Surface Modification And Electrochemical Performance Study Of Zinc Anode For Zinc Ion Batteries

Zinc ion batteries（ZIBs）with aqueous electrolyte have significant advantages in cost,safety and environmental protection,making them one of the promising next generation of large-scale energy storage devices.Among them,the zinc metal anode has received extensive attention due to its high theoretical capacity(mass capacity of 820m Ah g^-1,volumetric capacity of 5855 m Ah cm^-3)and low reduction potential（-0.762V vs.SHE）.However,there are still many problems and challenges to the development of ZIBs,among which the irreversible dendrite growth and the side reactions caused by water decomposition on the zinc metal anode are particularly prominent.To address these problems,this thesis designs three multi-functional zinc anode protection means to inhibit both dendrite growth and side reactions through surface modification of the anode with modified layer,and improves the electrochemical performance of the zinc anode and investigates its mechanism.Based on the deposition reaction of Zn²⁺and MoO4^2-,the ZnMoO4 modified layer was constructed in situ on the surface of metallic zinc.The ridge-like structure of the ZnMoO4 modified layer and its high zinc binding energy can effectively promote the uniform deposition and dissolution of zinc.In addition,the deposition and dissolution of zinc in the"valley"of the modified layer avoids the transmembrane transport of Zn²⁺and supports the high multiplicity cycling of anode.Combined with the highΔGH*of ZnMoO4（1.16 e V）,the modified layer can simultaneously inhibit the growth of dendrites and the occurrence of side reactions,achieving a stable high multiplicity cycling of the zinc anode at 1.0 m A cm^-2 and 1.0 m Ah cm^-2 for 2000 h.The deposition and dissolution of zinc in the"valley"of ZnMoO4 modified layer will affect the regulation of the modified layer on subsequent zinc deposition and dissolution under higher surface capacity cycling conditions,resulting in Zn@ZnMoO4anode limited stable cycle capacity.Inspired by the host and guest interaction,squaramide derivative host that can capture SO4^2-guest in the electrolyte was designed and prepared as a surface modification material for the anode.The hydrogen bonding effect of the squaramide derivative containing-NH group on SO4^2-makes the modified layer negatively charged,and the resulting electrostatic interaction can effectively disperse Zn²⁺to inhibit the growth of dendrites,while the attraction of Zn²⁺can also accelerate the migration of Zn²⁺.At the same time,the negatively charged modified layer can repel the SO4^2-in the electrolyte,and in combination with the highΔGH*of 1.32 e V of the complex,the hydrogen evolution becomes difficult and the generation of（Zn SO4）·（Zn（OH）2）3·x H2O by-products is significantly inhibited.The zinc anode has an ion mobility number of 0.76 and a Coulomb efficiency of 99.1%.A single ex-situ rigid modified layer is difficult to adapt to the volume change of the zinc anode under cycling,a bilayer artificial SEI modified layer is constructed on the anode surface（outer layer:squaramide derivative-doped PVA gel;inner layer:ZnMoO4-PVA hybrid layer）.The PVA outer layer can play an adhesive role to improve the mechanical stability of the modified layer under high surface capacity cycling.Meanwhile,the squaramide derivatives in PVA can trap SO4^2-in the electrolyte and enhance the migration of Zn²⁺.The ZnMoO4 in the inner layer can inhibit the formation of dendrites and the occurrence of side reactions,and the Zn²⁺fast pathway generated at the interface between ZnMoO4 and PVA can further accelerate the Zn²⁺migration.The maximum charge/discharge current density of the zinc anode reaches 10.0 m A cm^-2.