The working electrodes consisted of 70 wt% KFeFe-PBA sample, 20 wt% Super P, and 10 wt% poly(vinylidene fluoride) (PVdF). This mixture was prepared into a slurry with an optimised amount of 1-methyl-2-pyrrolidone (NMP). The slurry was coated on an aluminum foil using a doctor blade and then vacuum dried at 120°C overnight.