OPTIMIZING PROCESSING AND SYNTHESIS OF PRUSSIAN BLUE ANALOGS FOR SODIUM-ION BATTERIES

Abstract

Electric vehicles and energy storage systems are major drivers in the quest to accelerate the transition towards a sustainable future. However, the incumbent lithium-ion battery technology that they rely on, might be a weakness in the future because of the mismatch between rising demands and supply of scarce and expensive metals like cobalt, lithium, nickel, and copper that Li-ion cells heavily employ. To overcome this, more sustainable chemistries, i.e., sodium- and potassium-ion cells, are being investigated with the goal of incorporating more earth-abundant metals into the composition of the electrodes and establishing more sustainable supply chains. Sodium-ion cells employing manganese hexacyanoferrate (MnHCF) as the positive electrode are of particular interest because this material can be tailored to be composed of mostly earth-abundant elements like iron and manganese. However, their cycle life is not yet sufficient for grid energy storage, and they suffer from undesirable water uptake that can be detrimental to cell performance if released into the organic electrolyte in significant amounts.

This work focuses on setting up synthesis and evaluation standards for Prussian Blue Analogs as positive electrode materials in sodium-ion cells. Three distinct synthesis routes were explored: co-precipitation, hydrothermal, and mechanochemical synthesis.Optimization of synthesis and processing conditions yielded high specific energy materials that were competitive with commercial lithium iron phosphate on a Wh/kg basis. A reduction in the water content of Prussian Blue Analogs was achieved through careful vacuum drying. Overall, this work should help the future development and commercialization of sustainable cells employing Prussian Blue Analogs.