Materials’ Methods: NMR in Battery Research

Improving electrochemical energy storage is one of the major issues of our time. The search for new battery materials together with the drive to improve performance and lower cost of existing and new batteries is not without its challenges. Success in these matters is undoubtedly based on first understanding the underlying chemistries of the materials and the relations between the components involved. A combined application of experimental and theoretical techniques has proven to be a powerful strategy to gain insights into many of the questions that arise from the “how do batteries work and why do they fail” challenge. In this Review, we highlight the application of solid-state nuclear magnetic resonance (NMR) spectroscopy in battery research: a technique that can be extremely powerful in characterizing local structures in battery materials, even in highly disordered systems. An introduction on electrochemical energy storage illustrates the research aims and prospective approaches to reach these. We particularly address “NMR in battery research” by giving a brief introduction to electrochemical techniques and applications as well as background information on both in and ex situ solid-state NMR spectroscopy. We will try to answer the question “Is NMR suitable and how can it help me to solve my problem?” by shortly reviewing some of our recent research on electrodes, microstructure formation, electrolytes and interfaces, in which the application of NMR was helpful. Finally, we share hands-on experience directly from the lab bench to answer the fundamental question “Where and how should I start?” to help guide a researcher’s way through the manifold possible approaches.This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 655444 (O.P.). K.J.G. thanks the Winston Churchill Foundation of the United States and the Herchel Smith Scholarship for financial support

Structural Stability from Crystallographic Shear in TiO2_2-Nb2_2O5_5 Phases: Cation Ordering and Lithiation Behavior of TiNb24_{24}O62_{62}

The host structure and reversible lithium insertion and extraction of an intercalation compound, TiNb$_{24}$O$_{62}$, are described. Neutron diffraction, applied for the first time to TiNb$_{24}$O$_{62}$, allowed an accurate refinement of the complex block superstructure, particularly with respect to the oxygen sublattice. Analysis of the transition-metal sites revealed significant cation ordering in the mixed-metal oxide. Electrochemical analysis demonstrated highly reversible lithium intercalation with ca. 190 mA·h·g$^{-1}$) after 100 cycles ($C$/10 rate, 3 months). The effect of the potential window on the capacity, polarization, and reversibility was carefully examined; a minimum voltage limit of 1.1-1.2 V is critical for efficient and reversible cycling. The galvanostatic intermittent titration technique revealed three solid-solution regions, with different lithium diffusivities, in addition to the two-phase plateau that was clearly observed in the $V$ versus $Q$ discharge/charge profile. Lithium-ion diffusion decreases by over 3 orders of magnitude from the dilute lithium limit early in the discharge to the lithium-stuffed phase Li$_{37.5(1.0)}$TiNb$_{24}$O$_{62}$. Nevertheless, prior to lithium stuffing, TiNb$_{24}$O$_{62}$ possesses intrinsically rapid lithium-ion kinetics, as demonstrated by the high-rate performance in thick films of ca. 10 μm particles when interfaced with a carbon-coated aluminum foil substrate. The TiO$_2$·Nb$_2$O$_5$ phase diagram is examined and electrochemical results are compared to related superstructures of crystallographically sheared blocks of octahedra in the TiO$_2$·Nb$_2$O$_5$ homologous series including the H-Nb$_2$O$_5$ end member.The authors gratefully acknowledge financial support provided by FRM II to perform the neutron scattering measurements at the MLZ, Garching, Germany. K.J.G. thanks the Winston Churchill Foundation of the United States and the Herchel Smith Scholarship for funding

Enhanced efficiency of solid-state NMR investigations of energy materials using an external automatic tuning/matching (eATM) robot.

We have developed and explored an external automatic tuning/matching (eATM) robot that can be attached to commercial and/or home-built magic angle spinning (MAS) or static nuclear magnetic resonance (NMR) probeheads. Complete synchronization and automation with Bruker and Tecmag spectrometers is ensured via transistor-transistor-logic (TTL) signals. The eATM robot enables an automated "on-the-fly" re-calibration of the radio frequency (rf) carrier frequency, which is beneficial whenever tuning/matching of the resonance circuit is required, e.g. variable temperature (VT) NMR, spin-echo mapping (variable offset cumulative spectroscopy, VOCS) and/or in situ NMR experiments of batteries. This allows a significant increase in efficiency for NMR experiments outside regular working hours (e.g. overnight) and, furthermore, enables measurements of quadrupolar nuclei which would not be possible in reasonable timeframes due to excessively large spectral widths. Additionally, different tuning/matching capacitor (and/or coil) settings for desired frequencies (e.g. $^{7}$Li and $^{31}$P at 117 and 122MHz, respectively, at 7.05 T) can be saved and made directly accessible before automatic tuning/matching, thus enabling automated measurements of multiple nuclei for one sample with no manual adjustment required by the user. We have applied this new eATM approach in static and MAS spin-echo mapping NMR experiments in different magnetic fields on four energy storage materials, namely: (1) paramagnetic $^{7}$Li and $^{31}$P MAS NMR (without manual recalibration) of the Li-ion battery cathode material LiFePO$_{4}$; (2) paramagnetic $^{17}$O VT-NMR of the solid oxide fuel cell cathode material La$_{2}$NiO$_{4+δ}$; (3) broadband $^{93}$Nb static NMR of the Li-ion battery material BNb$_{2}$O$_{5}$; and (4) broadband static $^{127}$I NMR of a potential Li-air battery product LiIO$_{3}$. In each case, insight into local atomic structure and dynamics arises primarily from the highly broadened (1-25MHz) NMR lineshapes that the eATM robot is uniquely suited to collect. These new developments in automation of NMR experiments are likely to advance the application of in and ex situ NMR investigations to an ever-increasing range of energy storage materials and systems.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 655444 (O.P.). D.M.H. acknowledges funding from the Cambridge Commonwealth Trusts. J.L. gratefully acknowledges Trinity College, Cambridge (UK) for funding. K.J.G. gratefully acknowledges funding from the Winston Churchill Foundation of the United States and the Herchel Smith Scholarship. M.B. is the CEO of NMR Service GmbH (Erfurt, Germany), which manufactures the eATM device; M.B. acknowledges funding of the Central Innovation Programme for small and medium-sized enterprises (SMEs; Zentrales Innovationsprogramm Mittelstand, ZIM) of the German Federal Ministry of Economic Affairs and Energy (Bundesministerium für Wirtschaft und Energie, BMWi) under the Grant No. KF 2845501UWF. DFT calculations were performed on (1) the Darwin Supercomputer of the University of Cambridge High Performance Computing Service (http://www.hpc.cam.ac.uk), provided by Dell Inc. using Strategic Research Infrastructure Funding from the Higher Education Funding Council for England and funding from the Science and Technology Facilities Council and (2) the Center for Functional Nanomaterials cluster, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886

Energy storage mechanisms in vacancy-ordered Wadsley-Roth layered niobates

Wadsley–Roth (WR) crystallographic shear structures demonstrate high energy and power densities as Li-ion battery anode materials. We report the (de)lithiation behavior of two WR-derived layered niobates: NaNb_{3}O_{8} and KNb_{3}O_{8}. Both demonstrate multi-electron (Nb5+/Nb3+) redox on the first discharge, reacting with ≈5 mol Li per mol ANb_{3}O_{8}. Li intercalation in NaNb_{3}O_{8} is dominated by Li-diffusion kinetics and evolution of the interlayer structure, with Li initially filling octahedral sites near the interlayer space to draw the layers together to form a (2 × 2)_{∞} WR structure. This average structure change pushes Na ions into the square channels, blocking fast Li diffusion down the square channels that provide the fast Li-ion conduction in most WR materials. Upon charge, Li ions incorporated into the octahedral WR sites (ordered vacancies in the layered structure) are extracted, revealing a new, reversible Li site for additional capacity in WR-like materials. The behavior of KNb_{3}O_{8} is similar, but has additional hysteresis associated with its larger counter-cation. While neither layered niobate matches the demonstrated performance of WR materials, by studying them, we identify a route for increased capacity in WR-like frameworks. Additionally, we identify the important role of Li diffusion kinetics and counter-cations in the cycling behavior of WR-derived structures

Transition Metal Migration Can Facilitate Ionic Diffusion in Defect Garnet-Based Intercalation Electrodes

The importance of metal migration during multielectron redox activity has been characterized, revealing a competing demand to satisfy bonding requirements and local strains in structures upon alkali intercalation. The local structural evolution required to accommodate intercalation in Y2(MoO4)3 and Al2(MoO4)3 has been contrasted by operando characterization methods, including X-ray absorption spectroscopy and diffraction, along with nuclear magnetic resonance measurements. Computational modeling further rationalized behavioral differences. The local structure of Y2(MoO4)3 was maintained upon lithiation, while the structure of Al2(MoO4)3 underwent substantial local atomic rearrangements as the more ionic character of the bonds in Al2(MoO4)3 allowed Al to mix off its starting octahedral position to accommodate strain during cycling. However, this mixing was prevented in the more covalent Y2(MoO4)3, which accommodated strain through rotational motion of polyhedral subunits. Knowing that an increased ionic character can facilitate the diffusion of redox-inactive metals when cycling multielectron electrodes offers a powerful design principle when identifying next-generation intercalation hosts

Crystal Structures, Local Atomic Environments, and Ion Diffusion Mechanisms of Scandium-Substituted Sodium Superionic Conductor (NASICON) Solid Electrolytes

The importance of exploring new solid electrolytes for all-solid-state batteries has led to significant interest in NASICON-type materials. Here, the Sc3+-substituted NASICON compositions Na3ScxZr2-x(SiO4)2-x(PO4)1+x (termed N3) and Na2ScyZr2-y(SiO4)1-y(PO4)2+y (termed N2) (x, y = 0 – 1) are studied as model Na+-ion conducting electrolytes for solid-state batteries. The influence of Sc3+ substitution on the crystal structures and local atomic environments has been characterized by powder X-ray diffraction (XRD) and neutron powder diffraction (NPD), as well as solid-state 23Na, 31P, and 29Si nuclear magnetic resonance (NMR) spectroscopy. A phase transition between 295 and 473 K from monoclinic C2/c to rhombohedral R c is observed for the N3 compositions, while N2 compositions crystallize in a rhombohedral R c unit cell in this temperature range. Alternating current (AC) impedance spectroscopy, molecular dynamics (MD) and high temperature 23Na NMR are in good agreement, showing that with a higher Sc3+ concentration, the ionic conductivity (about 10-4 S/cm at 473 K) decreases and the activation energy for ion diffusion increases. 23Na NMR experiments indicate that the nature of the Na+-ion motion is two-dimensional on the local atomic scale of NMR though the long-range diffusion pathways are three-dimensional. In addition, a combination of MD, bond valence, maximum entropy/Rietveld and van Hove correlation methods has been used, to reveal that the Na+-ion diffusion in these NASICON materials is three-dimensional and that there is a continuous exchange of sodium between Na(1) and Na(2) sites

Structural Evolution and Atom Clustering in β-SiAlON: β-Si6−z_{6-z}Alz_zOz_zN8−z_{8-z}

SiAlON ceramics, solid solutions based on the Si$_3$N$_4$ structure, are important, lightweight structural materials with intrinsically high strength, high hardness, and high thermal and chemical stability. Described by the chemical formula β-Si$_{6-z}$Al$_z$O$_z$N$_{8-z}$, from a compositional viewpoint, these materials can be regarded as solid solutions between Si$_3$N$_4$ and Al$_3$O$_3$N. A key aspect of the structural evolution with increasing Al and O ($z$ in the formula) is to understand how these elements are distributed on the β-Si$_3$N$_4$ framework. The average and local structural evolution of highly phase-pure samples of β-Si$_{6-z}$Al$_z$O$_z$N$_{8-z}$ with $z$ = 0.050, 0.075, and 0.125 are studied here, using a combination of X-ray diffraction, NMR studies, and density functional theory calculations. Synchrotron X-ray diffraction establishes sample purity and indicates subtle changes in the average structure with increasing Al content in these compounds. Solid-state magic-angle-spinning $^{27}$Al NMR experiments, coupled with detailed ab initio calculations of NMR spectra of Al in different AlO$_q$N$_{4-q}$ tetrahedra (0 ≤ $q$ ≤ 4), reveal a tendency of Al and O to cluster in these materials. Independently, the calculations suggest an energetic preference for Al-O bond formation, instead of a random distribution, in the β-SiAlON system.C.C. thanks the National Science Foundation for a Graduate Research Fellowship under Grant DGE 1144085. K.J.G. thanks The Winston Churchill Foundation of the United States and the Herchel Smith Scholarship for funding. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE), Office of Science, by Argonne National Laboratory, was supported by the U.S. DOE under Contract DE-AC02-06CH11357. DFT calculations were performed on the Darwin Supercomputer of the University of Cambridge High Performance Computing Service (http://www.hpc.cam.ac.uk/), provided by Dell Inc. using Strategic Research Infrastructure Funding from the Higher Education Funding Council for England and funding from the Science and Technology Facilities Council (U.K.). This work made use of MRL-shared experimental facilities, supported by the MRSEC Program of the NSF under Award DMR 1121053. The MRL is a member of the NSF-funded Materials Research Facilities Network (www.mrfn.org)

Electrochemical Oxidative Fluorination of an Oxide Perovskite

We report on the electrochemical fluorination of the A-site vacant perovskite ReO3 using high-temperature solid-state cells as well as room-temperature liquid electrolytes. Using galvanostatic oxidation and electrochemical impedance spectroscopy, we find that ReO3 can be oxidized by approximately 0.5 equiv of electrons when in contact with fluoride-rich electrolytes. Results from our density functional theory calculations clearly rule out the most intuitive mechanism for charge compensation, whereby F-ions would simply insert onto the A-site of the perovskite structure. Operando X-ray diffraction, neutron total scattering measurements, X-ray spectroscopy, and solid-state 19F NMR with magic-angle spinning were, therefore, used to explore the mechanism by which fluoride ions react with the ReO3 electrode during oxidation. Taken together, our results indicate that a complex structural transformation occurs following fluorination to stabilize the resulting material. While we find that this process of fluorinating ReO3 appears to be only partially reversible, this work demonstrates a practical electrolyte and cell design that can be used to evaluate the mobility of small anions like fluoride that is robust at room temperature and opens new opportunities for exploring the electrochemical fluorination of many new materials

Physiological Properties of Cholinergic and Non-Cholinergic Magnocellular Neurons in Acute Slices from Adult Mouse Nucleus Basalis

The basal forebrain is a series of nuclei that provides cholinergic input to much of the forebrain. The most posterior of these nuclei, nucleus basalis, provides cholinergic drive to neocortex and is involved in arousal and attention. The physiological properties of neurons in anterior basal forebrain nuclei, including medial septum, the diagonal band of Broca and substantia innominata, have been described previously. In contrast the physiological properties of neurons in nucleus basalis, the most posterior nucleus of the basal forebrain, are unknown.Here we investigate the physiological properties of neurons in adult mouse nucleus basalis. We obtained cell-attached and whole-cell recordings from magnocellular neurons in slices from P42-54 mice and compared cholinergic and non-cholinergic neurons, distinguished retrospectively by anti-choline acetyltransferase immunocytochemistry. The majority (70-80%) of cholinergic and non-cholinergic neurons were silent at rest. Spontaneously active cholinergic and non-cholinergic neurons exhibited irregular spiking at 3 Hz and at 0.3 to 13.4 Hz, respectively. Cholinergic neurons had smaller, broader action potentials than non-cholinergic neurons (amplitudes 64+/-3.4 and 75+/-2 mV; half widths 0.52+/-0.04 and 0.33+/-0.02 ms). Cholinergic neurons displayed a more pronounced slow after-hyperpolarization than non-cholinergic neurons (13.3+/-2.2 and 3.6+/-0.5 mV) and were unable to spike at high frequencies during tonic current injection (maximum frequencies of approximately 20 Hz and >120 Hz).Our results indicate that neurons in nucleus basalis share similar physiological properties with neurons in anterior regions of the basal forebrain. Furthermore, cholinergic and non-cholinergic neurons in nucleus basalis can be distinguished by their responses to injected current. To our knowledge, this is the first description of the physiological properties of cholinergic and non-cholinergic neurons in the posterior aspects of the basal forebrain complex and the first study of basal forebrain neurons from the mouse

Containing the burden of infectious diseases is everyone’s responsibility.:A call for an integrated strategy for developing and promoting hygiene behaviour change in home and everyday life

Across the world, health agencies recognize the profound impact of infectious disease on health and prosperity. Equally, they recognize that prevention is central to fighting infection, and that hygiene in home and everyday life (HEDL) is a key part of this. A current driver is the part that hygienei plays in tackling antibiotic resistance, but it also reflects growing numbers of people at greater risk of infection being cared for in the community. Sustaining the quality of state-funded healthcare requires that the public take greater responsibility for their own health, including protecting themselves and their families against infection. Hygiene must be must be everyone’s responsibility. However, if we are to be successful in promoting hygiene as part of public health, there are barriers which need to be overcome. A key issue is the need to balance evidence of the health benefits of hygiene against possible risks, such as environmental impacts and toxicity issues. Another issue is the role of microbes in human health and whether we have become “too clean”. Lack of a unified voice advocating for hygiene means these issues have tended to take precedence. Another barrier to change is public confusion about the need for hygiene and the difference between hygiene and cleanliness. To address this, we must work together to provide the public with a clear, consistent restatement of the importance of hygiene, and to change public perceptions about hygiene and good hygiene practice. This paper is unique because it examines these issues in an integrated manner and focuses on making achievable, constructive recommendations for developing an effective and sustainable approach. The paper lays out a risk management strategy for hygiene in home and everyday life which gives hygiene appropriate priority within the context of environmental and other health concerns. This “targeted hygiene” approach needs to be placed at the heart of a multimodal prevention strategy, alongside vaccination and other interventions. Based on the findings of this paper, we issue a call to action to national and international policy makers, health agencies and health professionals to recognize the need for an integrated, family-centredii approach to hygiene, and provide effective leadership to achieve this. This paper shows that many of the components of a behaviour change strategy are already in place, but need to be integrated rather than developed independently. We also issue a call to scientists, health professionals, environmental and regulatory agencies, immunologists, microbiomists, the private sector (hygiene appliance and product manufacturers) and the media to work together, through innovative research and communication policies. A collaborative effort is vital if we are to overcome barriers to change and action integrated behaviour change programmes that really work. The report represents the consensus views of an international, interdisciplinary group of experts in the field of infection prevention and hygiene. We recognise that this paper leaves many questions unanswered and would welcome further dialogue with stakeholders on how to develop policy. The aim of this paper is to provide a sound basis for such dialogue. At the 2016 launch of the European Human Biomonitoring Initiative, the EU commissioner for food safety said the followingiii which encapsulates the aim of this report. “We must collectively recognise that risk and uncertainty are part and parcel of every decision we take. We need to engage people in a serious and rational debate. But in this world of information overload – from old media and new – information, misinformation, opinions, prejudices, truths, half-truths and un-truths all compete for public attention. We need better communication of science so that people can be better informed about risk assessment and management decisions