Preparation And Electrochemical Properties Of NiS Nanomaterials With Hollow Structure

Nickel sulfide has become one of the most promising materials for high performance energy storage devices because of its high theoretical specific capacity,rich phase composition and low cost.The researchs about nickel sulfide as electrode materials for supercapacitors or lithium-ion batteries have also been more and more attention.However,the traditional nickel sulfide as the electrode material has poor conductivity and bad cycling stability,which limit its practical application.In this paper,by designing the hollow structure with high specific surface area and good surface permeability,we prepared successfully the double-shell hollow NiS nanomaterials with controlled shapes and NiS carbon-based composite hollow microspheres,and then investigated their electrochemical properties.Firstly,double-shelled NiS hollow materials with capsule-,ellipsoid-and cubic-shaped were successfully prepared by using α-Fe₂O₃ with different morphologies as hard templates.The as-obtained NiS materials have uniform size and well-designed double-shelled hollow nanostructure,and its shell is formed by the accumulation of ultra-thin NiS nanosheets.Due to its high specific surface areas（100.2 m2/g）and optimal pore distribution,low equivalent series resistance（0.80 Ω）and ion diffusive resistance,electrodes prepared by the capsule-shaped NiS exhibit the highest specificcapacitance of 1159 F/g at a current density of 2 A/g.Moreover,the asymmetric supercapacitors NiS（capsule-shaped）||RGO@Fe₃O₄ exhibits high energy density（43.7 Wh/kg at 664 W/kg）and cycle stability（83.3% retention after 5000 cycles）.Secondly,C@NiS hollow structure was designed and synthesized.In the process of preparation,we utilized the aerosol method to prepare C@SiO₂ hollow microspheres,which simplify the experimental steps of hollow SiO₂ prepared by hard-template method.Meanwhile,the introduction of carbon material would be beneficial to the charge transfer.The outer shell of as-obtained C@NiS material is formed by the accumulation of NiS nanosheets,and the inner shell is carbon layer.When the C@NiS hollow material was used as the anode material of the lithium ion battery.The internal resistance Rs is reduced from 21.1 Ω of pure NiS hollow material to 8.0 Ω.After 100 cycles at the current density of 200 mA/g,the specific capacity of C@NiS electrode is 131.6 mAh/g,which is about 2.5 times of that of pure NiS.Finally,to improve the dissolution of the electrode active material caused by the volume change of NiS in the process of intercalation/deintercalation behavior of Li+,C@NiS@RGO hollow nanocomposites was successfully prepared by coating the C@NiS material with reduced graphene oxides.The encapsulation of graphene effectively alleviates the volume change of NiS and reduces the interface charge transfer resistance（Rct）of the material,which greatly improves the electrochemical performance of the material.When the current density is increased from 200 mA/g to 2000 mA/g,the specific capacity of the C@NiS@RGO material is reduced from 478 mAh/g to 93 mAh/g,while the C@NiS capacity under the same conditions is from 165 mAh/g to 7 mAh/g.