Prussian blue is a deep blue pigment with the chemical formula Fe₄[Fe(CN)₆]₃, and in battery applications, it's used in the form of a compound known as "Prussian blue analogs" or "Prussian blue derivatives." It is used in the cathodes of sodium-ion batteries, where its unique structure provides several advantages. The stability, combined with the cost-effectiveness of the materials, makes Prussian Blue a promising option for large-scale energy storage systems, such as grid storage, where long battery life and low costs are critical. Additionally, while still in development, Prussian Blue-based batteries could eventually find applications in electric vehicles, particularly in lower-cost models.  

‍