Effect of crystallinity on the electrochemical performance of nanometer Al-stabilized α-nickel hydroxide

Nanometer Al-stabilized α-Ni(OH)2, synthesized by urea decomposition, was tested to have better crystallinity from Ni(NO3)2·6H2O and Al(NO3)3·9H2O (Sample A) than that from NiSO4·6H2O and Al2(SO4)3·18H2O (Sample B), and more agglomeration was found for the badly crystallized Sample B as shown by TEM. XPS spectra determined that the positively charged part for Sample A and B was [Ni0.78Al0.22(OH)2]0.22+ and [Ni0.95Al0.05(OH)2]0.05+, respectively. TG and DSC showed that the thermal processes of the two samples are different, where Sample B decomposed at a higher temperature. Cyclic voltammetry (CV) test showed that Sample A had better reversibility, and anodic oxidation peak of Sample B disappeared with the increase in scanning rate. Sample A had smaller electrochemical resistance as shown by electrochemical impedance spectroscopy (EIS), and electrode reaction of Sample A is mostly controlled by proton diffusion, while that of Sample B is a mixed controlled electrode process. Sample B also has poorer electrochemical discharge and cycle life performance.