Comparative structural and electrochemical study of high density spherical and non-spherical Ni(OH)2 as cathode materials for Ni–metal hydride batteries

In this paper we compare the behavior of non-spherical and spherical β-Ni(OH)2 as cathode materials for Ni–MH batteries in an attempt to explore the effect of microstructure and surface properties of β-Ni(OH)2 on their electrochemical performances. Non-spherical β-Ni(OH)2 powders with a high-density are synthesized using a simple polyacrylamide (PAM) assisted two-step drying method. X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), thermogravimetric/differential thermal analysis (TG–DTA), Brunauer–Emmett–Teller (BET) testing, laser particle size analysis, and tap-density testing are used to characterize the physical properties of the synthesized products. Electrochemical characterization, including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and a charge/discharge test, is also performed. The results show that the non-spherical β-Ni(OH)2 materials exhibit an irregular tabular shape and a dense solid structure, which contains many overlapped sheet nano crystalline grains, and have a high density of structural disorder and a large specific surface area. Compared with the spherical β-Ni(OH)2, the non-spherical β-Ni(OH)2 materials have an enhanced discharge capacity, higher discharge potential plateau and superior cycle stability. This performance improvement can be attributable to a higher proton diffusion coefficient (4.26 × 10−9 cm2 s−1), better reaction reversibility, and lower electrochemical impedance of the synthesized material.

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► This work focuses on the comparison between high-density non-spherical and spherical β-Ni(OH)2.
► Non-spherical materials exhibit a dense solid structure containing many overlapped sheet nano crystalline grains.
► Non-spherical Ni(OH)2 show markedly superior electrochemical performance comparing to spherical Ni(OH)2.