Synthesis Of Copper Vanadate Nanomaterials And Study On The Performance Of Aqueous Zinc-ion Battery

In recent years,due to the environmental problems caused by the energy crisis and the burning of fossil fuels,the search for alternative clean energy has become the focus of global research.Despite the high energy density of lithium-ion batteries,safety is still a common problem,which has hindered the application of lithium-ion batteries in large-scale storage devices.Aqueous zinc ion battery uses neutral and cheap aqueous electrolyte to ensure the safety of the system.At the same time,the cost of zinc metal is low,and it has low polarizability and multi-electron transfer ability.It can provide high specific capacity and energy density,so it has potential application prospects.Compared with lithium ions,zinc ions have a large molecular weight and are difficult to deintercalate ions.Therefore,the suitable cathode materials for zinc ion batteries are relatively rare.In this paper,copper vanadate is used as the cathode material of water-based zinc-ion batteries to explore its electrochemical performance.The main research findings are as follows:(1)The Cu V₂O₆nanowire material was synthesized by a simple hydrothermal method,assembled into an aqueous zinc-ion battery,and its electrochemical performance was tested.Observed by scanning and high-resolution transmission electron microscopy,the nanowires has a length greater than 10?m and a width of 100?200 nm,and grows preferentially along the c-axis.Ex-situ characterization by XRD and XPS found that the intercalation/deintercalation of zinc ions during the first electrochemical cycle will cause a reversible phase transition of the Cu V₂O₆structure and transform it into a Zn_xV₂O₅·n H₂O phase.At the same time,a new type of replacement mechanism was discovered:the intercalation/extraction of zinc ions can lead to a reversible reduction/oxidation reaction of copper ions.The replaced metal copper element improves the conductivity of the electrode material,thus showing excellent electrochemical performance:At a current density of 200 m A g^-1,the first discharge capacity of Cu V₂O₆nanowire electrode material can reach about 338 m Ah g^-1;at a current density of 5 A g^-1,after 1200 cycles,the specific capacity is still 143 m Ah g^-1,and the capacity retention rate is close to 100%.(2)Using polyvinylpyrrolidone as a surfactant,copper nitrate and acetylaceton vanadyl oxide as raw materials,a hydrothermal synthesis method was used to prepare Cu_0.95V₂O₅nanoflowers materials composed of nanosheets.Observed by transmission and high-resolution electron microscopy,the nanosheets are smaller than 200 nm in size and grow preferentially along the c-axis direction.Ex-situ XRD and XPS also found a partially reversible copper ion reduction/oxidation displacement reaction mechanism.During the first insertion/extraction of zinc ions,part of the irreversible extraction of copper ions leads to a phase change of Cu_0.95V₂O₅to a coexisting phase of Cu_0.4V₂O₅and Zn₃(OH)₂V₂O₇·2H₂O,therefore,excellent electrochemical performance is obtained:At the current density of 5 A g^-1,the specific capacity still has?200m Ah g^-1after 1000 cycles,and the capacity retention rate is 92%.