Battery technology is one of the keys to a carbon-neutral future for our planet. At Oxford Instruments we support battery research and manufacture with a range of analytical and microscopy techniques across the whole value chain. From elucidating the fundamental electrochemical and materials challenges in battery research to providing tools for the quality control of battery anodes, cathodes and electrolytes, we offer leading-edge solutions from our range of electron microscopy, atomic force microscopy, NMR and deposition and etch equipment as well as scientific cameras.
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The key to successfully addressing research challenges around optimising battery performance, enhancing capacity, maximising power delivery and minimising degradation lies in advanced characterisation techniques that provide quantifiable insights into the materials processes at the nanoscale. Our range of nanoanalytical research tools, ranging from our award-winning Ultim® Extreme EDS system for nanoscale compositional analysis to our in-operando capable Cypher ES atomic force microscope, enable cutting edge insights. Our work with leading research groups in the battery research community and involvement in industry bodies ensures we can support even your most advanced application needs.
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The cathode of a lithium ion battery is made out of a lithium metal oxides derived from manganese (LMO), cobalt (LCO), nickel, iron (LFP), titanium (LTO), or aluminium. More commonly, a combination of three of these metals is used, either nickel manganese cobalt (NMC), Nickel Cobalt Aluminium (NCA). The anode is made out of porous carbon or graphite, although other alternative materials such a Graphene and silicon are being researched to increase battery capacity either as pure materials or as additives to graphite.
When developing the optimum cathode or anode material, a balance between battery cost, energy density, power density, safety and lifespan needs to be struck. Commonly, the stoichiometry is changed for example to improve the energy density by increasing the nickel content in NMC based cathodes. However, changes in composition also change the structural and electrical properties of the material. Electron microscopy is used to conclusively link these structure-property relationships. By imaging samples of anode and cathode materials at high enough resolution to detect changes that occur over the battery lifetime as well as to form a detailed view of the homogeneity of the material, the researcher can relate structural changes to important battery properties such as energy density, power density, safety and lifespan.
Materials used in lithium ion batteries are often very sensitive to high electron beam doses and Oxford Instruments therefore supply a range of extremely sensitive detector that allow compositional and structural measurements at minimal electron beam doses.
Our range of Ultim Max and Ultim Extreme EDS detectors and our Symmetry EBSD detector are used by leading research groups to:
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In lithium-ion batteries the cathode and anode are separated by a separator membrane which contains the usually liquid electrolyte. Alternatively, solid electrolytes are being researched which could offer meaningful improvements in safety and energy density as well as offer cost savings.
Liquid electrolytes
The most commonly used liquid electrolyte is lithium-salt solution (LiPF6 or LiBF4) with binders and additives added to reduce gassing and increase the viscosity. Liquid electrolytes can degraded and outgas during the charge and discharge process which can lead to swelling of the battery and for some reaction products can also lead to corrosion of the battery. For example, hydrofluoric acid can be formed as a breakdown product.
Oxford Instruments cryogen-free X-Pulse NMR system is the only benchtop NMR that can measure all components in a single system (1H, 13C, 19F, 7Li, 31P, 11B). It also reliably identifies and quantifies breakdown products such as HF and LiF and measure diffusion coefficients.
Figure 1 (right): The X-pulse benchtop NMR system comes with pulsed field gradients as standard. This allows measurement of self diffusion, like those shown, to understand key physical properties of the electrolyte, including the conductivity and the ion transference.
Solid electrolytes
A number of different materials are being researched as candidates for solid electrolytes in Li-ion batteries which are safer but also potentially higher energy density than existing batteries by enabling the use of metallic lithium anodes. However, the conductivity of Li ions is usually lower in solid state electrolytes than in their liquid counterparts. Imaging the Li distribution in the SEM can provide vital information about the materials structure as well as any detrimental dendrite formation. In combination with conductivity measurements it enables new research aiming to improve the performance of solid-state electrolytes and eventually enable an all solid-state battery to be built. Ultim Extreme is the only EDS detector that enables the detection of lithium X-rays in an SEM at low enough beam currents to not significantly alter the sample.
Figure 2: (Left) Solid State Garnet Electrolyte before acquisition; (middle) X-ray map
acquired at 2.5kV with Ultim Extreme at 100pA beam current – three different Li containing
phases identified; (right) Same area after acquisition with no observable damage
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Probing the battery structure and properties during operation can give important insights that could be missed when looking at components post-mortem. Our Cypher AFM can be customised for operation in glove boxes. It can also be fitted with an electrochemical cell that enables direct imaging of the electrode surfaces during battery operation. This enables a detailed study of SEI layer formation and stability.
Figure 1: LiO2 battery testing with a Cypher ES in an argon glovebox. (A) Photo of the Cypher ES integrated into an Ar-filled Mbraun glovebox; (B) Schematic of the
battery cell and sealed sample chamber used in these experiments. Pure O2 flows into the AFM but does not escape into the glovebox atmosphere due to the hermetic seal of the sample chamber.
We offer a range of imaging modes on the AFM which can probe structural as well as functional properties in battery materials. Electrochemical strain microscopy (ESM) for example is a novel scanning probe microscopy (SPM) technique for the Cypher™ Atomic Force Microscopes (AFM) that is capable of probing electrochemical reactivity and ionic flows in solids with unprecedented resolution. ESM is based on detecting the strain response of a material to an applied electric field through a blocking or electrochemically active SPM tip. The insertion and extraction of Li-ions in Li-battery electrodes produce large volume changes. The sensitivity of a platform such as the Cypher AFM allows for detection of~1 picometer surface displacements, which allows a theoretical detection limit of approximately 10% changes in lithiation state within one unit cell (i.e., elementary volume of material) for materials such as LiCoO2.
An applied bias to the tip induces ionic motion in the sample and the resulting surface deformation is detected by the SPM probe and electronics, generating an image that maps the ionic motion at the nanoscale. The dependence of the c-lattice parameter (perpendicular to layers) on lithiation in prototypical LixCoO2 cathode material. In the operation region of Li-ion batteries (from x = 1 to x=0.5), the lattice parameter changes linearly with x by 40 pm.
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A major factor for the adoption of electric vehicles is the charging time, especially as the range of even the most advanced electric vehicles can currently not match the range of most cars using an internal combustion engine. More efficient power electronics are one of the key technologies. Silicon Carbide based devices are set to significantly disrupt the fast charging market, allowing faster and more efficient charging.
Oxford Instruments has a deep understanding of how to make the most optimised SiC devices through its process solutions such as atomic layer deposition, plasma etching and plasma deposition.
Plasma processes play an important role in several processing steps of a SiC MOSFET device:
Manufacturers of lithium-ion batteries and their suppliers face challenging conditions where relatively new technologies need to be scaled up quickly for mass production. With customers in the automotive and electronics industry requiring longer lifetimes, higher capacity, lighter weight and lower cost, the characterisation of raw materials as well as battery components and finished goods play a major role in delivering a high quality product to customers. At Oxford Instruments we provide solutions for different parts of the value chain reaching from the mining of raw materials to the quality control of components, all the way to the failure analysis of batteries.
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The materials used in the production of Li-ion batteries must be of high purity in order for the batteries made from them to have the expected performance and lifetime and also to prevent dangerous failures caused by metallic particles penetrating isolating barriers. Quality control and monitoring of materials throughout the manufacturing process is crucial as even very small amounts of contaminants can have catastrophic consequences.
AZtecBattery provides a fully automated solution for identifying and characterising contaminants in powder materials. Understanding the sources of contamination is the first step towards eliminating them and ensuring the quality of the manufactured product.
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NMR spectra give a detailed view of the chemical species present in the electrolyte materials. Being inherently quantitative, our X-Pulse benchtop NMR is ideally suited for the rapid analysis of LiPF6 or LiBF4 and the measurement of the purity of the precursor salts. It operates cryogen-free and is the only benchtop NMR system that can detect all relevant components in a single system: 1H, 13C, 19F, 7Li, 31P, 11B
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The quality and performance of batteries depend crucially on the cathode and anode materials used. For example, graphite anodes are often laced with Silicon particles as the gravimetric capacity of Silicon is ten times higher than that of Graphite. However, the difference in volume expansion between the two materials can lead to structural defects, which can negatively affect the battery lifetime. Also, silicon additives can come from a variety of sources and contain traces of other elements that affect battery performance. Figure 1 shows an EDS map acquired in a scanning electron microscope of an anode that contains mainly graphite (here in red) but also a certain percentage of Silicon particles. A more detailed analysis compositional analysis of one of the Silicon particles reveals a significant amount of other elements present in larger amount than in the dominant Graphite material, such as Oxygen and Tin but also traces of Zirconium.
| C (Wt%) | Si (Wt%) | O (Wt%) | Sn (Wt%) | Zr (Wt%) | F (Wt%) | Na (Wt%) | |
| Si NP | 41.85 | 38.94 | 10.68 | 7.28 | 0.94 | 0.18 | 0.12 |
| Graphite | 99.30 | 0.05 | 0.33 | 0.17 | 0.16 |
In cathodes the spatial distribution of Cobalt and Nickel, as well as the total chemical composition of the particles, can be of interest as interface effects on the surface of the particles are critically important to the battery lifetime and degradation. In Figure 2 we show a high-resolution EDS map of an NCA cathode that clearly shows Co present as a shell on the surface of the particles which was confirmed by using a quantitative line scan plotting the nickel and cobalt content.
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Optimising battery electrolyte performance & quality with benchtop NMR
Improving the performance and reliability of next generation batteries relies on optimising the current carrying electrolyte solutions inside them. In this interactive webinar, our applications team highlight why benchtop NMR spectroscopy is so significant from raw materials checking, right through the R&D cycle to quality control in battery manufacturing.
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Improving Li-Ion battery performance through materials characterisation
Researchers face significant challenges in improving the performance of Lithium ion batteries. This webcast will explore how material characterisation is key to balancing the essential battery qualities of energy density, power density, cost, safety and lifetime.
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Powering The Future Through Nano-Characterisation
The presence of impurities and contaminants in the material used in the production of Li-ion batteries can have catastrophic impacts on the finished battery products with incidents of such failures having been widely reported. As such, monitoring of the quality and cleanliness of materials throughout the production process is essential if contaminants are to be found and their sources controlled.
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