Interfacial Coupling And Performance Of Vanadium-based Composite Cathode Materials For Aqueous Zinc-ion Batteries

Aqueous zinc ion batteries（AZIBs）are expected to be ideal devices for large-scale energy storage due to their advantages of low cost,high safety and high power density.Vanadium oxides with open layered structure are considered as ideal zinc storage materials.However,its low conductivity and weak structural stability,lead to rapid capacity attenuation and shorten the battery life in the cycle process.It is an effective way to improve the conductivity and structural stability of electrode materials to form heterogeneous structures by combining with highly conductive materials,in which the interface effect is a key factor to determine the structure and performance.Therefore,the influence of interfacial effects such as interfacial heterogeneous bonding,interfacial charge redistribution,and interfacial electric field on electrochemical performance and its behavior in charge/discharge process are studied by constructing two-dimensional heterogeneous materials with interfacial heterogeneous covalent bonding in this work.The main contents are as follows:1.V₅O₁₂·6H₂O nanosheets（HVO）were obtained by in-situ liquid phase growth exfoliation technique developed by ourselves,and the HVO surface was pretreated with positive charges.By electrostatic adsorption self-assembly with MXene nanosheets（Ti₃C₂）,two-dimensional heterostructural materials HVO@Ti₃C₂with V-O-Ti interface heterogeneous bonding have been obtained.The heterogeneous structure and Zn²⁺storage mechanism of HVO@Ti₃C₂are studied in detail by XPS,HRTEM,SEM,Raman,UPS,molecular orbital theory,coordination field theory and DFT calculation etc.It is found that HVO@Ti₃C₂exhibits a dynamic and reversible interfacial coupling during the discharge/charge process,that is,the insertion/extration of Zn²⁺during discharge/charge is accompanied by reversible breaking/reconstruction of the interfacial V-O-Ti bond.The interfacial heterobond（V-O-Ti）prevents the irreversible oxidation of Ti₃C₂during the first charge.This two-dimensional dynamic heterogeneous interface coupling behavior activated the Faraday activity of MXene which originally has no capacity contribution in AZIBs,making it an additional electron receiver/donor,providing extra capacity contribution beyond the theoretical capacity of HVO.At the same time,this reversible structural change forms"interfacial buffering"to preserve the integrity of the material,thus increasing the cycle life.Therefore,when HVO@Ti₃C₂is used as the cathode material of AZIBs,the ultra-high specific capacity of 457.1 m Ah·g^-1at 0.2 A·g^-1(over 600 m Ah·g^-1based on HVO mass and exceeding the theoretical capacity of HVO)and the high capacity retention rate of 88.9%after 1000 cycles at 5.0 A·g^-1are achieved.The construction of two-dimensional dynamic heterogeneous interface coupling provides a new design idea for the study of electrode materials and a feasible scheme for the realization of high energy density and high cyclic stability of AZIBs.2.Based on the design idea of two-dimensional heterogeneous structure,we replace MXene with graphene oxide（GO）,which is rich in oxygen functional groups and has a lower price.By a simple hydrothermal method,GO nanosheets were used as the base and the surface group（-O）was used as the nucleation site to induce the preparation of folded sheet HVO@GO 2D heterogeneous materials.It was found that the oxygen functional groups on the surface of GO also have similar effects to the oxygen functional groups on the surface of MXene,and can also be used as bridging atoms to form V-O-C interfacical heterobond.At the same time,the construction of interfacial coupling can effectively improve the conductivity of the material and increase the diffusion coefficient of Zn²⁺(10^-9～10^-11cm²S^-1),so that it has the ability to adapt to the high current density of rapid insertion/extration,thus giving HVO@GO electrode more excellent rate performance than HVO@Ti₃C₂and HVO electrode.