Defect Construction And Electrochemical Properties Of Nickel Cobalt Hydroxide

With the goal of"carbon neutrality"being put forward,it is imperative to optimize the energy structure and develop efficient energy storage technologies.Supercapacitors have high power density and low power loss,making them suitable for using as energy storage devices for stabilizing power grids.The key challenge for supercapacitors is to increase capacity and maintain lifetime.Among various materials,layered double hydroxides（LDHs）have shown good application prospects in the field of energy storage due to their layered structure and tunable elemental composition.However,the low electrical conductivity and poor structural stability of LDHs seriously affect their applications.The template method can regulate the morphologies and structures of LDHs in a simple way.By introducing defects,its electrical conductivity and energy storage performance can be improved.In this paper,to improve the energy storage performance of LDHs,the materials are designed and synthesized from the perspective of structure adjustment and defect introduction,and the electrochemical energy storage performance of them is studied.The main research contents are as follows:（1）Using Co-ZIF as a sacrificial template,nano flakes were self-assembled into hydrangea-like spheres that further constructed hollow cage structure.By tuning the Ni/Co ratio,introduce low angle grain boundary（LAGB）in the flakes of NiCo-LDHs,which further promoted the formation of oxygen vacancies.The synthesized electrode exhibits excellent specific capacity and rate performance,899 C g^-1 at 1 A g^-1;and the capacitance retention is 72%at 10 A g^-1.The assembled NiCo-LDH-2//AC hybrid supercapacitor has a high specific capacitance of 373 F g^-1 at a current density of 1 A g^-1;when the current density is increased to 20 A g^-1,its capacitance maintains 70%.The capacitor achieves an energy density of 101.1 Wh kg^-1 at a power density of 1500W kg^-1,and the capacitance retention was 87%after 5000 cycles at a current density of2 A g^-1,indicating that the hybrid supercapacitor has excellent rate capability and good cycling stability.（2）NC-LDH/S@CC nanosheet arrays were successfully synthesized through ion exchange and low-temperature hydrothermal sulfur doping,eliminating the conductivity caused by the binder.After S doping,the nanosheet spacing was reduced,and NC-LDH/S formed an amorphous structure,which can prevent the decrease in stability caused by volume expansion;at the same time,NiCo₂S₄ nanoparticles are embedded at the tip of nanosheets,which can further improve the conductivity of the material.The flexible electrode has a wide voltage window（0.6 V）and a high specific capacity,with a specific capacity of 1007 C cm^-2 at 1 m A cm^-2,and a specific capacity retention of 67%at 10 times the current density.The assembled NC-LDH/S//AC flexible hybrid supercapacitor can achieve a high specific capacitance of 1867.2 m F cm^-2 at 5 m A;a maximum energy density of 0.664 m Wh cm^-2 is achieved at a power density of 0.556 m W cm^-2.After 2000 cycles at a high current of 20 m A,the capacitance retention rate was 82%;even when folded completely,the flexible device still maintained a CV area of 66%.It is shown that the flexible hybrid supercapacitor has excellent rate capability and good cycling stability with considerable flexibility.