Ball Milling-Enabled Fe to Fe Redox Reaction in Prussian Blue Materials for Long-Life Aqueous Sodium-Ion Batteries.

Aqueous Na-ion batteries using Prussian blue materials have inherent advantages in safety, material sustainability, and economic cost. However, it is challenging to obtain long-term cycling stability because many redox reactions have poor intrinsic stability in water. Here, we demonstrate reversible Fe to Fe redox reaction of Prussian blue electrodes cycled in a 17 m NaClO water-in-salt electrolyte.