Design And Performance Study Of Multi-stage Structure Of Zinc-based Anode With High Specific Energy Based On Seawater System

The method of obtaining energy from the burning of fossil energy is still the mainstream at present,and some problems that follow,such as energy crisis and environmental crisis,are still the mainstream.There is an urgent need for the emergence of alternative energy sources.At present,clean and renewable energy is the key to solving the above problems.It is usually converted into efficient and convenient electrical energy for use,such as solar power,wind power,and hydropower.However,for the intermittent nature of renewable energy and the characteristics of environmental influence factors,the direct use of the converted electric energy cannot meet the practical requirements,so how to store this energy safely and efficiently is the key strategy to deal with the crisis at the moment,that is,large-scale storage.The development of energy technology.Electrochemical energy storage has many benefits and has always been the focus of research.To truly achieve the purpose of large-scale energy storage,it needs to meet:low cost,safety and stability,good performance,high efficiency,and a system without natural environmental restrictions and pollution.The water-based zinc-ion battery has entered people’s field of vision because of its low cost,safety,and mature research,but there are also some problems,such as dendrites,and the method of solving dendrites is the design of electrode structure.In this dissertation,zinc-air battery based on seawater system to meet the requirements of large-scale energy storage is developed.The 3D porous thin film zinc electrode（3D-Zn@NF）is constructed on the foamed nickel substrate by electrodeposition method to achieve the purpose of high specific energy and reduce the generation of zinc dendrites.Considering the background of large-scale energy storage,cost reduction is the key.The use of chemicals as a solvent will increase the cost,seawater as a natural electrolyte is inexhaustible and inexhaustible.It is imperative to develop an electrolyte based on seawater.Similarly,the reactant of the air electrode is oxygen in the air.Resources are endless.The main research contents of this dissertation are as follows:（1）Zinc flakes,3D porous thin film zinc electrode（3D-Zn@NF）in alkaline electrolyte,and 3D porous thin film zinc electrode（3D-Zn@NF）in Zn SO₄ electrolyte based on deionized water system were studied respectively and based on the electrochemical behavior in the seawater system Zn SO₄ electrolyte（Zn SO₄-SW）,through constant current charge and discharge curve,cycle performance based on the analysis of coulomb efficiency,3D-Zn@NF electrode is more reversible than zinc flakes.The3D-Zn@NF electrode performs better in Zn SO₄ electrolyte based on seawater system（Zn SO₄-SW）than in alkaline electrolyte and Zn SO₄ electrolyte based on deionized water system.（2）The 3D-Zn@NF electrode was characterized,and the charge-discharge mechanism of the electrode(oxidation-reduction reaction between Zn and Zn²⁺)was confirmed by XRD and CV.Through the SEM characterization of the electrode during the charging process,it was found that the multi-level structure was clustered,flake-shaped,and granular.Through a series of electrochemical characterizations,the study found that when the current density is increased from 100 m A cm^-2 to 500 m A cm^-2 at equal intervals,the charge specific capacity is maintained at 200 m Ah cm^-2,and the discharge specific capacity is in the range of 195.6 m Ah cm^-2～198.7 m Ah cm^-2,stable charging and discharging voltage platform,showing excellent rate performance.Similarly,in a single charging process and a discharge process,the current density is set at equal intervals and the specific capacity is increased from 50 m A cm^-2 to 500 m A cm^-2 and then down to 50m A cm^-2 for testing.The results show that the charging voltage fluctuates within the range is-0.91～-1.21 V（vs.Ag/Ag Cl）,the discharge voltage fluctuation range is-0.74～-0.86 V（vs.Ag/Ag Cl）,and the coulombic efficiency is 93.85%,which once again proves the high rate performance.Cyclic tests with capacities of 100 m Ah cm^-2,150 m Ah cm^-2,and 200m Ah cm^-2 were carried out at a current density of 200 m A cm^-2.The average coulombic efficiency was all above 98%,indicating high cycle stability.When the current density is200 m A cm^-2 and the charge specific capacity is 200 m Ah cm^-2,the coulombic efficiency is 96.54%on average,and the discharge performance is very good.（3）The energy storage mechanism of the electrodes in the charging and discharging process was analyzed by in-situ microscope,and the morphological changes and synergistic effects of the multi-level structure were found.The morphology changes spontaneously during charging,the clusters,flakes,and granular structures play a synergistic role while absorbing Zn²⁺.The clusters and flakes with large specific surface area will preferentially grow,while the granular structure is stacked growth,which can be seen the flakes change to granular as they grow,and finally only clusters and granular structures are remained.During discharge,the peripheral clusters have a small specific surface area and high free energy,and will preferentially dissolve into Zn²⁺.The densely packed particles inside begin to dissolve into layers,and finally dissolve into small-sized flake structures.Assembled zinc-air battery for electrochemical test,the discharge performance is excellent,among which the physical test,especially the photoelectric conversion experiment,shows the significant advantages of the zinc-air battery based on the seawater system.