Preparation of spherical NiCo₂S₄ and the electrochemical behavior in KOH solution

In NiCo₂S₄, Ni and Co will participate in the charging-discharging process at the same time to obtain higher specific discharge capacity and energy density. Moreover, it is helpful to promote the further development of electrode materials by analyzing the contribution rates of double layer capacitance and pseudocapacitance in NiCo₂S₄. The spherical electrode material of nickel cobaltate (NiCo₂S₄) with excellent electrochemical performance was prepared through hydrothermal synthesis method using cobaltous acetate as Co source, nickel acetate as Ni source and thioacetamide as precipitant. The phase, morphology, composition and pore structure of NiCo₂S₄ were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, mapping and N₂ adsorption-desorption techniques. Besides, the electrochemical behavior in KOH electrolyte was investigated. The results display that the spherical NiCo₂S₄ is successfully prepared and the ratio of Ni, Co and S is 1∶2.1∶4.2. NiCo₂S₄ is a cubic phase polycrystal and the lattice constant is 0.9387 nm. In the lattice of NiCo₂S₄, Ni and Co exist in the form of Ni²⁺/Ni³⁺and Co²⁺/Co³⁺. The pore volume of NiCo₂S₄ is 0.402 cm³/g and the proportion of mesoporous pores is 90.6%. In KOH solution, both of double layer capacitance and pseudocapacitance are generated and the ratios are 60.6% and 39.4%. When the current density is 0.2 A/g, the specific discharge capacity is 409.7 F/g, energy density is 14.2 W·h/kg. After 10000 cycles, the capacity retention is 90.3%.