Interfacial Regulation And Stabilization Mechanism Of Zn Anode In Aqueous Zn Ion Batteries

Aqueous zinc ion batteries（ZIBs）have become a focused research object in the field of energy storage due to their low cost,high safety,and green environment.However,Zn anode is prone to hydrogen evolution and side reactions in weakly acidic or neutral electrolytes,leading to excessive consumption of metal Zn and electrolytes which reduces the reversibility of the reaction and results in low Coulombic efficiency.Meanwhile,the formation of Zn dendrites will penetrate the separator and create a short circuit in the cell,giving rise to significant safety problems.The above-mentioned issues with the Zn anode have seriously hampered the industrialization of ZIBs.Given this,the thesis systematically studies and analyzes the interface regulation of the Zn anode.The main contents are as follows:（1）Inorganic mesoporous Ti O₂ material is prepared by hydrothermal method and coated on the surface of Zn anode using a spin coating process to build an artificial interface,where the optimal thickness of the coating is 20μm and the coating displays completeness and homogeneity on the surface of the Zn anode.Meanwhile,the modified Zn anode exhibits the lowest interfacial impedance in a symmetric cell and can be stably cycled for 500 h at 4.4 m A cm^-2/1.1 m Ah cm^-2.The link between the effect of the coating on the ion transfer kinetics at the anode-electrolyte interface and the electrochemical performance is further investigated.It is found that ion transfer at the interface is divided into the coating-electrolyte interface and the ion transfer behavior inside the coating.At the coating-electrolyte interface,density functional theory（DFT）shows that the binding energy of Zn to Ti O₂ is higher than that of pure Zn,which facilitates the rapid transfer of interfacial ions to the coating surface.In the coating,Zn²⁺displays the lowest migration energy barrier inside（100）of the Ti O₂,and the mesoporous structure effectively shortens the ion transfer path.Therefore,the mesoporous Ti O₂ coating effectively promotes ion transfer kinetics at the anode-electrolyte interface and improves the electrochemical performance of the Zn anode.（2）The organic gel material is prepared by dissolving starch and coated on the surface of the Zn anode to construct an interfacial coating,in which the organic starch has excellent mechanical properties and a more complete and compact coating than the inorganic material.The modified anode is also stabilized in a symmetric cell for over 3300 h at 0.5 m A cm^-2/0.25 m Ah cm^-2.The effect of the transfer behavior of interfacial ions within the starch coating on the cycling performance of the Zn anode is further investigated.It is found that the strong interaction between the internal hydroxyl groups of starch and Zn²⁺could induce uniform Zn deposition and effectively buffer the formation of Zn dendrites,thus enabling the preparation of Zn anodes for long-life aqueous Zn-ion batteries.（3）A simple and efficient electrodeposition method is used instead of the spin coating to construct a zinc-nickel（Zn Ni）alloy interface with stronger bonding to the Zn matrix,where the optimum thickness of the layer consisting of Ni₅Zn₂₁ alloy particles is 4.1μm and the layer displays excellent structural and chemical stability.Concurrently,the Zn anode can be stably cycled for over 500 h at a high current density and a low areal capacity(20 m A cm^-2/2 m Ah cm^-2).The effect of the Zn Ni alloy layer on the homogeneous nucleation of Zn is further explored based on the relationship between the inhomogeneous nucleation of pure Zn anode and the formation of initial Zn dendrites.It is found that the Ni in the alloy has an excellent affinity to Zn which promotes the homogeneous nucleation of Zn around the coating instead of continuing to build up nucleation on the surface of the original Zn nuclei,thus buffering the formation of Zn dendrites.As a result,the Zn Ni alloy interface enables the development of ultra-fast charging and cyclically stable Zn anode.（4）The zinc-phosphorus（Zn P）alloy interface is prepared using electrodeposition,where the Zn P coating with an intact and compact surface is composed of Zn P solid solution alloy and an optimum thickness is 1.7μm.At the same time,the Zn anode can be stably cycled for over 300h at a high current density and high areal capacity(20 m A cm^-2/30 m Ah cm^-2,depth of discharge,DOD=52%).The effect of Zn P alloy coating on interfacial ion transfer kinetics is further analyzed.It is found that the non-metallic phosphorus in the alloy has a better affinity to Zn,indicating that the coating can effectively improve the interfacial ion transfer kinetics.And the coating can decrease the electrochemical reaction energy barrier by fitting the Arrhenius equation,suggesting that Zn²⁺can efficiently participate in the electrochemical reaction process after rapid transfer to the interface.Meanwhile,an intact and compact Zn P coating facilitates the mitigation of hydrogen evolution and side reactions.Therefore,the Zn P coating improves the reversibility and DOD of the Zn anode,enabling the preparation of ultra-fast charging and high DOD for the Zn anode.（5）The Zn foil is etched with HCl to construct a three-dimensional（3D）trench structure of surface defects,where the surface defects formed after 20 s of etching in 4 M HCl show a more regular and complete morphology.Meanwhile,the Zn anode with the introduced surface defects can be stably cycled for over 1300 h at 1 m A cm^-2/0.5 m Ah cm^-2.Based on the influence of the inhomogeneous Zn plating/stripping behavior of pure Zn anode on Zn dendrite formation,the mechanism of surface defects affecting the homogeneous Zn plating/stripping behavior is further investigated.Finite element simulations and experiments show that the etched surface has a lower current density,which effectively regulates the Zn plating/stripping behavior,buffering dendrite growth and further extending the cycle life of the Zn anode.Thus,direct modification of the Zn matrix to introduce surface defects greatly improves the cycle life of the Zn anode and is more beneficial to the energy density of the battery than artificial protective layers.（6）In combination with conventional metal fabrication processes,the Zn foil is quenched after annealing at 400°C for 3 h to introduce 3D nano-protrusions of surface defects and internal vacancy clusters.Under the synergistic effect of surface defects and internal defects,Zn nuclei are uniformly formed on the surface of the quenched Zn foil,and the Zn anode could eventually stably cycle for 1700 h at 2 m A cm^-2/1 m Ah cm^-2.It is found that the surface defects reduce the Zn nucleation barrier and the interfacial impedance.The molecular dynamics simulations and experimental results show that the internal vacancy clusters can effectively bind the adsorbed-state Zn atoms,avoiding the uneven nucleation caused by the aggregation of adsorbed-state Zn atoms along with the two-dimensional diffusion of the electrode surface.Therefore,synergistic surface and internal defects lead to a dendrite-free Zn anode with a stable interface.