characterization-electrode-materials-for-lithium-ion-sodium-ion

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

University of Illinois at Chicago

Antifluorite-type lithium chromium oxide nitrides were prepared by solid-state reaction of Li(3)N, Li(2)O, and Cr(2)N. Depending on the reaction time and starting Li/Cr and O/Cr ratios, either an ordered or a disordered phase (or mixtures of both) is obtained. The formation of the former is favored by short reaction times and low Cr/O ratios whereas the formation of the latter is favored by higher Cr/O ratios and longer reaction times. The two phases were characterized, and the first one was confirmed to be the already reported Li(14)Cr(2)N(8)O phase, whereas the stoichiometry of the second is Li(10)CrN(4)O(2). Interestingly, even if both contain cationic vacancies in the structure, electrochemical lithium intercalation could only be achieved for Li(10)CrN(4)O(2). This phase exhibits a reversible capacity of 160 mAh/g very stable upon cycling. Bond valence and first-principles DFT calculations were carried out to understand the absence of lithium insertion in Li(14)Cr(2)N(8)O. Li-Li repulsion and destabilization of the tetrahedral CrN(4) units induced by occupation of the potential sites, as well as the absence of energetically favorable pathways for transport of the ions to these sites, are suggested to be the reasons.

Antifluorite-type lithium chromium oxide nitrides: synthesis, structure, order, and electrochemical properties.

The layered oxysulfides Sr2MnO2Cu2m-0.5Sm+1 (m = 1-3) consist of alternating perovskite-type Sr2MnO2 layers and copper sulfide layers. The copper ions can be replaced electrochemically and reversibly by Li. The lithiated materials were studied by Li MAS NMR, and Li resonances were observed with shifts that could be rationalized based on the number of sulfide layers. The materials were cycled versus Li and showed enhanced capacity retention in comparison to pure Cu2S; the good electrochemical performance was ascribed to the presence of the layered framework structure and rapid Li+ and Cu+ conductivity in the sulfide layers.

Layered oxysulfides Sr2MnO2Cu2m-0.5Sm+1 (m = 1, 2, and 3) as insertion hosts for Li ion batteries.

A crystal-chemical exploration of part of the Li-Mn-N-O system was carried out. Several samples were synthesized using Li(3)N, Mn(x)N and Li(2)O and characterized with chemical analysis, XRD, XAS, and NMR. An increase in the starting proportion of Li(2)O increases the amounts of lithium and oxygen in the compounds, but, according to the XANES Mn K-edge spectra, all the oxynitrides still contain Mn(5+) ions preferentially coordinated by N(3-), forming [MnN(4)] tetrahedra. The analysis of the position of these samples in the compositional Li(3)N-Li(2)O-MnN(x) ternary phase diagram and the plot of their cell parameters against the oxygen molar fraction indicates that all the oxynitrides belong to the same tie-line, which also includes Li(2)O but not Li(7)MnN(4). Although the XRD patterns suggest that these samples crystallize in a disordered antifluorite-type structure, the analysis of the (6)Li NMR data indicates that short-range ordering does exist. The performance as electrode materials in lithium batteries of the synthesized samples was also evaluated. Li(7.9)MnN(3.2)O(1.6) was shown to be the most attractive candidate because of its higher capacity values and improved retention upon cycling with respect to the other members of the series.

Synthesis, short-range structure, and electrochemical properties of new phases in the Li-Mn-N-O system.

Despite the imminent commercial introduction of Li-ion batteries in electric drive vehicles and their proposed use as enablers of smart grids based on renewable energy technologies, an intensive quest for new electrode materials that bring about improvements in energy density, cycle life, cost, and safety is still underway. This Progress Report highlights the recent developments and the future prospects of the use of phases that react through conversion reactions as both positive and negative electrode materials in Li-ion batteries. By moving beyond classical intercalation reactions, a variety of low cost compounds with gravimetric specific capacities that are two-to-five times larger than those attained with currently used materials, such as graphite and LiCoO(2), can be achieved. Nonetheless, several factors currently handicap the applicability of electrode materials entailing conversion reactions. These factors, together with the scientific breakthroughs that are necessary to fully assess the practicality of this concept, are reviewed in this report.

Beyond intercalation-based Li-ion batteries: the state of the art and challenges of electrode materials reacting through conversion reactions.

The ability to probe morphology and phase distribution in complex systems at multiple length scales unravels the interplay of nano- and micrometer-scale factors at the origin of macroscopic behavior. While different electron- and X-ray-based imaging techniques can be combined with spectroscopy at high resolutions, owing to experimental time limitations the resulting fields of view are too small to be representative of a composite sample. Here a new X-ray imaging set-up is proposed, combining full-field transmission X-ray microscopy (TXM) with X-ray absorption near-edge structure (XANES) spectroscopy to follow two-dimensional and three-dimensional morphological and chemical changes in large volumes at high resolution (tens of nanometers). TXM XANES imaging offers chemical speciation at the nanoscale in thick samples (>20 µm) with minimal preparation requirements. Further, its high throughput allows the analysis of large areas (up to millimeters) in minutes to a few hours. Proof of concept is provided using battery electrodes, although its versatility will lead to impact in a number of diverse research fields.

Three-dimensional imaging of chemical phase transformations at the nanoscale with full-field transmission X-ray microscopy.

A study of the correlations between the stoichiometry, secondary phases and transition metal ordering of LiNi(0.5)Mn(1.5)O(4) was undertaken by characterizing samples synthesized at different temperatures. Insight into the composition of the samples was obtained by electron microscopy, neutron diffraction and X-ray absorption spectroscopy. In turn, analysis of cationic ordering was performed by combining neutron diffraction with Li MAS NMR spectroscopy. Under the conditions chosen for the synthesis, all samples systematically showed an excess of Mn, which was compensated by the formation of a secondary rock salt phase and not via the creation of oxygen vacancies. Local deviations from the ideal 3:1 Mn:Ni ordering were found, even for samples that show the superlattice ordering by diffraction, with different disordered schemes also being possible. The magnetic behavior of the samples was correlated with the deviations from this ideal ordering arrangement. The in-depth crystal-chemical knowledge generated was employed to evaluate the influence of these parameters on the electrochemical behavior of the materials.

Composition-structure relationships in the Li-ion battery electrode material LiNi(0.5)Mn(1.5)O(4).

Monodisperse Sn spherical nanocrystals of 10.0 ± 0.2 nm were prepared in dispersible colloidal form. They were used as a model platform to study the impact of size on the accommodation of colossal volume changes during electrochemical lithiation using ex situ transmission electron microscopy (TEM). Significant mechanical damage was observed after full lithiation, indicating that even crystals at these very small dimensions are not sufficient to prevent particle pulverization that compromises electrode durability.

Monodisperse Sn nanocrystals as a platform for the study of mechanical damage during electrochemical reactions with Li.

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.

Mesoscale phase distribution in single particles of LiFePO4 following lithium deintercalation.

A series of layered oxides within the Na(x)Ni(ix/2)Mn(1-x/2)O2 (2/3 ≤ x ≤ 1) system were synthesized by classical solid-state methodologies. A study of their long and short-range structure was undertaken by combining X-ray diffraction and NMR spectroscopy. A transition from P2 to O3 stacking was observed at x > 0.8 when samples were made at 900 °C, which was accompanied by disordering of ions in the transition metal layer. The magnetic properties of the materials were consistent with this picture of ordering, with all samples showing antiferromagnetic character. At x = 2/3, competition between a P2 and a P3 structure, with different degrees of transition metal ordering, was found depending on the synthesis temperature. Na/Li exchange led to structures with octahedral or tetrahedral coordination of the alkali metal, and Li/Ni crystallographic exchange in the resulting O3 phases. The transition from alkali metal prismatic coordination to octahedral/tetrahedral coordination involves [TMO6]∞ layer shearing that induces some structural disorder through the formation of stacking faults.

Article	Year
Antifluorite-type lithium chromium oxide nitrides: synthesis, structure, order, and electrochemical properties. Inorganic chemistry\| PubMed ID: 15500342	2004
Layered oxysulfides Sr2MnO2Cu2m-0.5Sm+1 (m = 1, 2, and 3) as insertion hosts for Li ion batteries. Journal of the American Chemical Society\| PubMed ID: 17031937	2006
Synthesis, short-range structure, and electrochemical properties of new phases in the Li-Mn-N-O system. Inorganic chemistry\| PubMed ID: 19405540	2009
Beyond intercalation-based Li-ion batteries: the state of the art and challenges of electrode materials reacting through conversion reactions. Advanced materials (Deerfield Beach, Fla.)\| PubMed ID: 20730811	2010
Three-dimensional imaging of chemical phase transformations at the nanoscale with full-field transmission X-ray microscopy. Journal of synchrotron radiation\| PubMed ID: 21862859	2011
Composition-structure relationships in the Li-ion battery electrode material LiNi(0.5)Mn(1.5)O(4). Chemistry of materials : a publication of the American Chemical Society\| PubMed ID: 23002325	2012
Monodisperse Sn nanocrystals as a platform for the study of mechanical damage during electrochemical reactions with Li. Nano letters\| PubMed ID: 23477483	2013
Mesoscale phase distribution in single particles of LiFePO4 following lithium deintercalation. Chemistry of materials : a publication of the American Chemical Society\| PubMed ID: 23745016	2013
Study of the transition metal ordering in layered Na(x)Ni(x/2)Mn(1-x/2)O2 (2/3 ≤ x ≤ 1) and consequences of Na/Li exchange. Inorganic chemistry\| PubMed ID: 23909957	2013

Jordi Cabana

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