Characterization of Electrode Materials for Lithium Ion and Sodium Ion Batteries Using Synchrotron Radiation Techniques

Intercalation compounds such as transition metal oxides or phosphates are the most commonly used electrode materials in Li-ion and Na-ion batteries. ...

Lawrence Berkeley National Laboratory

The (7)Li NMR isotropic shift for olivine LiMPO(4) (M = Fe, Mn, Co, Ni) is assigned to hyperfine coupling between the (7)Li nucleus and the transition metal unpaired electrons on the basis of the Curie-Weiss temperature dependence of the shift. The hyperfine shift arises from a linear combination of Li-O-M through-bond interactions wherein the unpaired A' electrons contribute a negative shift and the unpaired A' ' electrons contribute a positive shift. The hyperfine coupling constant is determined for each composition.

Hyperfine fields at the Li site in LiFePO(4)-type olivine materials for lithium rechargeable batteries: a (7)Li MAS NMR and SQUID study.

Direct imaging of surface molecules and the interfaces between soft and hard materials on functionalized nanoparticles is a great challenge using modern microscopy techniques. We show that graphene, a single atomic layer of sp(2)-bonded carbon atoms, can be employed as an ultrathin support film that enables direct imaging of molecular layers and interfaces in both conventional and atomic-resolution transmission electron microscopy. An atomic-resolution imaging study of the capping layers and interfaces of citrate-stabilized gold nanoparticles is used to demonstrate this novel capability. Our findings reveal the unique potential of graphene as an ideal support film for atomic-resolution transmission electron microscopy of hard and soft nanomaterials.

Direct imaging of soft-hard interfaces enabled by graphene.

We report that the substrate-free gas-phase graphene synthesis method produces clean and highly ordered graphene sheets that are similar in quality to the graphene obtained through the mechanical exfoliation of highly oriented pyrolytic graphite.

Clean and highly ordered graphene synthesized in the gas phase.

The interaction of Li(+) with single and few layer graphene is reported. In situ Raman spectra were collected during the electrochemical lithiation of the single- and few-layer graphene. While the interaction of lithium with few layer graphene seems to resemble that of graphite, single layer graphene behaves very differently. The amount of lithium absorbed on single layer graphene seems to be greatly reduced due to repulsion forces between Li(+) at both sides of the graphene layer.

The interaction of Li+ with single-layer and few-layer graphene.

The manipulation of the bandgap of graphene by various means has stirred great interest for potential applications. Here we show that treatment of graphene with xenon difluoride produces a partially fluorinated graphene (fluorographene) with covalent C-F bonding and local sp(3)-carbon hybridization. The material was characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, electron energy loss spectroscopy, photoluminescence spectroscopy, and near edge X-ray absorption spectroscopy. These results confirm the structural features of the fluorographane with a bandgap of 3.8 eV, close to that calculated for fluorinated single layer graphene, (CF)(n). The material luminesces broadly in the UV and visible light regions, and has optical properties resembling diamond, with both excitonic and direct optical absorption and emission features. These results suggest the use of fluorographane as a new, readily prepared material for electronic, optoelectronic applications, and energy harvesting applications.

Fluorographene: a wide bandgap semiconductor with ultraviolet luminescence.

Localized surface plasmon absorption features arise at high doping levels in semiconductor nanocrystals, appearing in the near-infrared range. Here we show that the surface plasmons of tin-doped indium oxide nanocrystal films can be dynamically and reversibly tuned by postsynthetic electrochemical modulation of the electron concentration. Without ion intercalation and the associated material degradation, we induce a > 1200 nm shift in the plasmon wavelength and a factor of nearly three change in the carrier density.

Dynamically modulating the surface plasmon resonance of doped semiconductor nanocrystals.

The properties of mesoporous materials hinge on control of their composition, pore dimensions, wall thickness, and the size and shape of the crystallite building units. We create ordered mesoporous materials in which all of these parameters are independently controlled. Different sizes (from 4.5 to 8 nm) and shapes (spheres and rods) of ligand-stripped nanocrystals are assembled using the same structure-directing block copolymers, which contain a tethering domain designed to adsorb to their naked surfaces. Material compositions range from metal oxides (Sn-doped In(2)O(3) or ITO, CeO(2), TiO(2)) to metal fluorides (Yb,Er-doped NaYF(4)) and metals (FePt). The incorporation of new types of nanocrystals into mesoporous architectures can lead to enhanced performance. For example, TiO(2) nanorod-based materials withstand >1000 electrochemical cycles without significant degradation.

Assembly of ligand-stripped nanocrystals into precisely controlled mesoporous architectures.

Through soft X-ray absorption spectroscopy, hard X-ray Raman scattering, and theoretical simulations, we provide the most in-depth and systematic study of the phase transformation and (de)lithiation effect on electronic structure in Li(x)FePO(4) nanoparticles and single crystals. Soft X-ray reveals directly the valence states of Fe 3d electrons in the vicinity of Fermi level, which is sensitive to the local lattice distortion, but more importantly offers detailed information on the evolution of electronic states at different electrochemical stages. The soft X-ray spectra of Li(x)FePO(4) nanoparticles evolve vividly with the (de)lithiation level. The spectra fingerprint the (de)lithiation process with rich information on Li distribution, valency, spin states, and crystal field. The high-resolution spectra reveal a subtle but critical deviation from two-phase transformation in our electrochemically prepared samples. In addition, we performed both first-principles calculations and multiplet simulations of the spectra and quantitatively determined the 3d valence states that are completely redistributed through (de)lithiation. This electronic reconfiguration was further verified by the polarization-dependent spectra collected on LiFePO(4) single crystals, especially along the lithium diffusion direction. The evolution of the 3d states is overall consistent with the local lattice distortion and provides a fundamental picture of the (de)lithiation effects on electronic structure in the Li(x)FePO(4) system.

Phase transformation and lithiation effect on electronic structure of Li(x)FePO4: an in-depth study by soft X-ray and simulations.

Gr&acirc;ce &agrave; la spectroscopie d&#39;absorption des rayons x mou, la diffusion Raman des rayons x dure et simulations th&eacute;oriques, nous fournissons l&#39;&eacute;tude plus approfondie et syst&eacute;matique de la transformation de phase et l&#39;effet lithiation (de) sur la structure &eacute;lectronique de nanoparticules de Li(x)FePO(4) et de monocristaux. Rayons x mou r&eacute;v&egrave;lent directement les &Eacute;tats de valence de Fe &eacute;lectrons 3d &agrave; proximit&eacute; du niveau de Fermi, qui est sensible &agrave; la d&eacute;formation du r&eacute;seau local, mais plus offre surtout des informations d&eacute;taill&eacute;es sur l&#39;&eacute;volution des &Eacute;tats &eacute;lectroniques &agrave; diff&eacute;rents stades &eacute;lectrochimiques. Les spectres de rayons x mous de nanoparticules Li(x)FePO(4) &eacute;voluent avec &eacute;clat avec le niveau de lithiation (de). Les spectres d&#39;empreintes digitales le processus (de) de lithiation avec riches informations sur Li distribution, Valence, &Eacute;tats de spin et champ cristallin. Les spectres de haute r&eacute;solution r&eacute;v&egrave;lent une d&eacute;viation subtile mais critique de transformation en deux phases dans nos &eacute;chantillons pr&eacute;par&eacute;s par voie &eacute;lectrochimique. En outre, nous avons effectu&eacute; les calculs des premiers principes et des simulations de multiplet des spectres et d&eacute;termin&eacute; quantitativement les &Eacute;tats 3d de valence qui sont compl&egrave;tement redistribu&eacute;s par le biais de lithiation (de). Cette reconfiguration &eacute;lectronique a &eacute;galement v&eacute;rifi&eacute;e les spectres d&eacute;pendant de la polarisation recueillies sur monocristaux LiFePO(4), surtout le long de la direction de diffusion au lithium. L&#39;&eacute;volution des &Eacute;tats 3d est globalement conforme &agrave; la distorsion du r&eacute;seau local et fournit une image fondamentale de la (de) lithiation effets sur la structure &eacute;lectronique du syst&egrave;me Li(x)FePO(4).

La phase de transformation et la lithiation effet sur la structure &eacute;lectronique de Li (x) FePO4 : une &eacute;tude approfondie par les doux rayons x et les simulations.

Attraverso la spettroscopia di assorbimento di raggi x molle, scattering Raman di raggi x duri e simulazioni teoriche, forniamo lo studio pi&ugrave; approfondito e sistematico della trasformazione di fase e (de) lithiation effetto sulla struttura elettronica di nanoparticelle Li(x)FePO(4) e cristalli singoli. Raggi x molli rivela direttamente gli Stati di valenza del Fe elettroni 3d in prossimit&agrave; del livello di Fermi, che &egrave; sensibile alla distorsione reticolare locale, ma pi&ugrave; d&#39;importanza offre informazioni dettagliate sull&#39;evoluzione degli Stati elettronici nelle diverse fasi di elettrochimiche. Gli spettri dei raggi x molli di nanoparticelle Li(x)FePO(4) evolvono vivacemente con il livello di lithiation (de). Gli spettri di impronte digitali il processo di (de) lithiation con ricche informazioni sulla distribuzione, Valenza, Stati di spin e campo di cristallo Li. Gli spettri ad alta risoluzione rivelano una sottile ma fondamentale deviazione dalla trasformazione bifase nei nostri campioni elettrochimicamente preparati. Inoltre, abbiamo eseguito sia i principi primi calcoli e simulazioni multipletto degli spettri e quantitativamente determinato gli Stati di valenza 3d che sono completamente ridistribuiti attraverso lithiation (de). Questa riconfigurazione elettronica &egrave; stato ulteriormente verificato dallo spettro di polarizzazione-dipendente raccolto su singoli cristalli LiFePO(4), soprattutto lungo la direzione di diffusione del litio. L&#39;evoluzione degli Stati 3d &egrave; in generale coerente con la distorsione del reticolo locale e fornisce un quadro fondamentale di (de) lithiation effetti sulla struttura elettronica del sistema Li(x)FePO(4).

Fase di trasformazione e lithiation effetto sulla struttura elettronica di Li (x) FePO4: uno studio approfondito da morbido a raggi x e simulazioni.

Rechargeable lithium or lithium-ion cells can be overcharge-protected by an electroactive polymer composite separator. The use of non-woven fibrous membranes instead of conventional microporous membranes as the composite substrates allowed better distribution of the electroactive polymer, which led to improved utilization and a 40-fold increase in sustainable current density. For the first time, stable overcharge protection for hundreds of cycles was demonstrated in several cell chemistries, including LiNi1/3Co1/3Mn1/3O2, LiFePO4, and spinel Li1.05Mn1.95O4 half-cells. Protection at a charging rate as high as 5 C was achieved at a steady state cell potential below 4.85 V.

Stable and high-rate overcharge protection for rechargeable lithium batteries.

The chemical phase distribution in hydrothermally grown micrometric single crystals LiFePO4 following partial chemical delithiation was investigated. Full field and scanning X-ray microscopy were combined with X-ray absorption spectroscopy at the Fe K- and O K-edges, respectively, to produce maps with high chemical and spatial resolution. The resulting information was compared to morphological insight into the mechanics of the transformation by scanning transmission electron microscopy. This study revealed the interplay at the mesocale between microstructure and phase distribution during the redox process, as morphological defects were found to kinetically determine the progress of the reaction. Lithium deintercalation was also found to induce severe mechanical damage in the crystals, presumably due to the lattice mismatch between LiFePO4 and FePO4. Our results lead to the conclusion that rational design of intercalation-based electrode materials, such as LiFePO4, with optimized utilization and life requires the tailoring of particles that minimize kinetic barriers and mechanical strain. Coupling TXM-XANES with TEM can provide unique insight into the behavior of electrode materials during operation, at scales spanning from nanoparticles to ensembles and complex architectures.

Thomas J. Richardson

Environmental Energy Technologies Division

Lawrence Berkeley National Laboratory

Characterization of Electrode Materials for Lithium Ion and Sodium Ion Batteries Using Synchrotron Radiation Techniques

Thomas J. Richardson

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Environmental Energy Technologies Division

Lawrence Berkeley National Laboratory

Characterization of Electrode Materials for Lithium Ion and Sodium Ion Batteries Using Synchrotron Radiation Techniques

Environmental Energy Technologies Division