Study On Vanadium Disulfide And Manganese Dioxide As Cathode Materials For Aqueous Zinc-Ion Batteries

Faced with the existing problems of environmental pollution,energy crisis and global warming,the development and utilization of renewable,economic and clean energy has become an important way to solve this problem.Lithium-ion batteries are widely used because of their high energy density and high output voltage.However,limited lithium resources and safety issues influenced its large-scale production and application scenarios.Aqueous Zn-ion batteries have the advantages of large capacity,non-toxic,safety,environmental protection,simple manufacturing process and low cost,becoming a promising candidate replacing lithium-ion batteries.Vanadium-based and Manganese-based materials have been used as positive electrodes,due to their wide ion storage space,abundant valence changes and high capacity.In this paper,layered-based VS₂ and tunnel-based structures ofα-MnO₂ were designed,and their electrochemical properties as cathode materials for aqueous zinc ion batteries were studied.The main research contents and results are as follows:1.The layered D-VS₂ material with abundant lattice defects was synthesized by a simple one-step hydrothermal method.The results of structural characterization show that the material has larger surface area and pore size due to the existence of abundant defects.Compared with VS₂-200 material with high crystallinity,D-VS₂ material displays higher discharge specific capacity(discharge specific capacity of 156.3 mAh g^-1,when the current density is 100 mA g^-1)and excellent rate capacity(when current density is 1000 mA g^-1,discharge specific capacity can achieve 123.4 mAh g^-1).The improvement of electrochemical performance may be due to the fact that abundant defects increase the storage sites and diffusion paths of ions in the crystal.The electrochemical reaction mechanism of reversible insertion/（de）insertion of Zn²⁺and H⁺in the crystal structure during charging and discharging process was demonstrated by ex-situ tests.2.α-MnO₂@C-N nanorod was synthesized by in-situ coating method.Carbon coated film can not only effectively improve the conductivity of electrode materials,but also buffer the structural strain during repeating charge and discharge.Due to the good synergistic interaction betweenα-MnO₂ and the carbon coating film,the electrochemical performance ofα-MnO₂@C-N shows that the specific discharge capacity of 334 mAh g^-1 and good structural stability（71.5%capacity retention after 2000 cycles）.The electrochemical energy storage mechanism ofα-MnO₂@C-N nanorods shows that Zn²⁺and H⁺are embedded into the crystal structure during the discharge process,andα-MnO₂@C-N transforms to ZnMn₂O₄ and MnOOH.After fully charged,ZnMn₂O₄ and MnOOH undergo incomplete transformation.The contents of ZnMn₂O₄ and MnOOH in the cathode accumulated during the cycles,andα-MnO₂@C-N,ZnMn₂O₄ and MnOOH may act as storage carriers for ions in the subsequent charging and discharging process.