Study On The Controllable Preparation Of Ni₃S₂/NF Electrode Material And Its Electrochemical Performance

Lithium-ion batteries are considered to be the key to the large-scale deployment of electric vehicles and the use of renewable energy for stationary energy backup.Traditional lithium-ion batteries use graphite materials as the negative electrode,but there is a problem of low theoretical specific capacity,which limits its development.The room temperature resistivity of Ni₃S₂is only 1.2×10^-4Ω·cm,which is convenient for electron transmission,and the raw materials are abundant and easy to obtain,low-cost,and the preparation method is simple.The method for preparing nickel trisulfide is to obtain powder samples according to the mature preparation method of graphite at the beginning and prepare electrode materials through traditional mixing methods and coating.However,the traditional coating electrode materials have differences in coating processes.Such as nickel sheets,carbon cloth,carbon fiber paper,nickel foam,etc.Their common point is that they all have excellent conductivity,which can realize the rapid transmission of electrons,and can avoid the error caused by the coating process and the addition of non-conductive binder.At present,most of the preparation methods of Ni₃S₂are prepared by the one-step hydrothermal method.In this paper,a three-dimensional framework of nickel foam（NF）is used as the base material,and the Ni₃S₂in-situ growth is carried out on the conductive substrate nickel foam（NF）by two-step hydrothermal method.The purpose is to control the morphology of the precursor and further control the morphology of Ni₃S₂,to obtain Ni₃S₂monolithic composite electrode materials with controllable morphology.（1）The honeycomb Ni₃S₂/NF composite was prepared by a two-step solvent heat method.The purpose of the two-step hydrothermal method is that we can further control the morphology of Ni₃S₂by controlling the basic morphology of the precursor（Pre-NF）.The preparation process is based on foam nickel as the base material,deionized water as the solvent,nickel ion,cobalt ion,carbonate ion,and hydroxyl ion to solvothermal self-assembly.The precursor of bimetallic basic carbonate is obtained.Then,the target Ni₃S₂/NF composite is obtained by vulcanizing reaction of precursor under 160℃.SEM results show that the morphology of Ni₃S₂still keeps the honeycomb flocculent nanosheets of the precursor after vulcanization.The mutually supported vertical nanosheets can not only provide abundant electron transport paths but also provide space for slow-release volume expansion caused by the charge-discharge process.The physical,chemical,and electrochemical properties of the prepared materials and the batteries were characterized by scanning electron microscope（SEM）,X-ray diffraction（XRD）,and cyclic voltammetry.The initial discharge specific capacity of Ni₃S₂/NF electrode can reach 1494 m Ah g^-1at the current density of 100 m A g^-1,and the specific capacity of 1365 m Ah g^-1can be maintained after 1 A g^-1charge-discharge.After 100 cycles of 400 m A g^-1,the discharge capacity and specific capacity of Ni₃S₂/NF electrode decay from 1450 m Ah g^-1to 327 m Ah g^-1,and the decay rate of each cycle capacity is 0.7%.（2）Nano needle-like Ni₃S₂/NiO/NF composites were prepared by high-temperature calcination and hydrothermal method.The foamed nickel was pretreated with ethanol,hydrochloric acid,and deionized water,and then calcinated at 600℃and 2 h.Nano needle cluster morphology was synthesized by partial oxidation of NF and hydrothermal reaction.Through SEM analysis,firstly,the multilayer Ni₃S₂/NiO has dense encapsulation of NF,secondly,the pine needles have grown on NF by the in-situ method.These pine needles do not grow independently,but are interdependent and can be stacked as nanoneedle clusters,which can not only provide more abundant channels for electron transport but also increase the contact between active materials and electrolytes,which is conducive to ion diffusion.The contribution of the existence of nickel oxide to the material can be seen in the electrochemical performance test.With the participation of nickel oxide,the cycling performance of the anode material has been significantly improved.The physical,chemical,and electrochemical properties of the prepared materials and the batteries were characterized by scanning electron microscope（SEM）,X-ray diffraction（XRD）,and cyclic voltammetry.The initial discharge specific capacity of the multilayer composite is 1.982 m Ah cm^-2at 1m A cm^-2,and 0.829 m Ah cm^-2at 5 m A cm^-2.After 100 cycles at 2.5 m A cm^-2,the discharge specific capacity decays from 0.932 m Ah cm^-2to 0.462 m Ah cm^-2,and the decay rate of each cycle is 0.5%.（3）Ni₃S₂/NiO/NF nanosheet arrays were prepared by high-temperature calcination and hydrothermal method.The nickel foam was pretreated with ethanol,hydrochloric acid,and deionized water and then calcinated at 600℃and 2 h.The partial oxidation of NF by high-temperature calcination can account for about 5.8%of the total nickel foam.Then,with the partially oxidized NF as the substrate,Co（NO₃）₂·6H₂O and urea as reactants,the different curing time of the precursor is studied,and a multilayer composite structure with stacked nanoplates is determined as the electrode material.The physical,chemical,and electrochemical properties of the prepared materials and the batteries were characterized by scanning electron microscope（SEM）,X-ray diffraction（XRD）,and cyclic voltammetry.The results show that the initial discharge capacity is 1.55 m Ah cm^-2at 1 m A cm^-2and 0.761m Ah cm^-2at 5 m A cm^-2.After 100 cycles at 2.5 m A cm^-2,the discharge capacity decays from0.897 m Ah cm^-2to 0.471 m Ah cm^-2,and the decay rate of each cycle is 0.47%.