Construction Of Dendrite-free Zinc Metal Anode And Its Application In Aqueous Zinc Ion Battery

Lithium-ion batteries（LIBs）are one of the most widely used energy storage devices and have received much attention for their relatively high energy density and cycling stability.However,their limited lithium resources and the use of flammable organic electrolytes have stimulated the search for reliable alternatives.Among the many metal ion batteries,aqueous zinc ion batteries（AZIBs）have been favored by researchers due to their economic benefits and environmental friendliness.More importantly,zinc metal has abundant resource reserves,high theoretical capacity,and good chemical stability,and has the potential for large-scale energy storage applications.Despite these significant advantages,dendrite growth and hydrogen precipitation corrosion reactions occurring during the cycling process of zinc anodes greatly shorten the service life of AZIBs and cannot meet their practical applications.In this thesis,we focus on three aspects of zinc anode surface modification,electrolyte optimization and diaphragm modification to achieve dendrite-free zinc anodes,aiming to improve the overall performance of AZIBs.（1）Strontium titanate nanoparticles（Sr Ti O₃）were mainly investigated as a protective layer to enhance the electrochemical performance of zinc metal anodes.The specific scheme is to construct a highly adaptive protective layer（Zn@Sr Ti O₃）on Zn anode by doctor casting method from Sr Ti O₃ nanoparticles and polyvinylidene fluoride（PVDF）matrix.On the one hand,the PVDF matrix exhibits excellent mechanical flexibility and acts as an elastic restraint and barrier layer,which can suppress additional interfacial reactions and dendrite evolution.On the other hand,Sr Ti O₃ nanoparticles with dielectric properties can retune the zinc electrodeposition behavior by adjusting the polarization electric field distribution.Physical characterization and electrochemical results show that the artificial Sr Ti O₃ coating is significantly thinner than other reported Zn anode protection layers,greatly shortening the ion migration path.In addition,this Zn@Sr Ti O₃symmetric cell and full cell exhibit excellent cycling stability and multiplicative performance.The enhanced reversibility of Zn plating/exfoliation can be seen by the Coulomb efficiency and cyclic voltammetry test results.（2）The main study investigated the mechanism of the contribution of maize alcohol soluble protein coated filter paper diaphragm to the cyclic stability of zinc anode.the abundant positive and negative functional groups on Zein can reduce the proton activity in weakly acidic Zn（CF₃SO₃）₂ aqueous solution electrolyte,thus inhibiting the corrosion reaction and hydrogen precipitation process.Also,Zein interacts with zinc ions and CF₃SO₃^2-taniodns,thus modifying their transport.Based on these advantages,the symmetrical Zn cell using the Zein-modified filter exhibited excellent long-term cycling performance of more than 600 h at a current density of 1 m A cm^-2 and an area capacity of 1 m A h cm^-2（the original cell was less than 50 h）.In addition,the electrochemical performance of the Zn||Mn O₂ full cell was improved,with a more stable capacity retention of about 40.3%after 200 cycles at 500 m A g^-1.（3）Adding polyvinylpyrrolidone（PVP）molecules as additives to the Zn（CF₃SO₃）₂ is to limit the growth of Zn dendrites and improve the cycle life of AZIBs.A small amount of PVP additive can regulate the ion flux distribution by combining the N atom on the pyrrolidone group with zinc to form a Zn-N structure in situ.The small molecule PVP layer adsorbed on the Zn surface can prevent the direct contact between Zn metal and electrolyte,while increasing the hydrogen precipitation potential and thus inhibiting the corrosion caused by free water decomposition.In addition,the small molecule PVP layer can homogenize the local electric field at the electrode interface,avoiding the preferential accumulation of zinc ions under high electric field concentration,regulating the uniform deposition of zinc ions,and thus inhibiting zinc dendrites.Experimental results show that the symmetric cell with PVP addition can be cycled for 200 h at a high current density of4 m A cm^-2,and the capacity retention of the full cell is increased after 200 cycles at a current density of 1 A g^-1.These excellent electrochemical properties indicate the potential application of low-cost and convenient PVP additives.