Innovative battery characterisation method brings benefits to industry partners
Researchers at WMG, University of Warwick, have pioneered X-ray methods to routinely study industrially relevant pilot-line-built pouch cells during operation in laboratory settings, an achievement previously not feasible. This novel method is advancing the fundamental understanding of battery degradation mechanisms and accelerating the research process. Leveraging the expertise cultivated through the Degradation project, the method is being used by industry partners to improve battery performance, demonstrating significant benefits for UK industry.
The challenges of studying batteries in operation
Studying lithium-ion batteries during operation has been possible using X-rays since the late 1970s. This technique allows scientists to observe changes in the internal structure of the battery’s materials, which helps them understand how batteries function. Specifically, it lets researchers see how lithium ions, which carry the charge, move in and out of the battery’s electrode materials. This movement, known as intercalation, is what makes lithium-ion batteries so effective at storing large amounts of energy time and time again after recharge.
However, in order to study battery cells while they are charging and discharging, significant modifications have needed to be made to the cells, such as adding a window material that X-rays can pass through. While these modifications allow for the collection of data, they often compromise the electrochemical performance of the cell, they often operate far from realistic conditions and they are not representative of cells used by industry. This has created a gap between academic research and practical industrial application.
Additionally, most successful studies on commercially relevant battery cells during operation have relied on the use of advanced facilities like neutron and synchrotron beamlines. These studies typically use commercial cylindrical cells, limiting researchers’ control over cell design and using the technique in new materials development. Access to these national facilities is also limited and can delay the research process.
Professor Louis Piper and Dr Ashok Menon, WMG, University of Warwick
A new method brings new understanding
As part of the Faraday Institution Degradation and FutureCat projects, a team at WMG, University of Warwick, led by Professor Louis Piper, has successfully developed a groundbreaking in-house operando X-ray method for studying full format A7 (7.5 cm x 10.5 cm) single layer pouch cells. This novel approach allows the study of industrially relevant cells without adaption (i.e., no windows), using both X-ray absorption spectroscopy and diffraction. Furthermore, the method enables cycling at industry relevant charge/discharge rates and for long duration studies, which is crucial for understanding how cell performance changes over time and identifying degradation mechanisms. This capability allows for the investigation of cells manufactured on WMG’s pilot line, incorporating new cathode or anode materials or innovative cell architectures under realistic conditions at various stages of life.
One significant advantage of this new method is its in-house capability within a university laboratory. This approach gives researchers greatly increased access, enabling the analysis of multiple cells and thus improving the statistical robustness of experiments. It also accelerates materials development, as researchers are no longer solely dependent on limited beam time and access to central facilities. The method is chemistry-agnostic and can be applied to lithium-ion or next generation technologies like sodium-ion and lithium-sulfur.
Shining light on degradation mechanisms for automotive OEMs
Dr Sylwia Walus, Research Programme Manager at the Faraday Institution, explains the value of the method and access to research expertise from the Degradation project team for automotive OEMs:
Many OEMs are investing heavily in their in-house R&D capabilities so they can engage with battery manufacturers at a fundamental level about the underlying science. This allows them to set R&D directions and act as informed customers when cell manufacturers propose changes to cell design. The method developed at Warwick is highly relevant to industry. Insights gleaned from using this technique are already being incorporated into OEM-battery manufacturer discussions.”
In its first five years of existence, the Faraday Institution’s Degradation project became a centre of excellence in understanding the degradation mechanisms of industry-standard NMC811-graphite batteries (with a lithium nickel manganese cobalt oxide cathode). Researchers are now applying their knowledge and new characterisation techniques, including WMG’s new method, to investigate the degradation of other industry-relevant systems. For example, the project is expanding its research to include other cathodes such as manganese-doped lithium iron phosphate, and anodes such as silicon and even ‘anode-free’ architectures.
A schematic of the characterisation techniques used by the Faraday Institution degradation project.
Sylwia continues:
Many industry organisations are using their in-house capabilities to investigate how factors such as particle sizes, particle coating processes, and calendaring parameters affect cell performance. The new WMG method adds another tool to researchers’ toolkit to enhance the understanding of how electrode structure impacts the battery performance characteristics that drivers of EVs care about. The strength of the Degradation consortium lies in its ability to tackle these engineering challenges while also delving deeply into the science behind the behaviour of these systems. Experts in more than 12 characterisation techniques from nine universities are working together to significantly advance the understanding of degradation mechanisms, directly benefiting industry organisations.”
As an example of how the new method is being used, single crystal NMC811-graphite A7 pouch cells constructed on the WMG pilot line were investigated while being cycled 100 times under harsh conditions. The study demonstrated that battery degradation in this case primarily stems from a restructuring of the cathode’s surface, which slows lithium-ion transport. After cycling, the cells were deconstructed and examined under electron and X-ray microscopy, revealing that the single crystal cathode particles can withstand severe structural changes without cracking. Researchers identified that cathode surface passivation could prevent this type of degradation and prolong cycle life.
Spreading the word into academia, industry and the general public
Initial studies using WMG’s new method have been published in PRX Energy. Due to the overwhelming support of the reviewers and significant interest in the paper (evident from high download rates, and social media engagement), the article was highlighted by editorial staff in an APS Physics article.
The new method has already been adopted in projects with three UK and international industry partners, and is planned for use with several further companies.
One industry partner is using this tool as a method for identifying the degradation mechanisms associated with capacity fade and cell impedance increase. Real-time diagnostics have helped pinpoint pathways to mitigate degradation and improve cycle life.
The team’s facility has been showcased on the Royal Institution‘s YouTube channel.
Royal Institution YouTube video on Building Better Batteries with professor Louis Piper.
Published in October 2024.