Understanding Interfacial Phenomena in Battery Systems—Addressing the Measurement Challenges

In the quest to reach Net Zero targets, the development of improved energy storage systems plays a key a role. However, Lithium-ion batteries suffer from stability issues that lead to capacity loss with time and use. Huge research efforts are being dedicated to improving the performance of existing lithium-ion systems, as well as pursuing new battery chemistries as viable alternatives. This challenge requires improved understanding of how battery systems work, as well as why their performance degrades with use, from the macroscale down to the nanoscale.<br/><br/>With most reactions occurring at surfaces and interfaces during battery operation, techniques that allow these surfaces to be characterised for both in operando and post-mortem settings are critical. However, the measurement of such complex and heterogeneous systems is not trivial and still lacks standards and guidelines for data collection and interpretation, which can lead to a lack of trust in the data. Without reliable materials characterisation data, accurate conclusions cannot be made and therefore the research and development of improved batteries will be hindered.<br/><br/>In this talk, I will demonstrate the measurement challenges for key post-mortem surface analysis techniques, namely focused ion beam scanning electron microscopy (FIB-SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and time-of-flight secondary ion mass spectrometry (ToF-SIMS). I will describe the current best practice for these techniques and, specifically, I will provide key recommendations to improve the reproducibility of measurements, to enable both academia and industry to better understand the degradation mechanisms for these electrodes and aid in the development of better lithium-ion batteries.<br/><br/>Furthermore, I will show examples of typically used spectroscopy techniques (Fourier transform infrared and Raman spectroscopy) when applied to studying new electrolytes for use in magnesium battery applications in operando, during electrochemical cycling. The development and validation of “minimally-invasive” test protocols for in operando testing allows direct measurement of the material changes under realistic operating conditions, rather than ex-situ after battery teardown. To this end, the changes in the electrolyte during electrochemical cycling can be studied, which we have demonstrated can be used to study the mechanisms of plating and stripping.<br/><br/>Addressing the metrology challenges in the analysis of battery electrodes both in operando and ex-situ is key for the battery community and will ultimately lead to the improvement of existing battery systems and enable the transition to post lithium-ion technologies.