Preparation,Structure Design And Electrochemical Performance Optimization Of Composite Electrode Materials For Mangane-based Aqueous Zinc-ion Batteries

Zinc ion batteries（ZIBs）with mild aqueous electrolytes are receiving increasing attention because of their unique advantages such as low cost,environmental friendliness,ease of fabrication,and relative safety.Currently,for aqueous zinc ion batteries（AZIBs）,the development of a cathode material with excellent performance,stable structure and high capacity is a hot research topic.Among all the cathode materials for AZIBs,manganese-based compound cathode materials are one of the most promising materials for research with the advantages of abundant reserves,low cost,low toxicity,abundant valence and high zinc storage capacity.In recent years,manganese-based composites with various optimization strategies have been widely studied as the cathode materials for AZIBs.However,their development is hindered by their conductivity not reaching the theoretical value and poor cycle life.To improve this problem,in this paper,the electrochemical properties of the materials were improved by modifying their structure and surface.The main contents of this thesis are as follows:（1）Biphasic manganese oxide/manganese sulfide composite nanoparticles containing carbon coating were successfully synthesized as positive materials for AZIBs using hydrothermal and solvent thermal methods followed by high temperature sintering.The bi-directional heterogeneous structure formed a unique heterogeneous interface and increased the active sites.The highly hard carbon framework not only protects the structure of the electrode during battery charging and discharging,but also avoids direct contact between the active material and the electrolyte,which supplements the dissolution of the side reaction manganese ions and improves the cycle retention rate.The nanostructure shortens the diffusion path of ions in the crystal,endows more reaction sites,and accelerates the transport and diffusion of zinc ions,thus achieving high capacity and long cycle stability.The assembled battery has a capacity of 397.7 m Ah/g at a current density of 0.1 A/g.When the current density is increased to 5 A/g,the material still has a discharge capacity of 59.4 m Ah/g with excellent multiplicative performance.After 100cycles,the material still has a cycle retention rate of about 87%.The outstanding cycling and multiplicity performance is attributed to the protection of the material structure by the carbon framework and the biphasic heterogeneous structure that provides a heterogeneous interface and increases the active sites.This optimization strategy solves the problem of poor electrical conductivity of conventional manganese dioxide materials.（2）Hollow manganese dioxide nanospheres（hs-MnO₂@PDA）with polydopamine coating were successfully synthesized as positive electrode materials for AZIBs by the common sol-gel and hydrothermal methods after etching and then coating the conductive polymer on the material surface.On the one hand,the hollow structure and polymer coating buffer the huge volume change of the material during the material charging and discharging process,which makes the material structure more stable and thus improves the capacity retention of the material,and on the other hand,it can make the specific surface area of the material increase and have more active sites,which increases the electrochemical performance of the material.The synthesized materials exhibit good electrochemical performance with a discharge capacity of 365.8 m Ah/g at a current density of 0.1 A/g.The capacity retention rate was 95%after 100 charge/discharge cycles.Thanks to the excellent conductivity of the conductive polymer coating,the material still has a discharge capacity of 153.8 m Ah/g when the current density is increased to 2 A/g,exhibiting excellent multiplicative performance.This special structure combined with the conductive polymer coating strategy provides ideas for the future development of electrode materials...