Polymer Surface Moldification For High-performance Zn Metal Anodes

With the increasing consumption of non-renewable energy sources such as fossil energy,finding alternative green energy storage and transfer equipment has become a research hotspot.Lithium-ion batteries have been widely used in portable electronic devices due to their high specific capacity and potential,such as mobile phones,personal computers,digital cameras,and electric cars.However,Lithium-ion batteries have many hidden safety hazards,such as:flammable,explosive,and electrolyte leakage.And the lack of lithium resources leads to high cost problems,which further limits the application of Lithium-based batteries in many fields.Therefore,it is an urgent to find a new alternative battery system.Aqueous Zinc(Zn)-based batteries have attracted widespread attention because of their large power density and energy density,and attractive prospects for future application.The resources of Zn are abundant,chemically stable,etc.Also,it has suitable electrochemical windows in near-neutral and mild acid electrolytes,which are very suitable for the application of large-scale energy storage equipment.However,there are many problems with Zn metal anodes:(1)The zinc plating/stripping process will inevitably form dendrites,especially in the long cycle process.(2)Hydrogen evolution reaction is likely to occur due to the influence of thermodynamic and kinetic factors.(3)When the hydrogen evolution reaction occurs,the local OH-concentration of the Zn anode will increase,and OH-will react with Zn2+to form an insoluble inorganic compound attached to the surface of the Zn anode,causing passivation and increased battery internal resistance.To solve these problems above,there are the following strategies:(1)Surface modification,to restrain the growth of Zn dendrite by coating the surface of the Zn anode with a protective layer by in-situ or ex-situ methods.(2)Structural design,to get homogenous Zn deposition by designing 3D structural current collectors or metal organic framework substrates(MOF).(3)Select appropriate electrolyte,including using different Zn salts,appropriate electrolyte concentrations,electrolyte additives,or using a hydro-gel electrolyte to deduce side reactions.In this context,we have designed and studied the surface modification of Zn metal anodes by two polymer materials,which modulate the morphology of Zn surface and enhance the electrochemical properties of aqueous Zn-ion batteries.The main contents are as follows(1)Using polypyrrole to protect Zn metal anode as the-NH group on the surface of the polypyrrole will coordinate with Zn2+,reducing the two-dimensional diffusion of Zn2+.We successftully synthesized rod-shaped polypyrrole by chemical polymerization,which was further deposited on the surface of Zinc metal anode by simple casting coating method.The conductive polypyrrole frame coating will greatly improve the electric field distribution on the surface of the Zn anode,so that Zn2+ can be uniformly deposited on the surface of the Zn anode.After half-cells and full-cells are constructed and tested,the polypyrrole modified Zn anode can greatly enhance the electrochemical performance of the battery,especially for long-term cycling(2)Using polypyrrole-co-polyaniline copolymer to protect Zn metal anode as its better conductivity and mechanical flexibility.What is more,was prepared by chemical polymerization of pyrrole and aniline.The groups on the surface of the copolymer will coordinate with Zn2+,reducing the number of nucleation sites of Zn2+,thereby modulate the morphology of Zn.We successfully synthesized rod-shaped polypyrrole by chemical polymerization,which was further deposited on the surface of Zinc metal anode by simple casting coating method.The conductive copolymer modifies the electric field distribution on the surface of the Zn anode,promotes the reaction kinetics,and eventually causes the deposited Zn to "lie" on the surface of the Zn anode horizontally.This special deposition behavior greatly reduces the risk of battery short circuits.After assembling half-cells and full-cells,it has been tested that the copolymer-modified Zn anode can significantly improve the electrochemical stability of the batteries.It is also confirmed that polymer modified Zn anode is indeed a simple and effective protection strategy.