Coprecipitation Temperature Effects of Morphology‐Controlled Nickel Hexacyanoferrate on the Electrochemical Performance in Aqueous Sodium‐Ion Batteries

Abstract Coprecipitation effortlessly fabricated nickel hexacyanoferrate (NiHCF) with outstanding rate capability and stability for aqueous batteries. Citrate‐aided coprecipitation decelerated the crystallization, assembling cubic‐shaped powder based on separation between nucleation and growth. This study revealed that coprecipitation temperature determined the electrochemical performance. With lower temperatures, smaller particles with more water were formed by predominant nucleation, resulting in low crystallinity and capacity of 58 mAh g −1 . Expanded surface area reduced electrode/electrolyte interface charge‐transfer resistance and showed excellent rate capability (79 % of initial capacity at 100 C‐rate). However, poor cyclability was obtained. At elevated temperatures, nuclei growth and dehydration occurred, and thus highly crystalline large particles were formed. In turn, NiHCF delivered excellent capacity of 76 mAh g −1 at 1 C‐rate but exhibited inferior rate performance because of longer diffusional path. Meanwhile, normal coprecipitation at 70 °C induced irregular‐shaped tiny particles, presenting 93 % retention of initial capacity at 100 C‐rate.