The electrochemical behavior of Ni(OH)2 in KOH solution containing aluminum hydroxide

In this paper Co-doped Al-substituted α-Ni(OH)2 was prepared by a homogeneous precipitation method and its electrochemical behavior, in two kinds of electrolyte (7 M KOH solution and 7 M KOH saturated with Al(OH)3), was investigated by galvanostatic charge-discharge method, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrochemical properties of the commercial β-Ni(OH)2 in both electrolyte was also studied in order to compare with that of α-Ni(OH)2. The results show that Co-doped Al-substituted α-Ni(OH)2 has the largest capacity in 7 M KOH solution (300 mAh g−1). The addition of Al to KOH solution is harmful to the reversible capacity and cycle life of both α-Ni(OH)2 and β-Ni(OH)2. X-ray diffraction (XRD) patterns show that, for Co-doped Al-substituted α-Ni(OH)2, its turbostratic structure maintains after cycles in both alkaline electrolyte, despite the interlayer distance becoming smaller. For β-Ni(OH)2, however, γ-NiOOH species appeared after cycling in both electrolyte and its content is higher after cycling in 7 M KOH saturated with Al(OH)3. And adding Al into KOH solution caused the decrease of solution conductivity and increased the apparent diffusion coefficient which is evidenced by electrochemical impedance spectroscopy.