Understanding the Dehydration of Prussian White with X-Ray Diffraction

Introduction

Despite higher performance of lithium-ion batteries, sodium-ion batteries (SIB) have received strong interest within the last few years. (1) The reason being the potentially lower cost of SIBs, related also to the availability of the raw material, as well as the interest in more sustainable energy storage systems. (2) Due to their satisfactory theoretical capacity and especially due to the low cost and abundant metals iron (Fe) and manganese (Mn), Prussian blue analogues are proposed as cathode materials for SIBs. (3) One representative from this group is Prussian White (PW). However, despite the potential advantages, the presence of water in the PW structure significantly degrades its performance. (4) Therefore, to yield best electrochemical properties of PW, the optimal dehydration process needs to be found. In this report, the dehydration of a composite electrode based on a PW material (Na_1.80(5)Fe[Fe(CN)₆]·1.84(3)H₂O) is further investigated. 

Previously, it was shown that the rhombohedral phase, which is favored for electrodes, can be obtained from the dehydration of PW powders at a temperature of 170 °C for 48 hours under dynamic vacuum (10^-2 mbar). (5,6) The question to be addressed here is whether the same conditions hold also true for water-processed electrodes obtained using the pristine PW. To answer this question, in-situ X-ray diffraction was performed using the Automated Multipurpose Powder X-ray Diffractometer XRDynamic 500 from Anton Paar. It is perfectly suited for in-situ diffraction experiments due to its uniquely integrable non-ambient chambers.

References

1. Delmas, Claude. "Sodium and sodium‐ion batteries: 50 years of research."Advanced Energy Materials 8.17 (2018): 1703137.
2. Peters, Jens F., Alexandra Peña Cruz, and Marcel Weil. "Exploring the economic potential of sodium-ion batteries." Batteries 5.1 (2019): 10.
3. Liu, Qiannan, et al. "The cathode choice for commercialization of sodium‐ion batteries: layered transition metal oxides versus Prussian blue analogs." Advanced Functional Materials 30.14 (2020): 1909530.
4. Nielsen, Ida, et al. "Water driven phase transitions in Prussian white cathode materials." Journal of Physics: Energy 4.4 (2022): 044012.
5. Maddar, F. M., et al. "Understanding dehydration of Prussian white: from material to aqueous processed composite electrodes for sodium-ion battery application."Journal of Materials Chemistry A 11.29 (2023): 15778-15791.
6. Wang, Long, et al. "Rhombohedral Prussian white as cathode for rechargeable sodium-ion batteries." Journal of the American Chemical Society 137.7 (2015): 2548-2554.