Study On The Design Of Three-dimensional Skeleton-assisted Electrodes And Its Effect On The Stripping Behavior Of Zinc Deposition On Metallic Zinc Anodes

Aqueous zinc ion batteries are considered to be the most promising key devices for large-scale electrochemical energy storage systems due to their high safety and low cost characteristics,and have been rapidly developed in recent years.As the biggest obstacle to the practical application of aqueous zinc ion batteries,the zinc cathode has a significant impact on the battery lifetime and cycle efficiency,and the development of highly stable and dendrite free zinc cathodes is the key to the commercialization of aqueous zinc ion batteries.So far,there are two main categories of research on metallic zinc anodes:two-dimensional and three-dimensional.Two-dimensional zinc foils usually suffer from severe structural damage due to large volume changes in repeated deposition/exfoliation behavior;three-dimensional structured anodes have low Coulombic efficiency and poor reversibility,so there is an urgent need to develop new high efficiency dendrite free zinc anode materials.Zinc anode structure design,as an effective zinc anode modification strategy,can effectively improve the deposition behavior of zinc ions,but there are still problems such as unstable deposition behavior,low Coulomb efficiency and serious side reactions.To address the above problems,this paper presents a modified design of different three-dimensional conductive carbon skeletons based on three-dimensional structure design and zincophilic improvement strategies as zinc anode auxiliary electrodes to further optimize the zinc deposition stripping behavior of zinc anode,mainly as follows:（1）A cotton fiber framework modified by copper acetate gradient was prepared by infiltration soaking method,and then carbonized and reduced simultaneously at high temperature by reduction carbonization method to successfully produce a carbon fiber skeleton modified by copper nanoparticles（Carbonized filter paper@Copper nanoparticles,CFP@Cu）inheriting the characteristics of copper acetate gradient distribution.CFP@Cu consists of interwoven carbon fibers with a diameter of 5μm and a thickness of about 41μm.The copper nanoparticles with a diameter of 7-20 nm are uniformly distributed on the fiber surface,and their distribution density decreases from the dense bottom layer to the surface layer,with a gradient distribution in the vertical plane.When it is used as an auxiliary electrode for the anode of zinc ion batteries,it exhibits high cycling stability,coulombic efficiency and low polarization voltage.The assembled symmetric cells operate stably for more than 1800 h under the operating conditions of 10 m A·cm^-2,2 m Ah·cm^-2,and the assembled asymmetric cells have an average of 600 cycles under the operating conditions of 1 m A·cm^-2,1 m Ah·cm^-2Coulombic efficiency as high as 99.51%,also played a good stabilization role in zinc deposition/exfoliation behavior observation experiments.The excellent stabilization of zinc deposition/exfoliation is attributed to the electric field homogeneity of its conductive backbone and the adsorption of gradient pro-zinc copper nanoparticles.The clever gradient distribution pattern effectively guides the uniform deposition of zinc ions,and the addition of pro-zinc sites effectively improves the efficiency of zinc deposition/exfoliation and enhances the reversibility.（2）PAN/PVP hybrid fiber membranes containing copper acetate and zinc acetate were prepared by electrostatic spinning,followed by carbonization to prepare carbon fiber skeletons（Cu O/Zn O-NCFs）with copper oxide and zinc oxide nanoparticles embedded on the fiber surface.The diameter of carbon fibers obtained by electrostatic spinning is about 150 nm,and the interlaced and dense porous carbon fiber skeleton provides sufficient space for zinc deposition.The densely distributed Cu O and Zn O particles as pro-Zn sites greatly reduce the barriers to zinc formation and make zinc deposition more uniform.The Cu O/Zn O-NCFs exhibit excellent modification of zinc deposition stripping behavior when used as an auxiliary electrode for Zn-ion batteries,and the assembled symmetric cells have an ultrahigh cycle life(stable operation over 4000 h at 0.5 m A·cm^-2,0.25 m Ah·cm^-2)and excellent ability to reduce local current density(Only 53 m V polarization voltage at 10 m A·cm^-2,10 m Ah·cm^-2 operating conditions and 180 hours of stable operation).The excellent and stable homogeneous zinc deposition/exfoliation behavior is mainly due to the large number of strong pro-zinc sites,which greatly attract the deposition of zinc ions,resulting in a uniform distribution of zinc ion deposition,effectively suppressing the generation of dendrites and ensuring the cycle life.