Design Of Functional Layer On The Surface Of Porous Carbon For Zinc Anode And Its Reversibility Study

With the continuous development of the economy and society,energy and environmental issues have become increasingly prominent.In particular,the surge in energy demand has put enormous pressure on energy supply.Therefore,it is urgent to find new energy technologies to solve these problems.As a new type of battery,rechargeable zinc-air batteries have received widespread attention in recent years due to their high energy density,low cost,and environmental friendliness,and are considered to be an important direction for future energy storage and power battery development.In particular,compared with traditional lithium-ion batteries,zinc-air batteries have two main advantages.On the one hand,the energy density of zinc-air batteries is much higher than that of lithium-ion batteries,which means that they can store more energy and have a longer range.On the other hand,the cost of zinc-air batteries is much lower than that of lithium-ion batteries,which gives them a great advantage in large-scale commercial applications.However,rechargeable zinc-air batteries still face some challenges and problems,such as zinc dendrite formation,corrosion,passivation,and deformation,all of which directly affect the reliability and cycle life of the battery.Therefore,how to suppress various parasitic reactions of the zinc anode is the key to improving the performance and cycle life of zinc-air batteries.In this thesis,polyquaternium-7（PQ-7）was used as the carbon and nitrogen source,and a series of nitrogen-doped mesoporous carbon（N-MC）anode functional layer materials were successfully prepared by the hard template method（nano-sized silica as the template agent）,through a process of first carbonization,alkali etching pore formation,and second carbonization.The basic physicochemical properties of the mesoporous carbon anode functional layer were characterized by XRD,SEM,TEM,BET,and other spectroscopic characterization methods,and the electrochemical performance and battery performance of the mesoporous carbon anode functional layer were obtained by assembling symmetrical cells and zinc-air batteries.Combining the spectroscopic characterization results and electrochemical performance evaluation parameters,the correlation and mechanism between the intrinsic structure and electrochemical performance of the mesoporous carbon anode functional layer were summarized.The main content and results of this thesis are as follows:（1）A highly efficient and reversible metal-free nitrogen-doped mesoporous carbon（N-MC）anode functional layer material was successfully obtained by the hard template method.The study showed that the prepared nitrogen-doped mesoporous carbon（N-MC）had an unordered sponge-like multi-level pore structure and a high specific surface area(620 m³ g^-1).The multi-level pore structure and high specific surface area provided sufficient buffer zones for the deposition and dissolution of zinc ions,which is beneficial to improve the reversibility of the zinc anode.The N-MC@Zn composite zinc negative electrode can be prepared by coating the slurry on a zinc foil.The results of symmetrical cell testing showed that the N-MC@Zn composite negative electrode can not only reduce the overpotential of the battery（0.878V）,but also effectively improve its hydrophobicity（increasing the hydrophobic effect and suppressing hydrogen evolution corrosion）.（2）A highly efficient and reversible single-atom zinc-nitrogen co-doped mesoporous carbon（Zn/N-MC）anode functional layer material was successfully obtained using Zn SO₄·7H₂O as a metal inducing agent based on the hard template method.Inspired by the use of electrospun Zif-8 composite materials as zinc ion battery SEI layers to improve battery cycling life,this study further optimized the N-MC@Zn composite electrode by adding Zn SO4·7H2O during precursor preparation.The physical characterization and electrochemical test results showed that the zinc-nitrogen co-doped mesoporous carbon（Zn/N-MC）has a larger specific surface area(1020m³ g^-1)and more abundant mesoporous structure（formed by zinc volatilization induction）than N-MC.XPS testing showed the presence of three elements,Zn,N,and C,and the formation of a unique high electronegativity Zn-Nx/C structure.Zn/N-MC@Zn composite zinc negative electrode assembled into a symmetrical cell showed lower overpotential and longer cycle life than N-MC@Zn under high rate(10m A cm^-2)and low rate(1m A cm^-2)discharge conditions（650h and400h,respectively）.Similarly,the cycle life of the zinc-air cell assembled with Zn/N-MC@Zn composite zinc negative electrode was improved from 220h for Bare Zn negative electrode to480h.（3）The mechanism of the effect of the calcination temperature and zinc salt addition amount on the Zn/N-MC anode functional layer material was preliminarily understood.The study showed that the calcination temperature can not only control the Zn content loaded in the carbon material and regulate the mesoporous formation rate,but also control the graphitization degree of the anode functional layer material and improve its conductivity.The test results showed that the Zn/N-MC functional layer treated at 950^oC showed the lowest charge-discharge overpotential.The above structure validation demonstrates that high-temperature calcination can promote the graphitization degree of the carbon material,improve its conductivity,and reduce the reaction overpotential.In addition,when the zinc salt addition amount was 1.5g,the symmetrical cell prepared by Zn/N-MC@Zn showed better cycle stability at high current density(10m A cm^-2)than the other two composite electrodes.These results indicate that there is an optimal range for the addition amount of the metal inducing agent;generally,increasing the amount of zinc salt is beneficial to the enrichment of the pore structure and the formation of a larger specific surface area,but too much addition can lead to the existence of abundant atomic-level zinc metal in the functional layer,which can cause more serious hydrogen evolution reaction and reduce the life of the zinc anode.