An interview with Ning Yang, exploring the use of lithium-ion batteries in wider applications and assesing battery performance with X-Ray Diffraction, conducted by Alina Shrourou, BSc.
What features must be present in lithium-ion batteries for them to be suitable for automotive applications?
Batteries in the automotive industry must be very durable and should have a long cycle time. This means that we can cycle the battery for a long time without losing the capacity. The power inevitably will be lost to a certain extent, but the less loss there is, the better the battery. That’s the first important feature.
Secondly, it is important for these large capacity batteries to be inexpensive. When batteries are very costly, people will not be able to afford electric vehicles and so the vehicles will not be popular.
The final reasons are in relation to battery safety and sustainability. Battery safety for the automotive industry is increasingly important due to more electric vehicles being on the roads. The batteries should also be easy to make and easily recyclable.
What are the challenges associated with improving batteries for automotive and power grid applications?
Batteries contain liquid electrolytes which makes them very prone to breaking. In the case of Li-ion batteries, lithium is a very active metal and so the biggest challenges for battery manufacturers is to improve the safety. This is the first priority challenge for automotive and power grid applications of Li-ion batteries.
Please highlight the importance of in operando observations for researching cathode materials.
In operando observations for researching battery materials are extremely important, as they provide information about the cathode and anode materials while the battery is being used.
Previously, researchers categorized battery materials by performing ex situ experiments. However, with these types of studies, we cannot observe the materials structure at working status or the working structure of the materials. The operando observations open a new door for material research. This way, you can see exactly how the material structure associates with the properties required for that material when it’s in use. For example, researchers can see the detailed structure of the materials at a certain voltage, or at a certain working status of the battery materials.
In operando experiments provide a continuous observation. It's not like you have to break the battery and take the material out to measure it, you can actually observe the materials when the battery's in function.
How is the performance of a lithium ion battery electrode material determined using XRD?
We are using XRD to categorize the structure of the material which includes the crystal structure and the microstructure.
We can study the crystal structure with XRD to determine the ion positions and functionality. For example, if the lithium was trapped at the nickel site of the materials, this kind of lithium hardly performs during battery recycling, which results in losing the capacities of the battery. Therefore, we must calculate how many lithium ions were trapped inside the nickel site and this is something we can determine by XRD analysis.
One major microstructure of materials relates to the crystal size, which can be measured using XRD. By doing this, we can relate the performance of the lithium-ion battery and its microstructure and optimize it for the best performance.
Please outline the use and features of the D8 ADVANCE for in operando characterization of li-ion batteries using XRD.
The D8 ADVANCE is a very popular XRD instrument made by Bruker. Researchers use the D8 ADVANCE to characterize the battery materials for the following 3 reasons. Firstly, the D8 ADVANCE is a very accurate instrument to measure the powder diffraction patterns, and the angular accuracy is very high, so we can get a very accurate XRD spectrum and we can get a precise calculation of the structure.
Secondly, the detector in the D8 ADVANCE gives you the best quality of data acquired from battery materials. Battery materials usually contain iron, nickel, cobalt and even manganese, and those kinds of elements will generate a fluorescence signal. The D8 ADVANCE is equipped with a very good detector that can greatly lower the fluorescence background. It's called an energy dispersive PSD detector, and it can remove all of the fluorescence background and even the K-beta signal without using a nickel filter. This will give you a true XRD pattern with very low background and high intensity.
Thirdly, the D8 ADVANCE can be equipped with powerful software called TOPAS, which offers the most accurate structural refinement of the materials. TOPAS can batch-process the in situ data with a single click and put the results data into a spreadsheet.
Please describe the methodology behind diffraction data collection using the D8 ADVANCE.
The D8 ADVANCE uses the most popular powder XRD method, known as Bragg-Brentano geometry, to acquire data from the battery materials. This provides the best quality of diffraction data. It can be also configured into a transmission mode with short wavelength for the data collection of punch cell and the final battery pack.
How and why are diffraction patterns different depending on whether a battery is charging or discharging?
Diffraction patterns change due to the change of the structure of the materials. The lithium ion moves during the charge and discharge of the battery. If we look inside the battery materials, when the battery's on charge, the lithium ion will move out of the cathode materials into the anode materials, meaning that one material will lose lithium and one material will gain lithium.
During charging, the cathode material loses the lithium and therefore the structural parameters of the materials change. This will result in a very clear change on the peak position and intensities of the diffraction pattern. This is also true for anode materials.
How does the EIGER 2R 500K complement the D8 ADVANCE in collecting in situ XRD data of electrode performance?
The EIGER 2R 500K is a very new detector that has been implemented in our D8 diffractometer family. It’s a large, single photon counting detector with high sensitivity. Due to the larger detector size, we can gather the data much faster. If you want to charge an electric vehicle, you don't want to wait for a day; you want to be able to charge it for the minimum amount of time with maximum output. Therefore, this quick data collection is important for battery research, as we try to charge and discharge the battery increasingly faster. For this reason, the EIGER 2R 500K will be very important for those customers who need a faster instrument to characterize the structure change and perform in situ research of the materials.
Are there any other types of batteries that XRD can be used to characterize?
XRD is a technology that can characterize any structure change. Right now, most battery manufacturers use lithium as an ion carrier. However, in the future, they will be using all sorts of different batteries, for example, sodium.
Sodium batteries are getting more popular in research because sodium is more abundant on Earth, and so these types of batteries could support our cost effective and sustainability needs.
Overall, I believe that XRD is a technology that allows us to better understand battery function and the mechanisms involved. XRD is very important not only for research but also for battery production.
About Dr Ning Yang
After completing a PhD in Materials Science & Engineering at Iowa State University, Ning went on to be a Postdoctoral Associate, focusing on synchrotron x-ray powder and single crystal diffraction research on materials.
Ning has been part of Bruker since 2006, where he has held the role of XRD Application Scientist and Application Team Manager for the last 9 years.
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