Synthesis and electrochemical performance of mixed phase α/β nickel hydroxide

Nickel hydroxide with a unique α/β mixed phase structure is synthesized by partially substituting Al3+ for Ni2+ with chemical coprecipitation method. The physical properties of the synthesized Al-substituted α/β-nickel hydroxide are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry analysis (TG), scanning electron microscopy (SEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and tap density testing. The results show that the Al-substituted α/β-nickel hydroxide exhibits an irregular shape and contains many intercalated water molecules. In particular, the tap density of the Al-substituted α/β-nickel hydroxide reaches 2.02 g cm−3, which is significantly higher than that of α-nickel hydroxide. The electrochemical performances of the prepared samples are characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge tests. The results demonstrate that the Al-substituted α/β-nickel hydroxide has much higher electrochemical activity, better electrochemical reversibility, lower electrochemical reaction impedance, and higher discharge voltage than the pure β-nickel hydroxide. The specific discharge capacity of the Al-substituted α/β-nickel hydroxide maintains to be 325.4 mAh g−1 (or 657.3 mA h cm−3) after 100 cycles at a charging/discharging current density of 200 mA g−1 under ambient temperature.

► Al-substituted nickel hydroxide with a unique α/β mixed phase was synthesized by a chemical coprecipitation method.
► The Al-substituted α/β-nickel hydroxide has a high tap density of 2.02 g cm−3.
► The α/β-nickel hydroxide combines both the advantages of α-nickel hydroxide and β-nickel hydroxide.
► The α/β-nickel hydroxide has a higher discharge capacity and better cyclic performance than the pure β nickel hydroxide.