Carbon-Modification And Electrochemical Properties Of V₂O₅ Cathode Material For Aqueous Zinc-Ion Batteries

The rapid development of industrial technology not only brings people a high quality of life,but also puts forward higher requirements for energy storage system.Lithium-ion battery has become the most widely used rechargeable battery because of its high energy density,but it has some problems such as high manufacturing cost and poor safety.Therefore,it is very necessary to develop a new type of green sustainable energy system.In recent years,water zinc ion battery has been recognized as an excellent substitute for lithium ion battery in the field of portable devices and wearable electronics because of its low cost,high capacity and good safety.At present,the development of water system zinc ion battery is mainly limited by cathode materials,so it is particularly important to develop cathode materials suitable for water system zinc ion battery.In this paper,carbon elements rich in natural sources were selected to modify commercial V₂O₅.Graphite modified V₂O₅cathode materials,carboxylated CNTs modified V₂O₅cathode materials and organic carbon modified V₂O₅cathode materials were prepared.Their structures,morphologies and compositions were characterized by X-ray powder diffractometer（XRD）,scanning electron microscope（SEM）and X-ray energy dispersive spectroscopy（EDS）.The electrochemical properties were tested by constant current charge-discharge test（GCD）,cyclic voltammetry（CV）and electrochemical impedance spectroscopy（EIS）.The specific experimental contents and results are as follows:（1）The commercial V₂O₅was modified with inexpensive graphite.The prepared graphite-modified V₂O₅（V₂O₅@C）was nanoparticles with an average particle size of 23.5 nm and a specific surface area of 19.336 m²/g.The addition of grahite did not change the crystalline structure of V₂O₅,but enhanced the conductivity of V₂O₅.The aqueous Zn-ion battery assembled with V₂O₅@C as the cathode exhibits a specific capacity of 350.29 m Ah/g at a current density of 2.0 A/g,and the capacity retention rate is about 88%after 600 cycles.The particle-size refinement increases the specific surface area of V₂O₅,enables the electrolyte and guest ions to fully penetrate into the electrode to participate in the electrochemical reaction,thereby increases the specific capacity of the V₂O₅@C cathode.The ion deintercalation mechanism of Zn//V₂O₅@C battery was analyzed by CV test.（2）V₂O₅was modified with carboxylated CNTs with high electrical conductivity and high mechanical stability.The prepared carboxylated CNTs-modified V₂O₅（V₂O₅@CNTs）nanoparticles had an average particle size of 27.4 nm and a specific surface area of 13.037m²/g.The aqueous zinc-ion battery with V₂O₅@CNTs as the cathode has a specific capacity of350.56 m Ah/g at a current density of 2.0 A/g,and a specific capacity of 308.16 m Ah/g after400 cycles,with a capacity retention rate of about 92%.The addition of CNTs enhanced the electrical conductivity of V₂O₅which greatly improved the cycling stability of the battery.（3）Using citric acid（CA）with containing carboxyl and hydroxyl groups and PEG-400（M4）with hydroxyl groups as organic carbon sources,V₂O₅@CA nanorods and V₂O₅@M4 micro rod,and explored the formation mechanism of V₂O₅@CA and V₂O₅@M4microrods have been synthesized.Compared with commercial V₂O₅cathodes,organic carbon-modified V₂O₅cathodes have higher electrolyte and guest ion diffusivity in batteries because of the larger specific surface（improved morphology 11.23 m²/g,6.32 m²/g）areas of V₂O₅@CA and V₂O₅@M4,and the grain size is smaller（27.3 nm and 21.7 nm,respectively）,so they can have 91%and 96%capacity after 500 cycles at a current density of 2.0 A/g,respectively.retention rate.