2D exchange NMR spectra under slow MAS: A simplified scheme to obtain pure-phase spectra without unwanted cross peaks

Accessing the bottleneck in all-solid state batteries, lithium-ion transport over the solid-electrolyte-electrode interface

Solid-state batteries potentially offer increased lithium-ion battery energy density and safety as required for large-scale production of electrical vehicles. One of the key challenges toward high-performance solid-state batteries is the large impedance posed by the electrode–electrolyte interface. However, direct assessment of the lithium-ion transport across realistic electrode–electrolyte interfaces is tedious. Here we report two-dimensional lithium-ion exchange NMR accessing the spontaneous lithium-ion transport, providing insight on the influence of electrode preparation and battery cycling on the lithium-ion transport over the interface between an argyrodite solid-electrolyte and a sulfide electrode. Interfacial conductivity is shown to depend strongly on the preparation method and demonstrated to drop dramatically after a few electrochemical (dis)charge cycles due to both losses in interfacial contact and increased diffusional barriers. The reported exchange NMR facilitates non-invasive and selective measurement of lithium-ion interfacial transport, providing insight that can guide the electrolyte–electrode interface design for future all-solid-state batteries.

The large impedance at the interface between electrode and electrolyte poses a challenge to the development of solid-state batteries. Here the authors utilize two-dimensional lithium-ion exchange-NMR to monitor the spontaneous lithium-ion transport, providing insight into the interface design.

Adding a lens Improves spinning speed characterization

Highly stable sample rotation is important in many solid-state NMR experiments. Whether the necessary stability is achieved is not always clear. Typically only an average frequency over some time interval (often relatively long and unknown) is available from the spinning speed controller readout, which is not representative of the short-term variations of instantaneous rotation frequency. The necessity of the relatively slow measurement of spinning speed is a consequence of phase noise in the tachometer, which prevents speed measurement to be both rapid and precise at the same time. We show that adding a lens to the tachometer, without any other changes in the probe, reduces phase noise by nearly an order of magnitude and allows improved measurement of the spinning speed.

Pf1 bacteriophage hydration by magic angle spinning solid-state NMR

High resolution two- and three-dimensional heteronuclear correlation spectroscopy ((1)H-(13)C, (1)H-(15)N, and (1)H-(13)C-(13)C HETCOR) has provided a detailed characterization of the internal and external hydration water of the Pf1 virion. This long and slender virion (2000 nm × 7 nm) contains highly stretched DNA within a capsid of small protein subunits, each only 46 amino acid residues. HETCOR cross-peaks have been unambiguously assigned to 25 amino acids, including most external residues 1-21 as well as residues 39-40 and 43-46 deep inside the virion. In addition, the deoxyribose rings of the DNA near the virion axis are in contact with water. The sets of cross-peaks to the DNA and to all 25 amino acid residues were from the same hydration water (1)H resonance; some of the assigned residues do not have exchangeable side-chain protons. A mapping of the contacts onto structural models indicates the presence of water "tunnels" through a highly hydrophobic region of the capsid. The present results significantly extend and modify results from a lower resolution study, and yield a comprehensive hydration surface map of Pf1. In addition, the internal water could be distinguished from external hydration water by means of paramagnetic relaxation enhancement. The internal water population may serve as a conveniently localized magnetization reservoir for structural studies.

Li-ion diffusion in the equilibrium nanomorphology of spinel Li(4+x)Ti(5)O(12)

Li(4)Ti(5)O(12) spinel as Li-ion electrode material combines good capacity, excellent cycleability with a high rate capability. Although the potential of about 1.56 V vs Li is relatively high, these features make it the anode of choice for state of the art high power Li-ion batteries. Although the flat voltage profile reflects a two-phase reaction during lithiation, the small change in lattice parameters upon lithiation ("zero-strain" property) leads to a solid solution in equilibrium, as recently demonstrated with diffraction. In this study, the morphology and Li-ion mobility is studied by NMR spectroscopy leading to a more detailed picture, showing that the solid solution in Li(4+x)Ti(5)O(12) spinel should actually be described as domains with sizes less than 9 nm having either tetrahedral (8a) Li occupation or octahedral (16c) Li occupation. The abundant domain boundaries and the associated disorder appear to be responsible for the facile diffusion through the lattice, and hence these nm-sized domains are most likely the origin of the relative high rate capability of this material as electrode for Li-ion batteries. The small domain size, smaller than typical Debye lengths, makes that the material electrochemically behaves as a solid solution. As such, the results give insight in the fundamental properties of the "zero-strain" Li(4)Ti(5)O(12) spinel material explaining the favorable Li-ion battery electrode properties on an atomic level.

13C and 2H NMR Study of Structure and Dynamics in Banana B2 Phase of a Bent-Core Mesogen

In this paper, the difficulty in orienting the B(2) phase of the banana mesogen 1,3-Phenylene-bis 4-[4-(10-undecenyloxy)-benzoyloxy] benzoate (Pbis11BB) in a relatively high magnetic field is reported based on some observations using both (13)C and (2)H NMR. (2)H NMR spectra recorded for the two labeled isotopomers of Pbis11BB in the isotropic and B(2) phases are shown here. Preliminary results on the deuteron spin-spin relaxation (T(2)) data are reported at 61 MHz in order to underline the peculiar slow dynamics of banana-shaped liquid crystals (BLC), and these results are discussed in the framework of recent studies on similar BLC. The molecular structure and dynamics in the B(2) and crystalline phases are also studied by (13)C solid-state NMR techniques. The results also point to the slow dynamics in the B(2) phase of Pbis11BB. In particular, two-dimensional MAS exchange experiment has been performed to shed light on the molecular conformation structure of the five-ring banana core in the crystalline phase of Pbis11BB, and to compare with that of quantum mechanical calculations reported in the literature.

Biomolecular solid state NMR: advances in structural methodology and applications to peptide and protein fibrils

Solid state nuclear magnetic resonance (NMR) methods can provide atomic-level structural constraints on peptides and proteins in forms that are not amenable to characterization by other high-resolution structural techniques, owing to insolubility, high molecular weight, noncrystallinity, or other characteristics. Important examples include peptide and protein fibrils and membrane-bound peptides and proteins. Recent advances in solid state NMR methodology aimed at structural problems in biological systems are reviewed. The power of these methods is illustrated by experimental results on amyloid fibrils and other protein fibrils.

Lithium dynamics in LiMn2O4 probed directly by two-dimensional (7)Li NMR

LiMn2O4 has been studied using magic-angle-spinning nuclear magnetic resonance (MAS NMR). 1D MAS NMR shows three Li resonances assigned to different crystallographic sites. At low temperatures an extra peak appears, indicating charge ordering of Mn3+ and Mn4+. Direct observation of the lithium dynamics was possible using rotor-synchronized 2D exchange NMR. A millisecond time scale exchange of lithium starts around 285 K between the 8a and the 16c site. At 380 K lithium even starts to hop between more than two sites. The activation energies and Li jump rates are derived and are in agreement with those determined macroscopically.

INADEQUATE-CR experiments in the solid state

Through-bond connectivity can be probed by J couplings. For effective two-spin systems, the INADEQUATE experiment is highly valuable in liquid-state spectroscopy. It is the purpose of this Communication to show that in-phase INADEQUATE-CR spectra, where the intensity is concentrated in only one line of the J splitted doublet, can be obtained from solid-state samples. The problem of the cancellation of nonresolved multiplet lines, as experienced typically in INADEQUATE spectra in the solid, is resolved and the (13)C spectra become simpler because the number of resonance lines is reduced. Furthermore, a gain in signal intensity by 2 can, theoretically, be achieved. We limit the discussion to two-spin systems. In the present context, a two-spin system is defined considering the J coupling only. When the dipolar coupling is also taken into account, the two-spin system will usually become a many-spin system, but in the present context this is not relevant.