Design Of Hierarchical Porous Cathode Materials For Zn-Ion Batteries With Superior Performance

Nowadays,the main obstacle of current aqueous Zn-ion batteries is the lack of positive electrode materials with small electrochemical polarization,high specific energy and stable structure.To solve this problem,the main research content of this thesis is the preparation of high stability Zn-ion battery cathode materials.It mainly covers the following four parts:（1）The electrochemical performance comparison ofβ-Ni（OH）₂,NiO and Ni₃S₂electrode materials shows that Ni₃S₂ has smaller redox polarization and higher energy efficiency thanβ-Ni（OH）₂ and NiO electrode materials,we think that Ni₃S₂ is more suitable as a positive electrode material for water-based Zn-ion batteries.In order to improve the electrochemical performance of the Ni₃S₂ electrode material,we synthesize a 2D Ni-MOFs as the precursor,after one-step carbonization and sulfuration,Ni₃S₂@C nanosheet composite was prepared,Ni₃S₂ has a particle size of about 10 nm and uniformly dispersed on the porous carbon nanosheet substrate.By electrochemical performance testing,we found that Ni₃S₂@C has higher specific capacity,better rate performance and lower charging voltage thanβ-Ni（OH）₂,so it is more suitable for alkaline aqueous Zn-ion battery.（2）Since the high-valent oxidation state Co⁴⁺of Co has one more electron transfer than the high-valent oxidation state Ni³⁺of Ni,the Co-based compound has a higher theoretical specific capacity than the Ni-based compound.In order to further realize our pursuit of high energy dense zinc ion batteries,in this section we try to use a Co-based compound with a multi-electron transfer redox reaction as the positive electrode material for high energy density alkaline aqueous zinc ion batteries.Co₉S₈@C composite with 3D honeycomb structure was prepared by self-sacrifice template method by using Co-MOFs as the precursor.Compared the electrochemical performance with the Co₉S₈ electrode material prepared with traditional methods,we found that Co₉S₈@C composite material has higher specific capacity,better rate performance and higher cycle stability than Co₉S₈.Thereby,Co₉S₈@C composite is more suitable for alkaline water Zn-ion battery..（3）In this chapter,we have designed a simple and effective"sacrificial template guided self-assembly"method to construct MOFs superstructure materials with various specific three-dimensional structures by using MOFs nanocrystals as“Lego bricks”.We use self-assembled hollow urchin-like ZIF-67 superstructure as precursor,by Kendall effect and high temperature carbonization and sulfuration,successfully prepare hierarchically porous hollow urchin-like Co1-xS@C composites(HPHU-Co_1-x-x S@C).HPHU-Co_1-xS@C exhibits excellent electrochemical performance,specific capacity multiple of Co1-xS electrode material prepared by other methods,and is superior to Co1-xS electrode material prepared by other methods and other metal sulfides.（4）In this chapter,we report a new type Zn ion hybrid supercapacitor energy storage device with high energy density,high power density and long cycle performance.The device uses porous hollow carbon nanorods as the positive electrode,commercial Zn plate as the negative electrode,and ZnSO₄ as the electrolyte.The capacity of the hybrid Zn-ion supercapacitor exhibits the maximum specific capacity of 145 mA h g^-1at the current density of 1 A g^-1in the voltage range of 0.2 to 1.8 V.When the current density is increased to 50 A g^-1,its capacity can still be maintained about 46%.In addition,the hybrid supercapacitor also exhibits excellent cycle performance.At a current density of 10 A g^-1,after 10000 cycles test,the capacity retention is more than 95%,which is superior to most commercial batteries.We believe that this device is very suitable for the large-scale energy storage demand of safety,high rate and long cycle life,and is a very potential energy storage device.