Surface Modification And Sodium Storage Of Three Dimensional Ni₃S₂ Electrode

Ni₃S₂has excellent chemical stability and good electronic conductivity,high theoretical specific capacity as the negative electrode of sodium ion batteries.However,it still faces serious volume expansion and material powdering during cycling,resulting in poor cycle stability.In this thesis,structure design,surface modification and morphology controlling are employed to address these issues.（1）Three dimensional（3D）porous Ni is prepared by a electroless plating method,using the in-situ formed hydrogen bubbles dynamic as template and its morphology is controlled through adjusting the p H value and temperature of electroless plating solution.The results show that the pore structure of 3D porous Ni prepared under the conditions of p H=9 and 70℃is promising.Ni₃S₂nanosheet arrays are grown on the3D porous Ni by a hydrothermal method to achieve 3D porous Ni₃S₂electrode,and followed by phosphating treatment to obtain 3D porous phosphated Ni₃S₂nanosheet arrays.The porous structure can alleviate the volume change during the cycle,and the nanosheet array structure can shorten the electron transmission path.Besides,the surface phosphorized layer enhances the electronic conductivity and simultaneously stabilizes the electrode/electrolyte interphase to improve the electrochemical performance of the Ni₃S₂electrode.As the anode of sodium-ion battery,the 3D porous phosphorized Ni₃S₂electrode can provide a specific capacity of 387.5 m Ah g^-1after 100 cycles at 100 m A g^-1,a high reversible capacity of 362.4 m Ah g^-1even at a high current density of 1.6 A g^-1.（2）3D porous Ni₃S₂electrode with a mixed morphology of nanosheets and nanotubes is prepared by a hydrothermal method using 3D porous Ni as the substrate,followed by constant potential depositing In layer on it.Under the synergistic effects of the 3D porous structure and In coating layer,the 3D porous Ni₃S₂@In electrode shows a high first coulombic efficiency of 87.4%and a specific capacity of 457.8m Ah g^-1after 150 cycles at 100 m A g^-1,a high specific capacity of 325.4 m Ah g^-1even at high current density of 1.6 A g^-1.（3）The morphology of 3D porous Ni₃S₂electrode is adjusted through controlling hydrothermal treatment time,and the influence of different morphologies on its electrochemical performance was studied.The results show that 3D porous Ni₃S₂electrode tends to generate nanosheet arrays in a shorter hydrothermal treating time.As the hydrothermal treating time increases,they gradually transform to nanotube arrays,and finally completely transform into nanotube structures.The 3D porous Ni₃S₂nanotube arrays electrode have the best long cycle and rate performance,the specific capacity remains at 279.1 m Ah g^-1,and the retention is 53.7%after 200cycles at 100 m A g^-1,higher than 3D porous Ni₃S₂nanosheet arrays electrode（26.6%）and 3D porous Ni₃S₂electrode with nanosheet and nanotube mixed morphology（38.7%）,high capacity of 291.1 m Ah g^-1even at the current density of 1.6 A g^-1.