The incident X-ray beam; n is an integer. This observation is an example of X-ray wave interference (Roentgenstrahlinterferenzen), commonly known as X-ray diffraction (XRD), and was direct evidence for the periodic atomic structure of crystals postulated for several centuries. N l =2dsinq Bragg’s Law. The incident X-ray beam; n is an integer. This observation is an example of X-ray wave interference (Roentgenstrahlinterferenzen), commonly known as X-ray diffraction (XRD), and was direct evidence for the periodic atomic structure of crystals postulated for several centuries. N l =2dsinq Bragg’s Law.
Mapping Performance Variations to See How Lithium-Metal Batteries Fail
Using high-energy x-rays, scientists probed different points across a high-energy-density lithium-metal battery—of interest for long-range electric vehicles—and used the data to identify the main failure mechanism
April 19, 2021enlarge
Brookhaven Lab chemist and Stony Brook University (SBU) professor Peter Khalifah (middle) with SBU graduate students Zhuo Li (left) and Gerard Mattei (right) holding a 'pouch cell' battery attached to a frame used for synchrotron x-ray studies. Note: This photo was taken prior to current COVID-19 social distancing guidelines.
UPTON, NY—Scientists have identified the primary cause of failure in a state-of-the-art lithium-metal battery, of interest for long-range electric vehicles. Using high-energy x-rays, they followed the cycling-induced changes at thousands of different points across the battery and mapped the variations in performance. At each point, they used the x-ray data to calculate the amount of cathode material and its local state of charge. These findings, combined with complementary electrochemical measurements, enabled them to determine the dominant mechanism driving the loss of battery capacity after many charge-discharge cycles. As they recently reported in Chemistry of Materials, depletion of the liquid electrolyte was the primary cause of failure. The electrolyte transports lithium ions between the rechargeable battery’s two electrodes (anode and cathode) during each charge and discharge cycle.
“The big advantage of batteries with anodes made of lithium metal instead of graphite, the material typically used in today’s batteries, is their high energy density,” explained corresponding author Peter Khalifah, a joint appointee in the Chemistry Division at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and the Department of Chemistry at Stony Brook University. “Increasing the amount of energy that a battery material can store for a given mass is the best way to extend the driving range of electric vehicles.”
Since 2017, the Battery500 Consortium—a group of national labs and universities—has been working to develop next-generation lithium-metal anodes with an energy density three times higher than that of current automotive batteries. However, getting lithium metal to work well as an anode in a continually cycling rechargeable battery with a high energy density is extremely challenging. Lithium metal is very reactive, so more and more of it degrades as the battery cycles. Over time, these degradation reactions consume other key battery parts, like the liquid electrolyte.enlarge
Cassidy Anderson, a PNNL post-bachelor intern and Battery500 Consortium team member, holds a pouch cell battery in PNNL's Advanced Battery Facility. The battery is enclosed in a polymer-based pouch containing an aluminum barrier layer to keep it safely sealed in an air-free environment. Photo courtesy of Andrea Starr Pacific Northwest National Laboratory.
Early on in their development, high-energy-density lithium-metal anodes had a very short lifetime, typically 10 cycles or less. Battery500 Consortium researchers improved this lifetime to 200 cycles for the battery cell studied in this work and, more recently, to 400 cycles in 2020. Ultimately, the consortium seeks to achieve lifetimes of 1,000 cycles or more to meet electric vehicle needs.
“How can we make high-energy-density lithium-metal batteries that cycle for a longer time?” said Khalifah. “One way of answering this question is to understand the failure mechanism in a realistic “pouch cell” battery. That’s where our work, supported by the Battery500 Consortium, comes in.”
Widely used in industrial applications, a pouch cell is a sealed rectangular-shaped battery, which uses space much more efficiently than cylindrical cells powering household electronics. Thus, it’s optimal for packing inside vehicles. In this study, scientists from DOE’s Pacific Northwest National Laboratory (PNNL) used PNNL’s Advanced Battery Facility to fabricate lithium-metal batteries in a prototype pouch cell geometry with multiple layers.
Next, scientists from DOE’s Idaho National Laboratory (INL) performed electrochemical testing on one of the multilayer pouch cells. They found only about 15 percent of the cell’s capacity was lost over the first 170 cycles, but 75 percent was lost over the next 25 cycles. To understand this rapid capacity loss near the end of the battery’s life, they extracted one of the cell’s seven cathode layers and sent it to Brookhaven Lab for studies at the X-ray Powder Diffraction (XPD) beamline of the National Synchrotron Light Source II (NSLS-II).enlarge
A schematic of the high-energy x-ray powder diffraction setup. Using automated software, the team mapped the battery state of charge (SOC) based on the diffraction data they collected for thousands of points across the battery.
In XPD, x-rays striking a sample only reflect at certain angles, producing a characteristic pattern. This diffraction pattern provides information on many aspects of the sample’s structure, including the volume of its unit cell—the smallest repeating portion of the structure—and the positions of atoms within the unit cell.
Though the team primarily wanted to learn about the lithium-metal anode, its x-ray diffraction pattern is weak (because lithium has few electrons) and doesn’t change much during battery cycling (staying as lithium metal). So, they indirectly probed changes in the anode by studying closely related changes in the lithium nickel manganese cobalt oxide (NMC) cathode, whose diffraction pattern is much stronger.
“The cathode serves as a “reporter” for the anode,” explained Khalifah. “If the anode starts to fail, its problems will be mirrored in the cathode because the nearby regions of the cathode will be unable to effectively take up and release lithium ions.”
The XPD beamline played a critical role in the experiment. With their high energy, the x-rays at this beamline can completely penetrate through battery cells, even those a few millimeters thick. The beam’s high intensity and large two-dimensional area detector enabled the scientists to rapidly collect high-quality diffraction data for thousands of points across the battery.enlarge
A state-of-charge map for a single cathode layer extracted from an end-of-life pouch cell after its 199th discharge cycle. The map exhibits three hotspots (numbered circles), each with a state of charge much higher than that in the rest of the cell, indicating localized failure in these locations.
“In this country, NSLS-II is only one of two x-ray synchrotrons suitable for high-energy diffraction studies,” explained Khalifah. “For each point, we got a high-resolution diffraction pattern in about a second, allowing us to map the entire area of the battery in two hours—more than 100 times faster than if the x-rays were generated using a conventional laboratory x-ray source.”
By X Ray Diffraction It Is Found That Nickel Takes
The first quantity they mapped was the state of charge (SOC)—the amount of energy remaining in the battery compared to the energy it had when it was “full”—for the single cathode layer. A 100-percent SOC means the battery is fully charged, having as much energy as it can. With battery usage, this percentage drops. For example, a laptop showing 80-percent power is at an 80-percent SOC. In chemistry terms, SOC corresponds to the lithium content in the cathode, where lithium is reversibly inserted and removed during cycling. As lithium is removed, the cathode’s unit cell volume shrinks. This volume can be easily determined from x-ray diffraction measurements, which are therefore sensitive to the local SOC at each point. Any local regions where performance is degrading will have different SOCs from the rest of the cathode.
The SOC maps revealed three “hotspots,” each a few millimeters in diameter, where the local performance was much worse than that of the rest of the cell. Only a portion of the NMC cathode in the hotspots had trouble cycling; the rest remained synchronized with the cell. This finding suggested the battery capacity loss was due to partial destruction of the liquid electrolyte, as loss of the electrolyte will “freeze” the battery at its current SOC.
Other possible reasons for the battery capacity loss—consumption of the lithium-metal anode or gradual loss of lithium ions or electronic conductivity as degradation products form on the electrode surface—would not lead to the simultaneous presence of active and inactive NMC cathode in the hotspots. Follow-up experiments led by INL team members on smaller battery coin cells designed to intentionally fail through electrolyte depletion exhibited the same behavior as this large pouch cell, confirming the failure mechanism.
“Electrolyte depletion was the failure mechanism most consistent with the synchrotron x-ray and electrochemistry data,” said Khalifah. “In many regions of the cell, we saw the electrolyte was partially depleted, so ion transport became more difficult but not impossible. But in the three hotspots, the electrolyte largely ran out, so cycling became impossible.”
In addition to pinpointing the location of the hotspots where failure was occurring most rapidly, the synchrotron x-ray diffraction studies also revealed why failure was occurring there by providing the amount of NMC present at each position on the cathode. Regions with the worst failure typically had smaller amounts of NMC than the rest of the cell. When less of the NMC cathode is present, that part of the battery charges and discharges more quickly and completely, causing the electrolyte to be consumed more rapidly and accelerating its eventual failure in these regions. Even small reductions in the cathode amount (five percent or less) can accelerate failure. Therefore, improving manufacturing processes to produce more uniform cathodes should lead to longer-lasting batteries.
“This work is a great example of a successful collaboration among BNL, INL, and PNNL by using our different expertise in energy storage,” said Jie Xiao, group leader of PNNL’s battery research program.
“The results from this study and other Battery500 activities clearly show the benefit of using capabilities from across the DOE complex to drive advancement in energy storage technologies,” added Eric Dufek, department manager for INL’s Energy Storage and Advanced Vehicle Department.
In future studies, the team plans to map the changes occurring while the battery charges and discharges.
“In this study, we looked at a single snapshot of the battery near the end of its lifetime,” said Khalifah. “One important result was demonstrating how the technique has sufficient sensitivity that we should be able to apply it to operating batteries. If we can collect diffraction data while the battery cycles, we’ll get a movie of how all the different parts change over time. This information will provide a more complete picture of how failure happens and, ultimately, enable us to design higher-performance batteries.”
This work was supported by the DOE Office of Science and Assistant Secretary for Energy Efficiency and Renewable Energy, DOE Vehicle Technologies Office, through the Advanced Battery Materials Research Program (Battery500 Consortium). NSLS-II is a DOE Office of Science User Facility.
Brookhaven National Laboratory is supported by the U.S. Department of Energy’s Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit https://energy.gov/science.
By X Ray Diffraction It Is Found That Nickel Levels
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2021-18736 INT/EXT Newsroom
Neutron diffraction or elastic neutron scattering is the application of neutron scattering to the determination of the atomic and/or magnetic structure of a material. A sample to be examined is placed in a beam of thermal or coldneutrons to obtain a diffraction pattern that provides information of the structure of the material. The technique is similar to X-ray diffraction but due to their different scattering properties, neutrons and X-rays provide complementary information: X-Rays are suited for superficial analysis, strong x-rays from synchrotron radiation are suited for shallow depths or thin specimens, while neutrons having high penetration depth are suited for bulk samples.
Instrumental and sample requirements
The technique requires a source of neutrons. Neutrons are usually produced in a nuclear reactor or spallation source. At a research reactor, other components are needed, including a crystal monochromator, as well as filters to select the desired neutron wavelength. Some parts of the setup may also be movable. At a spallation source, the time of flight technique is used to sort the energies of the incident neutrons (higher energy neutrons are faster), so no monochromator is needed, but rather a series of aperture elements synchronized to filter neutron pulses with the desired wavelength.
The technique is most commonly performed as powder diffraction, which only requires a polycrystalline powder. Single crystal work is also possible, but the crystals must be much larger than those that are used in single-crystal X-ray crystallography. It is common to use crystals that are about 1 mm3.
The technique also requires a device that can detect the neutrons after they have been scattered.
Summarizing, the main disadvantage to neutron diffraction is the requirement for a nuclear reactor. For single crystal work, the technique requires relatively large crystals, which are usually challenging to grow. The advantages to the technique are many - sensitivity to light atoms, ability to distinguish isotopes, absence of radiation damage, as well as a penetration depth of several cm
Like all quantumparticles, neutrons can exhibit wave phenomena typically associated with light or sound. Diffraction is one of these phenomena; it occurs when waves encounter obstacles whose size is comparable with the wavelength. If the wavelength of a quantum particle is short enough, atoms or their nuclei can serve as diffraction obstacles. When a beam of neutrons emanating from a reactor is slowed and selected properly by their speed, their wavelength lies near one angstrom (0.1 nanometer), the typical separation between atoms in a solid material. Such a beam can then be used to perform a diffraction experiment. Impinging on a crystalline sample, it will scatter under a limited number of well-defined angles, according to the same Bragg's law that describes X-ray diffraction.
By X Ray Diffraction It Is Found That Nickel Is Found
Neutrons and X-rays interact with matter differently. X-rays interact primarily with the electron cloud surrounding each atom. The contribution to the diffracted x-ray intensity is therefore larger for atoms with larger atomic number (Z). On the other hand, neutrons interact directly with the nucleus of the atom, and the contribution to the diffracted intensity depends on each isotope; for example, regular hydrogen and deuterium contribute differently. It is also often the case that light (low Z) atoms contribute strongly to the diffracted intensity, even in the presence of large Z atoms. The scattering length varies from isotope to isotope rather than linearly with the atomic number. An element like vanadium strongly scatters X-rays, but its nuclei hardly scatters neutrons, which is why it is often used as a container material. Non-magnetic neutron diffraction is directly sensitive to the positions of the nuclei of the atoms.
The nuclei of atoms, from which neutrons scatter, are tiny. Furthermore, there is no need for an atomic form factor to describe the shape of the electron cloud of the atom and the scattering power of an atom does not fall off with the scattering angle as it does for X-rays. Diffractograms therefore can show strong, well-defined diffraction peaks even at high angles, particularly if the experiment is done at low temperatures. Many neutron sources are equipped with liquid helium cooling systems that allow data collection at temperatures down to 4.2 K. The superb high angle (i.e. high resolution) information means that the atomic positions in the structure can be determined with high precision. On the other hand, Fourier maps (and to a lesser extent difference Fourier maps) derived from neutron data suffer from series termination errors, sometimes so much that the results are meaningless.
Although neutrons are uncharged, they carry a magnetic moment, and therefore interact with magnetic moments, including those arising from the electron cloud around an atom. Neutron diffraction can therefore reveal the microscopic magnetic structure of a material.
Magnetic scattering does require an atomic form factor as it is caused by the much larger electron cloud around the tiny nucleus. The intensity of the magnetic contribution to the diffraction peaks will therefore decrease towards higher angles.
Neutron diffraction can be used to determine the static structure factor of gases, liquids or amorphous solids. Most experiments, however, aim at the structure of crystalline solids, making neutron diffraction an important tool of crystallography.
Neutron diffraction is closely related to X-ray powder diffraction. In fact, the single crystal version of the technique is less commonly used because currently available neutron sources require relatively large samples and large single crystals are hard or impossible to come by for most materials. Future developments, however, may well change this picture. Because the data is typically a 1D powder diffractogram they are usually processed using Rietveld refinement. In fact the latter found its origin in neutron diffraction (at Petten in the Netherlands) and was later extended for use in X-ray diffraction.
One practical application of elastic neutron scattering/diffraction is that the lattice constant of metals and other crystalline materials can be very accurately measured. Together with an accurately aligned micropositioner a map of the lattice constant through the metal can be derived. This can easily be converted to the stress field experienced by the material. This has been used to analyse stresses in aerospace and automotive components to give just two examples. The high penetration depth permits measuring residual stresses in bulk components as crankshafts, pistons, rails, gears. This technique has led to the development of dedicated stress diffractometers, such as the ENGIN-X instrument at the ISIS neutron source.
By X Ray Diffraction It Is Found That Nickelodeon
Neutron diffraction can also be employed to give insight into the 3D structure any material that diffracts.
Another use is for the determination of the solvation number of ion pairs in electrolytes solutions.
The magnetic scattering effect has been used since the establishment of the neutron diffraction technique to quantify magnetic moments in materials, and study the magnetic dipole orientation and structure. One of the earliest applications of neutron diffraction was in the study of magnetic dipole orientations in antiferromagnetic transition metal oxides such as manganese, iron, nickel, and cobalt oxides. These experiments, first performed by Clifford Shull, were the first to show the existence of the antiferromagnetic arrangement of magnetic dipoles in a material structure. Now, neutron diffraction continues to be used to characterize newly developed magnetic materials.
Hydrogen, null-scattering and contrast variation
Neutron diffraction can be used to establish the structure of low atomic number materials like proteins and surfactants much more easily with lower flux than at a synchrotron radiation source. This is because some low atomic number materials have a higher cross section for neutron interaction than higher atomic weight materials.
One major advantage of neutron diffraction over X-ray diffraction is that the latter is rather insensitive to the presence of hydrogen (H) in a structure, whereas the nuclei 1H and 2H (i.e. Deuterium, D) are strong scatterers for neutrons. The greater scattering power of protons and deuterons means that the position of hydrogen in a crystal and its thermal motions can be determined with greater precision by neutron diffraction. The structures of metal hydride complexes, e.g., Mg2FeH6 have been assessed by neutron diffraction.
The neutron scattering lengths bH = −3.7406(11) fm  and bD = 6.671(4) fm, for H and D respectively, have opposite sign, which allows the technique to distinguish them. In fact there is a particular isotope ratio for which the contribution of the element would cancel, this is called null-scattering.
It is undesirable to work with the relatively high concentration of H in a sample. The scattering intensity by H-nuclei has a large inelastic component, which creates a large continuous background that is more or less independent of scattering angle. The elastic pattern typically consists of sharp Bragg reflections if the sample is crystalline. They tend to drown in the inelastic background. This is even more serious when the technique is used for the study of liquid structure. Nevertheless, by preparing samples with different isotope ratios, it is possible to vary the scattering contrast enough to highlight one element in an otherwise complicated structure. The variation of other elements is possible but usually rather expensive. Hydrogen is inexpensive and particularly interesting, because it plays an exceptionally large role in biochemical structures and is difficult to study structurally in other ways.
The first neutron diffraction experiments were carried out in 1945 by Ernest O. Wollan using the Graphite Reactor at Oak Ridge. He was joined shortly thereafter (June 1946) by Clifford Shull, and together they established the basic principles of the technique, and applied it successfully to many different materials, addressing problems like the structure of ice and the microscopic arrangements of magnetic moments in materials. For this achievement, Shull was awarded one half of the 1994 Nobel Prize in Physics. (Wollan died in 1984). (The other half of the 1994 Nobel Prize for Physics went to Bert Brockhouse for development of the inelastic scattering technique at the Chalk River facility of AECL. This also involved the invention of the triple axis spectrometer). The delay between the achieved work (1946) and the Nobel Prize awarded to Brockhouse and Shull (1994) brings them close to the delay between the invention by Ernst Ruska of the electron microscope (1933) - also in the field of particle optics - and his own Nobel prize (1986). This in turn is near to the record of 55 years between the discoveries of Peyton Rous and his award of the Nobel Prize in 1966.
- ^ abcMeasurement of residual stress in materials using neutrons, IAEA, 2003
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Applied Computational Powder Diffraction Data Analysis
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- Integrated Infrastructure Initiative for Neutron Scattering and Muon Spectroscopy (NMI3) - a European consortium of 18 partner organisations from 12 countries, including all major facilities in the fields of neutron scattering and muon spectroscopy
- Frank Laboratory of Neutron Physics of Joint Institute for Nuclear Research (JINR)