Study On Stability Regulation And Mechanism Of The Zn Anode/Electrolyte Interface In Aqueous Zinc-Ion Batteries

Owing to the inherent properties of high safety,low cost and low toxicity,aqueous zinc-ion battery is considered as the potential alternative for the large-scale energy storage system.However,Zn anode suffers fromthe dendtrite growth,hydrogen evolution and corrosion,which limit the electrochemical performance of aqueous zinc-ion battery.Uneven zinc ion deposition is caused by the changes in the surface structure of the metal zinc electrode after charge-discharge,hydrogen evolution and corrosion reactions,which can greatly reduce the Coulombic efficiency of zinc-ion batteries.Therefore,it is necessary to understand the transport mechanismof zinc ions at the zinc anode/electrolyte interface,which is beneficial for improving the stability of the interface and interfacial charge uniformity.This is the key to the uniformdeposition of zinc and the inhibition of the growth of zinc dendrites for improving the performance of the zinc anode.In this thesis,by constructing artificial solid electrolyte（SEI）membranes,optimizing electrolytes,and designing and preparing gel electrolytes,the stability of the zinc anode/electrolyte interface is enhanced,and the charge at the interface is uniformly distributed,thereby improving the performance of aqueous zinc-ion batteries.This Ph.D.thesis works in enhancing the cycle-life and Coulombic efficiency of zinc-ion batteries can provide a theoretical basis for promoting their industrial applications.The main research contents and research results of this thesis are as follows:（1）The ordered transport of zinc ions is realized by introducing a perovskite nano-Ba Ti O₃ artificial SEI filmthat can spontaneously adjust the interfacial electric field.Ba Ti O₃ can be polarized by the internal electric field of the battery,resulting in directional dipoles whose polarization direction changes with the direction of the applied electric field.During the deposition of zinc ions,Ba Ti O₃ can spontaneously generate a uniforminterfacial electric field at the zinc anode/electrolyte interface to guide the orderly deposition of zinc ions.In addition,due to electrostatic repulsion,a certain of sulfate ions are blocked out of the Ba Ti O₃ artificial SEI film,reducing its interfacial contact with Zn ions and Zn anode,thereby improving the Coulombic efficiency of Zn anode deposition/dissolution.The Zn symmetric battery assembled based on this Ba Ti O₃ artificial SEI filmcan operate for 2000 hours at a current density of 1 mA cm^-2 and a capacity density of 1 mAh cm^-2.When matched with manganese dioxide cathode,the Coulombic efficiency is still close to 100%after 300 cycles at a current density of 2 A g^-1.（2）The hydrogen evolution reaction and the growth of zinc dendrites are inhibited by the supramolecular host-guest interaction at the zinc anode/electrolyte interface.18crown ether 6 serves as the scavenger of H₃O⁺.18 crown ether 6 as the host and H₃O⁺in 2 M Zn SO₄ aqueous solution as the guest enable the host and guest ions at the interface to have recognition property,thereby inhibiting the electrochemical reactivity of H₃O⁺and alleviating the hydrogen evolution reaction occurred on the surface of the zinc anode.At the same time,the host-guest complex of 18 crown ether 6 and H₃O⁺can adsorbe on the surface of the zinc anode,resulting in an electrostatic shielding effect,thereby inhibiting the growth of zinc dendrites.Under the protection of 18 crown ether6,the Zn//Zn symmetric battery can operate for 2000 hours at a current density of 1.4mA cm^-2 and a capacity density of 1.4 mAh cm^-2;when the current density and capacity density are increased to 6 mA cm^-2 and 6 mAh cm^-2,respectively,this symmetrical battery can also operate for 500 hours.After 280 cycles at a current density of 500 mA g^-1,the Zn//Na mixed-ion battery using a Prussian blue derivative of sodiumas the cathode can still achieve a Coulombic efficiency close to 100%and a capacity of 89%.（3）The interfacial zinc ion transport is successfully regulated by the hydrophilic small molecule xylitol.During the zinc deposition process,xylitol can be adsorbed on the protruding tip of the zinc anode surface formed by the uneven deposition.On the one hand,it acts as an electrostatic shield and inhibits the growth of zinc dendrites;on the other hand,it forms hydrogen bonds with water to alleviate hydrogen evolution reaction.In the 1 M Zn（CH₃COO）₂ electrolyte with the xylitol concentration of 0.02 g L^-1,the Zn//Zn symmetric battery can exhibit a cycling life of 300 hours at a current density of 1 mA cm^-2 and a capacity density of 1 mAh cm^-2.（4）The solvation structure of zinc ions is regulated by the crowded environment of high concentration macromolecular dextran in the electrolyte.The high concentration of macromolecular glucan in the electrolyte can cause a volume exclusion effect,occupying most of the space,and forming a local high concentration environment for other electrolyte salts.Based on this,in 1 M Zn Cl₂ electrolyte,the crowded environment caused by high concentration of dextran and its steric repulsion force can change the solvated structure of zinc ions,transforming the solvated structures of Zn（H₂O）₆²⁺into Zn Cl₄^2-and other solvated structures,thus inhibiting the hydrogen evolution reaction and hindering the growth of zinc dendrites.Using this electrolyte,the Zn//Zn symmetric battery can be cycled for 540 hours at a current density of 1 mA cm^-2 and a capacity density of 1 mAh cm^-2.（5）The concentration of zinc ions is regulated at the molecular scale by using pseudopolyrotaxane as a hydrogel electrolyte.This pseudopolyrotaxane hydrogel is formed by the self-assembly of poly（ethylene oxide）（PEO）andα-cyclodextrin（CD）in aqueous solution,which enables the adsorption of zinc ions in the region constructed by CD and PEO.The uniformconcentration of regionalized zinc ions is achieved at the molecular scale,subsequently,the concentration polarization of zinc ions between the electrode and electrolyte is reduced.Thus,the uniformdeposition of zinc ions is achieved,thereby inhibiting the growth of zinc dendrites.Based on pseudopolyrotaxane as the electrolyte,the Zn//Zn symmetric cell can present a cycling life of 1370 hours at a current density of 0.7 mA cm^-2 and a capacity density of 0.7 mAh cm^-2.The Coulombic efficiency of the Zn//Cu half cell remains around 100%after 116 cycles at0.5 mA cm^-2 and 0.5 mAh cm^-2.