Simulation Of Crystal Growth Of NiCl₂ And CoS₂

Nickel choloride（NiCl₂） and cobalt disulfide（CoS₂） have been widely researched and applied in the field of thermal battery as the cathode materials. The crystal growth of NiCl₂ and CoS₂ was studied by the density functional theory（DFT）. The surface energy and electronic structures of the major faces of NiCl₂ and CoS₂ were calculated to determine the thermodynamic stabilities and the growth rate in the vacuum environment. The adsorption of water molecule and ethanol molecule on the surfaces of NiCl₂ and CoS₂ was researched by DFT. BFDH method was used to predict the possible crystal morphology of NiCl₂ and CoS₂. The main research contents of this paper are as follows:（1） The periodic slab models, the surface energy and electronic structures of NiCl₂ were determined by the CASTEP program in Materials Studio software. The results indicate that the surface energy of（003） is the smallest, indicating that the surface is the most stable thermodynamically. The front valence electron of（003） is active. It indicates that there may be some activity points on this face. The adsorption of water molecule and ethanol molecule on the NiCl₂ surfaces were researched by DFT. The results of the adsorption energy show that, the adsorption capacity of ethanol molecule on each face are significantly stronger than that of water molecule with the exception of（003） face. In aqueous solution, the growth rate of（003） face is significantly inhibited. In ethanol solution, the adsorption capacity of ethanol molecule on（003） is almost zero. Therefore, the crystal grows along the z-axis direction, leading to the rod morphology. This is consistent with the experimental results.（2） The periodic slab models, the surface energy and electronic structures of CoS₂ were determined by the CASTEP program. The results show that the stoichiometric surface（220）-2S and（211）-3S are more stable under S-rich condition. While（210）-Co and（111）-S become more stable with decreasing sulfur-lean. The electric structure results show that the front valence electron of（200） is active, which indicates that there may be some active points on this face.（220） and（211） faces are stable thermodynamically. The adsorption of water molecule on the Co S₂ surfaces was studied by DFT. The results show that the adsorption capacity of water molecule on the（200） surface is the strongest.（3） BFDH method was used to predict the morphology and crystal growth habit of NiCl₂ and CoS₂. The results show that the morphology of NiCl₂ may be lump or rod, which is consistent with the experimental results. CoS₂ crystal may be obtained in the spheroidal, octahedral, cube-shaped, prismatic or plate-like shape. The first two kinds were obtained in the experiments.