these spinels contain excess oxygen in an amount that was quantified from thermogravimetric data. The excess oxygen plays a prominent role in the electrochemical response of the spinel. The cyclic voltammetry and galvanostatic results support the assumption that the excess oxygen can be released above 4.5 V. The additional capacity obtained and that required to release the oxygen were quite consistent. This must be the origin of both the overcharge and the poor performance of the cells compared with spinels of similar composition but synthesized at higher temperatures ͑800°C͒, the excess of oxygen in which was smaller. The ability of some Li-Mn based spinels to exhibit high-voltage plateaus at about 5 V has opened up new prospects for lithium batteries such as the possibility of manufacturing high-voltage batteries capable of supplying highly specific energy.1 LiM to Mn 5ϩ or Mn 6ϩ hypothesized for the undoped spinel has not yet been confirmed. Two alternative side reactions can be considered: ͑i͒ electrolyte oxidation above 4.6 V and (ii) a redox process undergone by the oxygen lattice of the spinel framework involving release of oxygen. This latter model can be related with theoretical computations based on either first-principles calculations 10 or the DV-X␣ molecular orbital model.11 Based on such models, when M is substituted by Mn ions, a new O 2p band at a low energy is responsible for the high electrochemical cell voltage observed. Simultaneously, evolved oxygen may oxidize organic solvents. These unwanted side reactions can lead to a premature cell capacity loss. Three recent reports 12-14 have insisted on the origin of the electrochemical activity above 4.5 V. Thus, Wang et al. 12 claim that the high voltage capacity of Li 1ϩx Mn 2Ϫx O 4Ϯz originates from the extraction of Li ϩ at 16d sites, whereas Shin and Manthiram 13,14 ascribe it to the involvement of O 2Ϫ -2p in the redox process. The aim of this work was to help clarify the processes taking place in the high-potential region of 5 V in cation-substituted lithium manganese spinels. For this purpose, Cr-, Ni-, and Cusubstituted spinels containing the doping elements in various oxidation states and prepared at two different temperatures ͑500 and 800°C͒ were examined. The electrolyte decomposition was analyzed using mass spectrometry ͑MS͒ and nuclear magnetic resonance ͑NMR͒ measurements. These measurements, together with thermogravimetric ͑TG͒ data, confirmed the central role played by the excess oxygen ion in the spinel lattice. ExperimentalThree series ...

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confidence: 99%

Oxygen Lattice Instability as a Capacity Fading Mechanism for 5 V Cathode Materials

Caballero

Hernán

Melero

et al. 2005

J. Electrochem. Soc.

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“…Finally, we inserted the a ‐DENA sequence element in the ‘edited’ version of the HSQC and found that it causes no particular difficulties. The reconstruction is quite satisfactory as Fig.…”

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confidence: 99%

Reconstruction of full high‐resolution HSQC using signal split in aliased spectra

Foroozandeh

Jeannerat

2015

Magnetic Reson in Chemistry

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Resolution enhancement is a long-sought goal in NMR spectroscopy. In conventional multidimensional NMR experiments, such as the (1) H-(13) C HSQC, the resolution in the indirect dimensions is typically 100 times lower as in 1D spectra because it is limited by the experimental time. Reducing the spectral window can significantly increase the resolution but at the cost of ambiguities in frequencies as a result of spectral aliasing. Fortunately, this information is not completely lost and can be retrieved using methods in which chemical shifts are encoded in the aliased spectra and decoded after processing to reconstruct high-resolution (1) H-(13) C HSQC spectrum with full spectral width and a resolution similar to that of 1D spectra. We applied a new reconstruction method, RHUMBA (reconstruction of high-resolution using multiplet built on aliased spectra), to spectra obtained from the differential evolution for non-ambiguous aliasing-HSQC and the new AMNA (additional modulation for non-ambiguous aliasing)-HSQC experiments. The reconstructed spectra significantly facilitate both manual and automated spectral analyses and structure elucidation based on heteronuclear 2D experiments. The resolution is enhanced by two orders of magnitudes without the usual complications due to spectral aliasing.

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“…The possibility to obtain separately in-phase or antiphase proton magnetization (with respect to the 1 J(CH) coupling constant) from 1D carbon-selective HCP experiments was already pointed out simply by proper choice of some 90°proton and carbon pulses embedding the HCP block [16]. Based on this idea, attention has been focused on the study of the different coherence transfer mechanisms involved during the HCP mixing processes.…”

Section: Resultsmentioning

confidence: 99%

“…Among others, specific NMR pulse sequences making use of 1 H-X HCP [11,12] have been described for small molecules at natural abundance (X ¼ 13 C) [13][14][15][16], for large and isotopically labelled biomolecules (X ¼ 13 C and 15 N) [17][18][19][20], and also successfully applied to other heteronuclei such as 31 P [21,22] or 113 Cd [23,24].…”

Section: Introductionmentioning

confidence: 99%

Novel selective 1D experiments based on heteronuclearJ cross-polarization

Cited by 13 publications

References 36 publications

Oxygen Lattice Instability as a Capacity Fading Mechanism for 5 V Cathode Materials

Oxygen Lattice Instability as a Capacity Fading Mechanism for 5 V Cathode Materials

Reconstruction of full high‐resolution HSQC using signal split in aliased spectra

Spin-state-selective excitation in gradient-selected heteronuclear cross-polarization NMR experiments

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