Construction And Electrochemical Energy Storage Of Three-dimensional Ni₃S₂ And NiOOH Electrodes

Transition metal sulfide Ni₃S₂ has the advantages of easy preparation,low cost,safety and non-toxicity and high specific capacity,is widely used in the field of electrochemical energy storage batteries.However,it has great volume changes during charging/discharging,and the active material is easy to be pulverized and peeled off,result in poor cycle life and high rate capacity.As we know,the morphology has great effect on the electrochemical performance.In this thesis,a three-dimensional Ni₃S₂ electrode was constructed,and TiN layer was coated on its surface.The performance of the Ni₃S₂electrode as a negative electrode for zinc/sodium ion batteries was studied.Besides,NiOOH prepared by hydrothermal treatment and anodizing is studied as cathode of Zn-ion battery.The main research contents are:（1）Three-dimensional porous nickel was grown on the nickel foam by electroless plat method,the influence of pH on the pore structure of three-dimensional porous nickel was also investigated.A three-dimensional Ni₃S₂ electrode was grown on three-dimensional porous nickel by hydrothermal treatment.The results show that the first charge/discharge specific capacities of the three-dimensional Ni₃S₂ electrode at current density of 200 mA g^-1 are 216.8 and 137.4 mAh g^-1,with the first Coulombic efficiency is 63%.During the inital 40 cycles,the specific capacity continuously increase and reaches the maximum discharge specific capacity of 191 mAh g^-1,and then slowly decreases to 180.6 mAh g^-1in 170 cycles,with a capacity retention of 94%,which is significantly better than that of the Ni₃S₂electrode grown on the nickel foil substrate.The good electrochemical performance of three-dimensional Ni₃S₂ electrode attributables to its unique three-dimensional structure.The three-dimensional porous structure not only relieves the stress generated by the expansion/contraction of the electrode volume,but also provides a fast transmission channel for zinc ions.（2）TiN layer was coated on the surface of the three-dimensional Ni₃S₂ electrode by magnetron sputtering,named as TiN@3D Ni₃S₂ electrode.Compared with the three-dimensional Ni₃S₂ electrode,the initial discharge and charge specific capacity of TiN@3D Ni₃S₂ electrode are smaller a little,which are 144.1 mAh g^-1 and 93.2 mAh g^-1,respectively,but the cycle performance is better.The discharge specific capacity still maintaining 145.1 mAh g^-1 after 240 cycles.The TiN layer can increase the electrode electronic conductivity and enhance the electrode/electrolyte interface stability,thereby improving the cycle stability of the three-dimensional Ni₃S₂ electrode.However,the TiN layer itself is inactive,which reduces the specific capacity of the electrode.（3）In layer is coated on three-dimensional Ni₃S₂ electrode by electrodeposition,named as In@3D Ni₃S₂ electrode.The results show that the initial discharge and charge specific capacities of the In（20s）@3D Ni₃S₂ electrode are 137.4 mAh g^-1/317.6 mAh g^-1with an inital coulombic efficiency is43.2%.After 150 cycles,the specific capacity remains 41.2 mAh g^-1.（4）Ni（OH）₂ nanosheets are hydrothermally grown on three-dimensional porous nickel,and then anodized under different potential conditions to obtain NiOOH electrode.The initial charge and discharge specific capacities of NiOOH（0.7 V 20 min）electrodes are 315 mAh g^-1 and 122.4 mAh g^-1respectively,with an initial Coulombic efficiency of 38.8%.The reversible specific capacity after 250cycles still remains 38.8 mAh g^-1.（5）The TiN@3D Ni₃S₂ electrode is used as the negative electrode of sodium ion battery.The results show that the reversible capacity remains 449.3 mA g^-1 after 130 cycles at a current density of100 mA g^-1,which slightly better than the three-dimensional Ni₃S₂ electrode.The electrochemical performance improvement of the Ni₃S₂ electrode can be attributed to its unique micro-nano structure.The three-dimensional porous structure effectively alleviates the large volume change of the Ni₃S₂electrode during the electrochemical cycle,and slows down the active material puverization rate.Meanwhile,the TiN conductive film provides high electronic conductivity and protects the electrode/electrolyte interface.（6）Metallic In layer coated three-dimensional Ni₃S₂ electrode（In@3D Ni₃S₂ electrode）show the initial discharge and charge specific capacities of 1451.9 mAh g^-1 and 1135.8 mAh g^-11 respectively at a current density of 100 mA g^-1,with a first coulomb of 76%.After 130 cycles,the specific capacity maitains 322.4 mAh g^-1.The cycle stability is better than that of the 3D Ni₃S₂ electrode,but is slightly worse than that of theTiN@3D Ni₃S₂ electrode.