Structural and electrochemical performance of Al-substituted β-Ni(OH)2 nanosheets electrodes for nickel metal hydride battery

• Al-substituted β-Ni(OH)2 were prepared by a simple template-free growth method.
• The effect of Al contents on the electrochemical performances was investigated.
• The specific discharge capacity was greatly enhanced by the addition of Al.

Al-substituted β-Ni(OH)2 nanosheets are directly grown on nickel foam by a simple template-free growth process. Their microstructure and surface morphology are studied by X-ray diffraction spectroscopy, scanning electron microscopy and transmission electron microscopy. The SEM and TEM images show changes in the microstructure of β-Ni(OH)2 by the addition of Al. The XRD results show that the α-phase Ni(OH)2 appeared in Al-substituted Ni(OH)2 electrodes. The effects of Al content on the electrochemical behaviors are investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The results demonstrate that the 7 mol% of Al in Ni(OH)2 has better electrochemical performance, such as better reaction reversibility, higher proton diffusion coefficient, lower electrochemical impedance, higher specific capacity, and better cyclic stability. The as-prepared 7%-Al-Ni(OH)2 electrode exhibits a specific discharge capacity of 324.5 mAh g−1 at 0.2 C, 220.6 mAh g−1 at 10 C, and 198.6 mAh g−1 at 30 C. The specific capacity loss is less than 8% after 200 charge/discharge cycles at 0.2 C and with columbic efficiency higher than 90%. This work suggests that the as-prepared 7%-Al-Ni(OH)2 electrode has a promising future as higher charging/discharging rate materials for nickel metal hydride power battery.