Reducing nickel-cobalt hydroxide crystallization for optimal nickel-zinc battery performance

Electroactive materials with low crystallization are particularly promising for energy storage owing to additional grain boundaries and ion diffusion channels, but their applications are limited by the consensus that crystalline samples have higher stability in most applications. Here, we developed a solvothermal method for synthesizing low-crystallized nickel-cobalt hydroxide (NiCo−OH−L) using N-methylpyrrolidone and water-mixed solvents. For nickel-zinc battery (NZB) applications, the NiCo−OH−L was found to have comparable cycling stability to its high-crystallized counterpart. However, it showed an increased capacity and capacity retention in the current region of 1–50 A g−1. The superior performance was due to the low-crystallized structure, which has a large specific surface area and reduced charge transfer resistance. Furthermore, the cobalt constitution in the NiCo−OH−L improves its rate performance and cycling stability. As a result, the NiCo−OH−L had a capacity of 238.9 mA h g−1 at 1 A g−1 and maintained 116.4 mA h g−1 at 50 A g−1, indicating both high-capacity and high-rate performances. More significantly, the NiCo−OH−L-assembled NZB exhibited consistent performance under different currents and cycling cycles.