| The Aqueous rechargeable ion batteries have broad application prospects in power storage systems due to their merits of high safety,low cost,and environmental benignity.Among them,the aqueous zinc-ion battery stands out among many aqueous battery systems due to its inherent electrochemical characteristics,and is also known as a potential competitor that can break the existing electrochemical energy storage pattern dominated by traditional lithium-ion batteries.However,in addition to the challenge of poor reversibility of zinc anodes for aqueous zinc ion batteries,designing and de veloping cathode materials with high voltage,fast kinetics and stable cyclic cathode materials for the deintercalation of zinc ions are also the main factors restricting their development.The birnessite with large interlayer spacing has received extensive attention from researchers as the main structure of zinc ion deintercalation.This paper uses hydrothermal method to synthesize birnessite,further explores its reaction mechanism as a cathode material,and modifies the electrolyte to achieve high energy density and long cycle life of aqueous zinc ion batteries.(1)Using hydrothermal method to synthesize birnessite as the cathode material of zinc ion battery,the influence of different temperature and hydrothermal conditions on the crystallinity and morphology of birnessite was explored.Through experiments,it is found that in the appropriate temperature range,hydrothermal conditions can help increase the crystallinity of birnessite.In order to further explore the reaction mechanism and provide a better reaction substrate,samples with high crystallinity and uniform morphology under120°C hydrothermal conditions were taken for qualitative and quantitative analysis.The results showed that the chemical formula is Na0.1Mn O2·0.5H2O.(2)The mechanism of deintercalation of zinc ions from birnessite is studied by XPS,XRD and thermogravimetric analysis.XRD and XPS characterization of birnessite with different discharge depths were carried out to study the phase transition of birnessite during the reaction process and the determination of the embedded main body.At the same time,it combined with EDS and thermogravimetric analysis for verification and qualitative analysis.The results show that there are four water molecules that form coordination with zinc ions and co-intercalate into the main structure of birnessite.While the solvated water promotes the rapid diffusion of zinc ions,it also causes the hydroxylation of birnessite and the dissolution of manganese,resulting in birnessite.The collapse of manganese ore structure and rapid decay of capacity.(3)Modify the structure of the zinc ion solvation layer to change the zinc ion deintercalation reaction process and realizes the high energy density and long cycle life of the zinc ion battery.Urea,a strong ligand of zinc ions,is used to improve its solvation structure,and combined with XPS and hydrogen nuclear magnetic resonance,the solvation structure of zinc ions in different proportions of urea is assisted to simulate.Electroche mical characterization and experimental analysis of electrolytes with different ratios of urea to zinc ions,we found that when the ratio of urea to zinc ions is 1:3,a highly reversible[Zn(H2O)2(urea)3]2+complex can be obtained from water The sodium manganese crystal structure is embedded and released,and at the same time forms the cathode-electrolyte interface that inhibits the dissolution of Mn.In addition,on the anode side,the zinc ion solvation structure with an appropriate number of water molecules limits the activity of the water,ensuring the rapid diffusion of zinc ions,while inhibiting the generation of dendrites and"death-zinc"on the anode,thereby achieving a highly reversible Zinc anode.A full cell coupled with birnessite cathode and Zn metal anode delivers a discharge capacity of 270 m Ah g-1,a high energy density of 280 Wh kg-1,and capacity retention of 90%over 5000 cycles. |
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