In this paper, we research the influence of Ni element doping on the structure and electrochemical properties of LiCoO₂. The results show that Ni element doping can reduce initial coulomb efficiency and discharge capacity of materials, and the higher the doping amount, the lower the quantity. A small amount of Ni element doping can improve layer structure of the material, and some Ni elements enter Li plane, support Li plane, and better stabilize layer structure of the material. At the same time, a small amount of Ni element doping can reduce charge transfer impedance of the material during charging-discharging process, so that the material has better cyclic performance. However, when Ni doping is too much, structural stability of the material is reduced, charge transfer impedance is increased, and cyclic performance is deteriorated.

Spherical CoCO₃ powder with a small particle size and high density was successfully prepared using a continuous carbonate liquid precipitation method with a raw material of cobalt chloride solution, a precipitant of NH₄HCO₃, and without a template. The effects of the concentration of ammonium carbonate, process pH, and feeding rate on the tap density and apparent density of cobalt carbonate were investigated. It was found that the apparent and tap density values of 4.4 µm of cobalt carbonate were 1.27 g/cm³ and 1.86 g/cm³, respectively, when the initial concentration of NH₄HCO₃ solution was 60 g/L, the pH was 7.15–7.20, and the feeding rate of cobalt chloride was 2 L/h. The anisotropic growth process of the crystal lattice plane of CoCO₃ under the aforementioned optimal conditions were studied. The results demonstrated that the crystal grew fastest along the (110) facet orientation, which was the dominant growth surface, determining the final morphology of the primary particles. The scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) results demonstrated that the primary particle morphology of the cobalt carbonate was a nanosheet. The unit cell of cobalt carbonate, of a hexagonal structure in the horizontal direction, grew horizontally along the (110) facet orientation, while 20–35 unit cells of the carbon carbonate were stacked along the c-axis in the thickness direction. Finally, the sheet-shaped particles were agglomerated into dense spherical secondary particles, as presented through the crystal re-crystallization model.

In this study, green and efficient method for recycling valuable metals from scrapped lithium cobalt oxide cathode materials to form lithium carbonate and cobalt powder was proposed. To this end, aluminum and iron impurities were efficiently removed from scrapped lithium cobalt oxide cathode materials through alkali dissolution and magnetic separation with removal rates of 99.9% and 98.3%, respectively. After removal of impurities, lithium cobalt oxides were reduced by hydrogen at high temperature of 650 °C for 3 h to yield Li2O, Co, and very small amounts of CoO and LiOH. Next, the mixture was subjected to water leaching and sodium carbonate precipitation to obtain lithium carbonate with purity of 99.5%. The water-leaching Co and small amounts of cobalt oxides were again reduced by hydrogen to form cobalt powder with purity of 99.4%. In sum, the proposed method looks promising in terms of efficiency, easy for implementation, environmentally-friendliness, and potential industrialization.

This research examines the influence of NH₄⁺ impurities and seed ratio on growth mechanisms and characteristics of nickel sulfate hexahydrate in batch cooling crystallization. The kinetic behavior, thermal properties, and functional groups were also studied under the influence of NH₄⁺ impurities. At low concentrations of impurities, competing process between Ni²⁺ and NH₄⁺ ions to bind with SO₄²⁻ causes the crystal output yield and growth rate to decrease and the crystallization activation energy increases. At high concentrations of impurities, NH₄⁺ ions incorporate into crystal structure and produce double salt (NH₄)₂Ni(SO₄)₂ 6H₂O. The formation of double salt causes the crystal output yield and growth rate to increase and the crystallization activation energy decreases. The presence of NH₄⁺ ions, whether in low or high concentrations, induces structural distortion in the crystal lattice and the crystals could exhibit heat stability up to 80 °C. Furthermore, crystal growth mechanisms can change significantly affected by NH₄⁺ impurities rather than seed ratio. Impurity tends to attach to the crystal when the impurity concentration is low and impurity can be incorporated when the concentration is high. The seed ratio significantly increases crystal output yield and slightly increases crystal purity.