Michaël Deschamps

Exploring electrolyte organization in supercapacitor electrodes with solid-state NMR.

Supercapacitors are electrochemical energy-storage devices that exploit the electrostatic interaction between high-surface-area nanoporous electrodes and electrolyte ions. Insight into the molecular mechanisms at work inside supercapacitor carbon electrodes is obtained with (13)C and (11)B ex situ magic-angle spinning nuclear magnetic resonance (MAS-NMR). In activated carbons soaked with an electrolyte solution, two distinct adsorption sites are detected by NMR, both undergoing chemical exchange with the free electrolyte molecules. On charging, anions are substituted by cations in the negative carbon electrode and cations by anions in the positive electrode, and their proportions in each electrode are quantified by NMR. Moreover, acetonitrile molecules are expelled from the adsorption sites at the negative electrode alone. Two nanoporous carbon materials were tested, with different nanotexture orders (using Raman and (13)C MAS-NMR spectroscopies), and the more disordered carbon shows a better capacitance and a better tolerance to high voltages.

High reversible capacity carbon-lithium negative electrode in polymer electrolyte

Abstract Cabonaceous materials from different types are used in polymer electrolyte-based lithium cells in order to evaluate their electrochemical performance during lithium storage in the application as the negative electrode in lithium-ion-type batteries. The formation of a passivating film during the first cathodic polarization may account for the low faradaic yield of the first cycle. It also plays an important role in the stabilization of the carbon/polymer electrolyte interface. Non-graphitized mesocarbon micro beads lead to a higher reversible capacity of 410 mAh/g than the graphitized one. It is suggested that lithium could be reversibly stored as a multilayer ‘deposit’ at the carbon surface. A model of epitaxial lithium electroplating is presented.

LiZnSO4F Made in an Ionic Liquid: A Ceramic Electrolyte Composite for Solid-State Lithium Batteries

The search for good solid electrolytes constitutes a major goal towards the development of safer lithium batteries. A few candidates do exist, but they suffer either from narrow electrochemical window stability or too low ionic conductivity. Herein we report the ionic-liquid-assisted synthesis of a novel LiZnSO4F fluorosulfate phase having a sillimanite LiTiOPO4-type structure, which on simply pressed samples shows a room-temperature ionic conductivity of 10 – 10 7 Scm 1 together with a 0–5 V electrochemical stability window range, while ionic-liquid-free LiZnSO4F shows an ionic conductivity four orders of magnitude lower (10 11 Scm ). While robustly reproducible but not yet fully understood, this finding offers new opportunities to tailor inorganic composites with higher ionic conductivity. The origin of such results is demonstrated to be rooted in a surface effect associated with the grafting of a lithium-containing ionic liquid layer. This finding opens up new opportunities for the design of ceramic composites with higher ionic conductivity and should serve as an impetus for further exploiting the chemistry of ionic liquid grafting on oxides. Renewable energy sources and electric automotive transportation are popular topics in today s energy-conscious society, hence placing rechargeable batteries as one of the major technological sciences in this new century. Advances in energy storage are a tribute to chemists abilities to design new and better materials. In the hunt for novel electrode materials, notions of sustainability must be considered. This is the reason why LiFePO4, which is made of inexpensive and abundant chemical elements, has attracted the attention of the research community despite its poor conducting properties. By particle downsizing and carbon nanocoating, LiFePO4/C composite overcomes transport limitations and is capable of reversibly and rapidly intercalating 0.9 Li (ca. 160 mA hg ) at a redox voltage of 3.43 V versus Li. Thus, it has become one of the most praised electrode materials for the next generation of rechargeable batteries for high-volume applications. Further exploring the chemistry of polyanionic-based insertion electrodes, we recently synthesized, by an ionothermal process, a novel 3.6 V LiFeSO4F electrode showing a reversible capacity nearing 140 mAh g 1 (theoretical capacity = 151 mAh g ), good rate capability, and cycling stability. This fluorosulfate was found to crystallize in a tavorite structure (space group P 1) with three-dimensional channels for Li diffusion as opposed to the one-dimensional channels in LiFePO4. Most likely, from the 3D versus 1D change in the conduction path, the use of LiFeSO4F powders will obviate the need for nanosizing or carbon coating, while the same cost and environmental advantages are maintained. Since our early report, we have considerably enlarged the fluorosulfate family with the discovery of AMSO4F (A = Li, Na and M = Co, Ni, Mn, etc.) homologues. This new family of materials, practically unknown a year ago, counts no less than 20 members showing related structures with either promising electrochemical or attractive ionic properties. Among them, the sodium-based 3d-metal fluorosulfates, which crystallize in a titanite structure (derived from the tavorite structure, space group P21/c) and have localized positions for the Na ions, were found to show a four-fold increase in ionic conductivity as compared to their Li-based counterparts on cold-pressed powders (10 7 S cm 1 for Na vs. 10 11 Scm 1 for Li at room temperature). While far from the hallmark solid-state electrolytes for future Li batteries such as Li1.5Al0.5Ge1.5(PO4)3 (LAG), Li1.3Al0.3Ti1.7(PO4)3 (LAT), and Li3+xPO4 xNx (LIPON), which have room-temperature conductivities of 2.8 10 4 Scm , 10 3 S cm , and 10 6 S cm , respectively, such a finding was an impetus to look for further fluorosulfate members as part of the effort to develop new ceramic electrolyte materials with increased conductivity, thus allowing a switch from thin-film to bulk technology in all solid-state batteries. Besides high ionic conductivity, a pivotal figure of merit for solid-state electrolytes is the width of their electrochemical stability window. This window is limited for ionic conducting ceramics containing 3d-metal elements, such as Li1.3Al0.3Ti1.7(PO4)3, owing to the reduction of Ti 4+ in Ti at approximately 2.4 V. So our strategy was to search for other members of the fluorosulfate AMSO4F family containing divalent metals that cannot be easily reduced or oxidized. Besides LiMgSO4F, the first reported fluorosulfate, [7] other attractive candidates could enlist lead, tin, or zinc to prepare AMSO4F phases. Mindful of the previously reported struc[*] Dr. P. Barpanda, Dr. J.-N. Chotard, Dr. C. Delacourt, M. Reynaud, Prof. M. Armand, Prof. J.-M. Tarascon Laboratoire de R activit et Chimie des Solides Universit de Picardie Jules Verne, CNRS UMR 6007 33, rue Saint Leu, 80039 Amiens (France) E-mail: jean-marie.tarascon@sc.u-picardie.fr Homepage: http://jmtarascon.tech.officelive.com

Carbon fibres and natural graphite as negative electrodes for lithium ion-type batteries

Abstract Carbon fibres (CFs), from different origins, and natural graphite are used as host lattices for lithium electrochemical intercalation and de-intercalation in organic liquid and solid polymer electrolytes, respectively. In both systems, irreversible behaviour occurred during the first cycle of which the origin is tentatively discussed. The reversible capacity of the mesophase CFs-based electrodes, which is related to the total relative amount of lithium exchanged with the electrolyte during the charge/discharge operations, is found to increase with their crystallinity. Some thermodynamic data associated with the formation of the stage-1 graphite-lithium compound in polymer electrolyte-based cells are determined.

Topological, Geometric, and Chemical Order in Materials: Insights from Solid-State NMR

Unlike the long-range order of ideal crystalline structures, local order is an intrinsic characteristic of real materials and often serves as the key to the tuning of their properties and their final applications. Although researchers can easily assess local ordering using two-dimensional imaging techniques with resolution that approaches the atomic level, the diagnosis, description, and qualification of local order in three dimensions is much more challenging. Solid-state nuclear magnetic resonance (NMR) and its panel of continually developing instruments and methods enable the local, atom-selective characterization of structures and assemblies ranging from the atomic to the nanometer length scales. By making use of the indirect J-coupling that distinguishes chemical bonds, researchers can use solid-state NMR to characterize a variety of materials, ranging from crystalline compounds to amorphous or glassy materials. In crystalline compounds showing some disorder, we describe and distinguish the contributions of topology, geometry, and local chemistry in ways that are consistent with X-ray diffraction and computational approaches. We give examples of materials featuring either chemical disorder in a topological order or topological disorder with local chemical order. For glasses, we show that we can separate geometric and chemical contributions to the local order by identifying structural motifs with a viewpoint that extends from the atomic scale up to the nanoscale. As identified by solid state NMR, the local structure of amorphous materials or glasses consists of well-identified structural entities up to at least the nanometer scale. Instead of speaking of disorder, we propose a new description for these structures as a continuous assembly of locally defined structures, an idea that draws on the concept of locally favored structures (LFS) introduced by Tanaka and coworkers. This idea provides a comprehensive picture of amorphous structures based on fluctuations of chemical composition and structure over different length scales. We hope that these local or molecular insights will allow researchers to consider key questions related to nucleation and crystallization, as well as chemically (spinodal decomposition) or density-driven (polyamorphism) phase separation, which could lead to future applications in a variety of materials.

Superadiabaticity in magnetic resonance

Adiabaticity plays a central role in modern magnetic resonance experiments, as excitations with adiabatic Hamiltonians allow precise control of the dynamics of the spin states during the course of an experiment. Surprisingly, many commonly used adiabatic processes in magnetic resonance perform well even though the adiabatic approximation does not appear to hold throughout the process. Here we show that this discrepancy can now be explained through the use of Berrys superadiabatic formalism, which provides a framework for including the finite duration of the process in the theoretical and numerical treatments. In this approach, a slow, but finite time-dependent Hamiltonian is iteratively transformed into time-dependent diagonal frames until the most accurate adiabatic approximation is obtained. In the case of magnetic resonance, the magnetization during an adiabatic process of finite duration is not locked to the effective Hamiltonian in the conventional adiabatic frame, but rather to an effective Hamiltonian in a superadiabatic frame. Only in the superadiabatic frame can the true validity of the adiabatic approximation be evaluated, as the inertial forces acting in this frame are the true cause for deviation from adiabaticity and loss of control during the process. Here we present a brief theoretical background of superadiabaticity and illustrate the concept in the context of magnetic resonance with commonly used shaped radio-frequency pulses.

Connectivity and Proximity between Quadrupolar Nuclides in Oxide Glasses: Insights from through-Bond and through-Space Correlations in Solid-State NMR

The connectivity and proximity among framework cations and anions in covalent oxide glasses yields unique information whereby their various transport and thermodynamic properties can be predicted. Recent developments and advances in the reconstruction of anisotropic spin interactions among quadrupolar nuclides (spin > (1)/(2)) in solid-state NMR shed light on a new opportunity to explore local connectivity and proximity in amorphous solids. Here, we report the 2D through-bond (J-coupling) and through-space (dipolar coupling) correlation NMR spectra for oxide glasses where previously unknown structural details about the connectivity and proximity among quadrupolar nuclides ((27)Al, (17)O) are determined. Nonbridging oxygen peaks in Ca-aluminosilicate glasses with distinct connectivity, such as Ca-O-Al and Al-O-(Al, Si) are well distinguished in {(17)O}(27)Al solid HMQC NMR spectra. Both peaks shift to a lower frequency in direct and indirect dimensions upon the addition of Si to the Ca-aluminate glasses. The 2D (27)Al double quantum magic angle spinning NMR spectra for Mg-aluminoborate glasses indicate the preferential proximity between ([4])Al and ([5])Al leading to the formation of correlations peaks such as ([4])Al-([4])Al, ([4])Al-([5])Al, and ([5])Al-O-([5])Al. A fraction of the ([6])Al-([6])Al correlation peak is also noticeable while that of ([4,5])Al-([6])Al is missing. These results suggest that ([6])Al is likely to be isolated from the ([4])Al and ([5])Al species, forming ([6])Al clusters. The experimental realization of through-bond and through-space correlations among quadrupolar nuclides in amorphous materials suggests a significant deviation from the random distribution among framework cations and a spatial heterogeneity due to possible clustering of framework cations in the model oxide glasses.

Spin-counting NMR experiments for the spectral editing of structural motifs in solids

Scalar couplings, recoupled or full dipolar interactions can be used to characterize multinuclear structural molecular motifs in solids, by counting the neighbouring spins in solid-state NMR, opening new ways for the differentiation of overlapping spectral responses which is a limiting factor in many high resolution experiments carried out on disordered systems.

1H and 19F ultra-fast MAS double-quantum single-quantum NMR correlation experiments using three-spin terms of the dipolar homonuclear Hamiltonian

Measuring internuclear distances through dipolar interaction is a major challenge for solid-state nuclear magnetic resonance (NMR) spectroscopy. Obtaining reliable interatomic distances provides an access to the local structure in ordered or disordered solids. We show that at magic angle spinning (MAS) frequencies larger than ca. 50 kHz, some of the three-spin terms of the homogeneous homonuclear dipolar Hamiltonian can be used to promote the creation of double-quantum coherences between neighbouring (1)H or (19)F spins without using dipolar recoupling pulse sequences in the Dipolar Homonuclear Homogeneous Hamiltonian (DH(3)) double-quantum/single-quantum correlation experiment. This makes it possible to probe inter-nuclear spatial proximity with limited risk of probe or sample damage from radio-frequency (RF) irradiation, and is fully appropriate for fast repetition rate offering sensitivity gains in favourable cases. Experimental demonstrations are supported by multi-spin numerical simulations, which points to new possibilities for the characterization of spin-system geometries.

Great reversible capacity of carbon lithium electrode in solid polymer electrolyte

The reversible storage capacity of lithium in a mesophase-derived semi-coke, heat-treated (HTT) below 700°C, was found by far exceeding the theoretical value corresponding to the LiC6 composition. A capacity as high as 1660 mAh/g was obtained in the case of carbon, heat-treated at ∼ 450 °C, when poly(ethylene oxide)-based electrolyte is used in lithium cells operated at 100 °C. This great capacity is discussed on the basis of a model where lithium forms multilayers on the external basal surfaces of the nanometric size mesocarbon domains.