Surface Modification of Prussian White Cathode to Improve Air and Cycling Stability in Sodium-Ion Batteries

Abstract

Sodium (Na)-ion batteries (NIBs) are promising alternatives to lithium-ion batteries, because they use abundant and inexpensive sodium-based raw materials and have similar manufacturing processes to lithium-ion batteries. Prussian White (PW) cathodes in NIBs rival the lithium iron phosphate cathode for lithium-ion batteries; they have high energy density, tunable redox potentials, and they are inexpensive and easy to synthesize. Despite their benefits, PW materials are hygroscopic and suffer structural instability associated with the adsorption of water. Additionally, side reactions with and dissolution into the electrolyte can cause PW cathode degradation during cycling. While the synthesis of PW for NIBs often requires acidic conditions that evolve HCN, we have developed a neutral aqueous synthesis method for an iron-manganese based PW cathode that uses non-hazardous, inexpensive materials. Furthermore, surface modifications including metallic doping were studied to better understand the impact that surface stabilization has on the electrochemical behavior of PW cathodes. In this study, we have employed characterization techniques including X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, inductively coupled plasma-atomic emission spectrometry, and x-ray photoelectron spectroscopy, as well as extensive electrochemical testing to study how our synthesis and post-synthesis modifications impact the performance of PW cathodes. We show that our PW cathodes have improved stability against moisture and improved cycling stability.