Alpha nickel hydroxide electrodes improve aqueous rechargeable batteries capacity

Nickel hydroxide electrode materials have been improved for the use in Ni-based rechargeable batteries such as Ni-H2, NiMH, NiCd, NiFe, and NiZn batteries. A stabilized α-phase Ni1-xAlx(OH)2, synthesized using wet chemical coprecipitation methods while controlling pH accurately followed by hydrothermal treatments at 165 °C, is reported. Variations in synthetic routes, dopants and morphology had strong influence on the electrochemical performance. Morphological control, crystallinity and surface modification by Co(OH)2 were important for the better performance. Conventional battery grade β-Ni(OH)2 is usually made of a spherical particles, but we find that circular shaped particles can be advantageous. Hydrothermal treatments increase sample crystallinity and discharge capacity. A hydrothermal treated Ni0.8Al0.2(OH)2-LDH sample reaches a discharge capacity of 368 mAh g−1 and a corresponding Ni0.9Al0.1(OH)2 reaches 405 mAh g−1. Both have a circular-like morphology and the later shows a tap density of 1.52 g cm−3 and volumetric energy density of 531 mAh cm−3. Only a modest Co(OH)2 surface coating is needed to reduce the polarization behavior, increase the redox reaction reversibility and electrode kinetics via formation of CoOOH species after electrochemical oxidation.