A correlative workflow to probe electrode cross-talk in representative sodium-ion systems through advanced synchrotron cell design Connor Wright 1 , Huw Shiel 1 , Zhenyu (Johny) Guo 2 , Thokozile Kathyola 3 , Miguel Gomez- Gonzalez 3 , Magda Titirici 2 , Mary Ryan 1 1 Department of Materials, Imperial College London, UK, 2 Chemical Engineering Department, Imperial College London, UK, 3 Diamond Light Source, Harwell Science and Innovation Campus, Didcot, UK Electrode cross-talk is an understudied mechanism that causes cell degradation and capacity loss. In real-world applications, cells or particles within the cathode can be routinely and randomly pushed outside design voltages due to ageing or abuse [1]. These extreme potentials can be responsible for the dissolution of transition metals, which can travel from the cathode and integrate into the forming SEI at the anode, further depleting active shuttling ions [2]. The variety of techniques available at synchrotron facilities makes them ideal for probing fundamental electrochemical evolutions of both positive and negative electrode materials. However, unexpectedly, fundamental research into the nano- and micro-scale processes that cause cross-talk remains very challenging when observing a representative 2-electrode system, due to: Beamline constraints:Beamlines have requirements necessary to yield a good signal (e.g, sample preparation or cell architecture related). Successful applicants commonly bring their own specially designed cell(s) in battery research. In reality, the beamline has likely already hosted similar experiments. This adds uncertainty around the comparability of certain results, especially when these are said to be collected ‘ in situ ’ (under conditions relevant to practical operation) or ‘ operando ’ (conditions directly representing the real-world working of the sample; often time-resolved). Lack of reference is 2-electrode cells: By design, these have no reference by which to measure absolute values of potential. Whilst mitigated by using 3-electrode cells, these systems offer their own problems related to masking potentially significant side reactions by introducing a huge excess of sodium ions, thus limiting the extent to which the experiment can be labelled ‘ in situ ’ or ‘ operando ’. Here, we present a novel cell design developed specifically to study both battery electrodes in practically relevant conditions. This new “sealed system” cell was first used at Diamond in July 2023 to study an archetypal Na-ion cathode, NVP. Allowing X-ray penetration from two different sides, this design enables the study of anodic SEI formation and cathodic transition metal dissolution via soft X-ray NEXAFS (B07) and hard X-ray XANES (I14), respectively. Most importantly, each electrode can be investigated in the same cell and in identical environments (excluding beam damage-related changes), as the cell's modular design does not need any significant modification between experiments. To conclude, it is thought that this type of multi-purpose, cross-beamline approach to cell design will allow for more systematic investigation into the fundamental electrochemical processes that cause cross-talk degradation. By studying both electrodes in the exact same environment, the representative insights gained can be better used to rationally design against electrode cross-talk in the future. References 1. Wang, Z., Hong, J., Liu, P. & Zhang, L. (2017) Applied energy . 196, 289–302. 2. Gilbert, J.A., Shkrob, I.A. & Abraham, D.P. (2017) Journal of the Electrochemical Society . 164 (2), A389.
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