Study On Interfacial Modification Of Zinc Anode/Electrolyte For Aqueous Zinc Ion Batteries

Aqueous zinc-ion batteries are expected to be applied to large-scale energy storage systems for their high safety,high energy density and low cost.However,there are some problems such as zinc dendrite growth and side reaction at the zinc anode/electrolyte interface,which make the cycling life and coulombic efficiency of zinc anode poor.The modification of the zinc anode/electrolyte interface is of great significance to improve the electrochemical performance of zinc anode and promote the application and development of aqueous zinc-ion batteries.In this paper,the zinc anode/electrolyte interface is modified by adding electrolyte additives and constructing an artificial interface layer on the surface of zinc anode to inhibit the growth of zinc dendrites and the occurrence of interface side reaction,so as to improve the stability and reversibility of zinc anode.The main findings are as follows:（1）Citric acid,tartaric acid,ascorbic acid organic molecular additives were used to optimize the electrolyte of 2 M Zn SO₄ for aqueous zinc-ion battery,and then modified the zinc anode/electrolyte interface to improve the electrochemical performance of zinc anode.Among them,ascorbic acid additive has the best modification effect on the interface and its rich hydroxyl groups enable it to be adsorbed on the surface of zinc anode,increasing zinc nucleation sites,which is conducive to inducing uniform deposition of zinc and inhibiting the growth of dendrites at the zinc anode/electrolyte interface.Ascorbic acid molecules can also weaken the interaction between Zn²⁺and water molecules,changing the solvation structure of Zn²⁺and reducing the occurrence of interfacial side reaction.Based on this,in 2 M Zn SO₄ electrolyte containing 0.01 M ascorbic acid additive,the zinc anode showed good electrochemical performance,and the assembled symmetric cell showed a cycling life of 1400 h at 1 m A cm^-2 with 1 m Ah cm^-2.When the current density increased to 10 m A cm^-2,only 40 m V was polarized and showed excellent electrochemical kinetics.The average coulombic efficiency of assembled Zn||Cu half-cell was 99.2%at 1 m A cm^-2 for 100 cycles,indicating that ascorbic acid additive effectively improved the electrochemical stability and reversibility of zinc anode.（2）V₄C₃T_x and V₂CT_x were prepared by HF etching,and the vanadium-based MXene artificial interface layer was constructed on the surface of the zinc anode.Vanadium-based MXene artificial interface layer,especially V₂CT_xMXene,blocks the direct contact between metal zinc and electrolyte,slowing down the occurrence of side reactions such as corrosion and hydrogen evolution at the interface.It also inhibits the passivation of the zinc anode surface by inert by-products in order to reduce the interfacial charge transport impedance,and provides abundant zinc nucleation sites,reduces the two-dimensional diffusion time of Zn²⁺on the zinc anode surface for inducing uniform deposition of zinc,effectively inhibits the formation and growth of zinc dendrites and significantly improves the electrochemical performance of zinc anode.Therefore,the symmetric cell assembled with zinc anode modified by V₂CT_x MXene artificial interface layer can be stable for more than 700 h at 10 m A cm^-2 with 1 m Ah cm^-2,showing good stability.The assembled Zn||Cu half-cell was stable for 1000cycles at 10 m A cm^-2 and the average coulombic efficiency reached 99.5%,showing excellent zinc deposition/dissolution reversibility.Matching it with the V₂O₅ cathode material,assembled full cell was cycling for 1000 cycles at 2 A g^-1 and the capacity retention rate was as high as 88.11%,indicating that the vanadium-based MXene artificial interface layer could effectively optimize the zinc anode/electrolyte interface,thereby improving the stability of the zinc anode.（3）Aimed at the problem that the hydrophilic end group on the surface of V₂CT_x MXene caused its inhibitory effect on side reactions to be improved,PVP was used as the intercalator to modify V₂CT_x MXene,and PVP-V₂CT_x was constructed as an artificial interface layer on the surface of zinc anode.The polymer hydrocarbon chain in the PVP molecule makes the artificial interface layer of PVP-V₂CT_x hydrophobic,which further hinders the direct contact between the water molecules in the electrolyte and the metal zinc anode,effectively avoiding the occurrence of interface side reactions and greatly improving the reversibility of the zinc anode.In addition,PVP intercalation also expands the layer spacing of MXene to promote the transport of Zn²⁺,which is conducive to promoting zinc deposition uniformly on the surface of zinc anode and inhibiting the growth of zinc dendrites.Based on the above characteristics,the symmetric cell assembled with zinc anode modified by PVP-V₂CT_x artificial interface layer showed a stable cycle of 230 h under the conditions of 10 m A cm^-2 and 10 m Ah cm^-2.In particular,its assembled Zn||Cu half-cell can be stable for 4000 cycles and exhibits extremely high average coulombic efficiency（99.85%）.The full cell assembled with V₂O₅ cathode material retains 209.3m Ah g^-1 after 600 cycles at the current density of 2 A g^-1,indicating that the PVP-V₂CT_x artificial interface layer can make the zinc anode show good stability and excellent deposition/dissolution reversibility.