Investigations On Surface Modification And Electrolyte Additive For Zn Metal Anode

Zinc ion batteries are considered to be ideal candidates due to environmental friendliness,abundant resources,good safety and low cost for large-scale energy storage.Nevertheless,zinc metal anode still suffers from serious challenges,such as zinc dendrites and by-products at present.These problems resulted in poor cycle performance,low material utilization rate and safety issues,which severely restrict the commercialization of water-based zinc ion batteries.Hence,it is necessary to exploit a kind of effective strategies to the modification of Zn anode so that suppressing the formation of dendrite,alleviating side reactions,thereby improving the Coulombic efficiency and cycle stability of batteries.Two strategies of interface engineering and the optimization of electrolyte was proposed to modify the Zn anode.The main work of this paper includes:1.Base on interface modification engineering,constructing functional nitrogen-doped carbon networks（N-C）coating layer on zinc anode,which realized the dendrite-free Zn stripping/plating and long cycle life.N-C are obtained by facile hydrolysis-high temperature calcination method using pyrrole monomer as starting materials,then it was coated on the surface of the Zn anode.On the one hand,the coating layer preventing the directly contact between the zinc metal anode and the electrolyte,further alleviating side reactions.On the other hand,the good conductivity of the N-C coating can lower nucleation overpotential and alleviate the dendrite growth caused by the"tip effect".As a consequence,the as-prepared N-C/Zn anode displays superior cycling stability with cycle life of 800 h at a current density of 2 m A cm^-2with the capacity of 2 m Ah cm^-2.Furthermore,a steady Coulombic efficiency of 98.76%was acquired at 2 m A cm^-2,which is higher than the pristine Zn anode.What’s more,the N-C/Zn||V₂O₅full battery delivers high discharge capacity of 162.10 m Ah g^-1at 2 A g^-1after 500 cycles and long cycle life.2.Based on the electrolyte design,Ti₃C₂T_xMXene was used as electrolyte additive to in-situ constructing conductive and functional interface layer on the surface of Zn anode,which realized the dendrite-free Zn stripping/plating.MXene interfacial layer with abundant functional groups and good conductivity induces uniform nucleation and enables long-term even deposition.Moreover,MXene sheets can dramatically shorten Zn²⁺diffusion pathways in electrolyte,facilitate their migration and well accommodate the surface structure change due to the excellent elasticity of MXene interfacial layer.Electrochemical performance test show that the Zn anode presents stable cycling performances of more than 1180 cycles at 2 m A cm^-2,as well as high Coulombic efficiency of nearly 100%with the assistance of MXene additive.The as-fabricated Zn||V₂O₅full cell with MXene added electrolyte also displays high specific capacity of326.4 m Ah g^-1at 1 A g^-1after 300 cycles.3.Based on the electrolyte design,2-methylimidazole was used as electrolyte additive to constructing Zinc（II）-2-methylimidazole coordination compound film,relieving side reactions and realizing long cycle life.On the one hand,the preparation of Zinc（II）-2-methylimidazole coordination compound film can prevent the directly contact between the zinc metal anode and the electrolyte,which significantly inhibits the formation of zinc dendrite.On the other hand,utilizing specific kinds of anions and molecules to regulate the coordination environment of Zn²⁺and H₂O.This changes in the coordination environment of Zn²⁺reduces the diffusivity of ions and increases the nucleation overpotential,thereby leading to uniform deposition morphology,inhibiting the side reactions.