Structure Control Of Zinc Storage Materials And Their Electrochemical Performance

Metal zinc possesses safety,high global production,low cost and redox potential,which make zinc has been widely used in the various rechargeable energy storage systems,including Zn-ion batteries（ZIBs）and Zn-ion hybrid capacitors（ZICs）.The development and design of Zn ions storage materials are the vital concern of Zn-ion energy storage equipment.However,Zn ions storage materials still suffer from significant challenges,such as low Zn ions storage capacity,slow Zn ions diffusion and poor conductivity.It has been demonstrated that optimizing microscopic and electronic structure of electrode materials is an efficient strategy to enhance Zn ions storage capacity.This paper regulates the microscopic and electronic structure of materials through introducing defects and doping heteroatoms to further improve the Zn ions storage capacity,Zn ions diffusion rate and conductivity of materials.Besides,the relevant mechanisms have also been explored.The main research contents and results of this paper were summarized as follows:（1）The 3D microflower-like ZnCo₂O₄material was synthesized by a simple solvothermal method and abundant oxygen vacancies were introduced(ZnCo₂O_4-x).This 3D microflower structure could reduce inherent ion and charge transport resistance,improve reaction kinetics and accelerate the transport of Zn ions.Oxygen vacancies not only improve the concentration of storage sites and enlarge diffusion channels,but also enhance the electronic conductivity.The ZnCo₂O_4-x//Zn batteries achieve an admirable capacity of 148.3 m Ah g^-1at the current density of 0.05 A g^-1,32%capacity retention when current density up to 0.5 Ag^-1and good long-term stability with capacity retention of more than 84%after 1000 cycles.（2）We synthesized the polymer precursor（PTHB）by polycondensation,and PTHB was carbonized at high temperature with B atom doping to obtain the ultrathin porous carbon nanobelts with B,N,O doping（CPTHB-Bx）,which as new cathodes for aqueous ZICs.The ultrathin nanobelt microstructure could shorten the distance of charge transfer in multiple dimensions.The heteroatom doping can obviously modify chemistry characteristics of carbon framework,which could generate numerous active sites and accelerate Zn ions transport.Meanwhile,the doping amount of B atom was controlled and the influence mechanism of B atom on the Zn ions storage capacity was identified.As a result,the best-performed CPTHB-B2//Zn exhibits a good electrochemical performance,delivering a delightful specific capacitance of 415.3 F g^-1at 0.5 A g^-1,81%capacitance retention at current densities from 0.5 to 100 A g^-1,a nearly 100%capacitance retention after 10000 cycles(10 A g^-1),an outstanding energy density of 131.9 Wh kg^-1and an exceptionally high power density of 42.1 k W kg^-1.（3）Flexible Zn-ion energy storage devices were assembled with as-designed two materials,PAM/Zn SO₄gel electrolyte and Zn-deposited carbon cloth.Flexible ZnCo₂O_4-x//Zn battery presents a specific capacity of 64.5 m Ah g^-1at 0.5 A g^-1based on the mass of active materials and the Coulombic efficiency is approximately 100%.Flexible CPTHB-B2//Zn hybrid capacitor affords an excellent mass specific capacitance of 245.7 F g^-1and an area specific capacitance of 840.7 m F cm^-2at 5 A g^-1.Two Zn-ion energy storage devices deliver extremely stability under different bending states,revealing the application prospects in flexible electronic devices.