The baseline of Prussian White: exploring the electrochemical and physical properties for thick structured electrodes Halima Khanom 1 , Carl Reynolds 1,2 , Brij Kishore 1 , Lin Chen 1,3 , Emma Kendrick 1,2,3 1 University of Birmingham, UK, 2 The Faraday Institution, UK, 3 SIMBA, UK Currently, Sodium-ion batteries (SIB) are one of the main competitors against Li-ion batteries, due to their similar chemistries. Although there is an atomic size discrepancy between both elements, SIB can be tuned for specific uses that Lithium may not be essential for i.e. stationary storage. Moving towards Na-ion materials, overcomes the sustainability issues related to Lithium, as sodium is more abundant and safer. Here, the development of Prussian White (PW) water-based inks for thick, structured electrodes will be presented. Thicker electrodes (>100 µm) have the potential to have both high power and higher energy, however there is a trade-off between both properties. When increasing the thickness of a standard one-dimensional electrode this will lengthen the ionic pathways, limiting our rate of ionic diffusion. To overcome these restraints, we can introduce a 3D architecture within the electrode microstructure to maintain the favourable, short ionic pathways; which can be done by 3D printing, spray coating or templating. The material itself is a sodium iron hexacyanoferrate crystal (NaxFe[Fe(CN)6], where x<1.92), which has the potential to be used for thick electrodes, due to its low cost and comparable capacity with other Li-ion materials. Moreover, the PW exhibits a distinct phase change which can be visualised through the electrochemical performance of the cells. From initial research, the moisture sensitivity of PW was observed clearly in the electrochemistry where sloping voltages and poor cell capacities were seen. Therefore, an effective drying process was developed to prevent the leaching of water molecules, thus allowing the full usage of the PW and achieving the theoretical capacity of 160 mAh/g. 1 PW was examined via different mass loadings from 1-3 mAh/cm 2 , where we successfully demonstrated how thicker electrodes can provide a comparable cell capacity throughout, as demonstrated by our electrochemical data. However, the limitations of thicker electrodes were detected in the rate test data, where the PW experiences no capacity retention at high C rates, due to the limits of the elongated diffusion pathways. PW is also being investigated here to see whether PW has potential to be 3D printed through an extrusion process to create our desired structured electrodes. To understand how effectively an electrode ink will be printed, the rheology properties of the ink is also characterised here. The different parameters to achieve a high viscous ink will also be discussed to allow the fabrication of thick, structured PW electrodes. These specialised fabrication methods can be used for other materials and has the potential to demonstrate structured electrodes through 3D printing to produce a cell with both high energy and power. References 1. L. Wang, J. Song, R. Qiao, L. A. Wray, M. A. Hossain, Y.-D. Chuang, W. Yang, Y. Lu, D. Evans, J.-J. Lee, S. Vail, X. Zhao, M. Nishijima, S. Kakimoto and J. B. Goodenough, J. Am. Chem. Soc. , 2015, 137 , 2548–2554.
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