Synthesis And Electrochemical Properties Of Nickle Sulfides And Selenides With Novel Micro-Nano Structures

Currently, it is of great interest to find more reliable anode materials for lithium ion battery due to the commercial anode materials, graphite-based materials, has been could not meet the demand of the high-energy lithium-ion batteries applications.Among all the new generation of anode materials, the transition metal chalcogenides, especially nickel-based chalcogenides have been receiving more and more attention due to their high theoretical specific capacity, low-cost and esay to synthesize. In addition, lots of studies have found that the electrode materials with special structures in nano scale will be greatly enhanced the performance of lithium ion batteries.In this paper, a series of nickel sulfides and nickel selenides with special morphologies and structures have been synthesized in situ on the nickel foam with3D frame work successfully via a facile solvothermal method and the growth mechanism and the electrochemical performance of as prepared products have also been researched. The follows is the detail of this paper:Firstly, large-scale stereoscopic structured heazlewoodite (Ni3S2) microrod arrays and scale-like microsheets were successfully prepared by a facile and environmentally benign approach, in which deionized water and ethanol were used as the environmentally friendly solvent.Uniform bamboo shoot-like Ni3S2microrods and scale-like Ni3S2microsheets were distributed evenly at the surface of a porous three-dimensional nickel substrate. Studies found that the growth process of Ni3S2is dependent on the reaction temperature and solution polarity. An increase in reaction temperature could achieve a rod structure while an increase in solution polarity could obtain a denser structure. Due to the large surface area and regular morphology, the stereoscopic structured Ni3S2microrod arrays and scale-like Ni3S2microsheets were employed as cathode materials for lithium-ion batteries, and the initial discharge capacity of Ni3S2microrod arrays reached592mAh g-1.Secondly, a series of nickel sulfide nanocrystallines with hierarchical structures was successfully fabricated in situ on a nickel substrate. The nanocrystalline materials with three dimensional (3D) structures were synthesized via self-assembly under moderate conditions, with ethylenediamine and ethylene glycol as the mixed solvents. The structure and morphology of each nickel sulfide could be controlled by adjusting the polarity of the mixed solvents.With the reduced solvent polarity, the 3D flower like nickel sulfide spheres were transformed into two-dimensional (2D) nanoflakes, then into one-dimensional (1D) prism-like microrods, and finally into1D pearl-like nanochains. When the nickel sulfides were used as electrode materials in lithium-ion batteries, the obtained samples with different morphologies had different initial discharge capacities. The initial discharge capacity of the as-prepared nickel sulfides with1D nanostructures reached approximately550mA h/g, which was higher than that of the samples with2D and3D structures.Thirdly, tubular nickel selenide (NiSe) crystals with hierarchical structures were successfully fabricated using a one-step solvothermal method in moderate conditions, in which ethylenediamine and ethyleneglycol were used as the mixed solvent. The growth of hierarchical NiSe microtubes from NiSe microflakes was achieved without surfactants or other chemical additives by changing the reaction time. When the as-synthesized NiSe microtubes were employed as cathode materials for lithium-ion batteries, the initial discharge capacity of hierarchical NiSe microtubes reached410.7mAh g-1.At last, a facile one-pot method was reported for the synthesis of a series of nickel selenide nanocrystalline grown in situ on nickel foam with a3D framework via the use of mixed solution. Through adjustment of the composition of mixture solution, reaction temperature and reaction time, NiSe nano-dandelion arrays, Ni3Se2with3D pine branch-shape structure and nano-sized grass-like Nio.9sSe arrays were obtained. The process of the synthesis of nickel selenide nano-dandelion arrays has been proposed in this paper. This method provided a suitable nucleation and growth environment in a uniform and transparent solution reaction system. Moreover, the electrochemical properties of all the as-prepared nickel selenide have been studied.