Speaker:  Dr William Brant, Department of Chemistry, Uppsala University, Sweden

Host:  Associate Professor Siegbert Schmid   [Map]

Abstract:

One of the foremost interests today is in the ability to monitor materials in real time during synthesis or operation. This is particularly true for materials in energy storage applications where subtle changes in the synthesis conditions can induce changes in the structure that have substantial impact on their long term performance. Understanding this impact on performance subsequently requires advances to “online” methods of analysis, which enable simultaneous measurement of key electrochemical performance indicators together with material properties. This talk will start with the advances to in operando methods we have achieved in attempting to squeeze out as much information from a single experiment as possible. Typically, battery and materials scientists will perform diffraction experiments while simultaneously galvanostatically cycling a battery. The electrochemical profile that is obtained acts as a “compositional map” as to the state of charge and consequently the cation content in an active material. However, there is a wealth of information contained in the electrochemical response of a material which can be easily accessed. We have demonstrated this for lithium-sulfur cells by pairing online resistance mapping through the intermittent current interruption technique [1] and in operando diffraction measurements. Thus, the growth and decay of multiple crystalline phases such as Li₂S and polysulfides was correlated directly with variations in internal and diffusion resistance leading to a model describing how electrochemical products form and dissolve within the porous carbon electrode. While this study was focused on the Li-S system, the method would be easily transferred to any electrochemical system involving mass transport and acts as a simple method of identifying and diagnosing sources of failure.

The second part of the talk will focus on our work producing Prussian blue analogues (PBAs) for sodium ion batteries. While there is a strong interest in commercializing PBAs, its development is hampered by the typically non-reproducible nature of the synthesis and subsequently the highly variable performance that is observed. By combining a simple acid decomposition approach followed by sodium enrichment with tracking of key structural features through synthesis we were able to control the vacancy, sodium and water content for Na_xFe[Fe(CN)₆]_1‑y.zH₂O which lead to highly promising electrochemical performance. This synthetic approach has subsequently been improved and successfully scaled up [2]. As an extension to our work demystifying the synthesis of Prussian blue analogues, I will give a brief overview of the commercial state of sodium ion batteries including the current key players, the state of the art and the key technological challenges. An understanding of the challenges materials faced on the road to commercialization can provide inspiration for new commercially relevant research questions.

[1] Lacey, M. J., ChemElectroChem 2017, 4 (8), 1997-2004.

[2] Brant, W. R.; Mogensen, R.; Colbin, S.; Ojwang, D. O.; Schmid, S.; Häggström, L.; Ericsson, T.; Jaworski, A.; Pell, A. J.; Younesi, R., Chem. Mater. 2019, 31 (18), 7203-7211