Study On The Preparation Of Several Layered Materials And Their Lithium/zinc Storage Performances

At present,both lithium ion batteries and zinc ion batteries are effective energy storage and conversion devices.Among them,the research and development of electrode material is an important driving force for the rapid development of battery technologies.Therefore,this paper focuses on the syntheses and electrochemical performances of layered structure electrode materials for lithium ion and zinc ion storage systems,including molybdenum-based material,vanadium-based materials and carbon-based materials.The detailed research content includes the following four parts:Firstly,we successfully prepared the NaVMoO₆ cathode material for lithium ion batteries using the sol-gel method,and studied its electrochemical performance for the first time.Owing to the stable quasi-layered structure of the Na VMo O₆ material,the Na VMo O₆ electrode exhibits good cycling performance(at a current density of 5 m A g^-1,after 50 cycles,the reversible specific capacity of the Na VMo O₆ electrode sustains 126.4 m Ah g^-1).The results of ex-situ X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS)analysis indicate that Na in Na VMo O₆ material only serves as a"pillar"to stabilize the Na VMo O₆ structure;while both V and Mo in Na VMo O₆ material participate in electrochemical reaction,contributing to the capacity.The ex-situ XRD result reveals that during the electrochemical reaction,the working mechanism of the NaVMoO₆ cathode material is the intercalation reaction.Secondly,we used bottom-up wet chemical method to synthesize M@C₂N(M=Ru,Pd and Co)materials,and investigated their lithium ion storage performances in detail for the first time.In the M@C₂N material,metals(M=Ru,Pd,and Co)are uniformly embedded in the two-dimensional C₂N structure.Their unique structural features(such as uniform two-dimensional nanopore structure and large specific surface area)endow the M@C₂N electrodes with excellent lithium storage performances,including good rate performances(at a current density of 1 C,the specific discharge capacities of Ru@C₂N,Pd@C₂N and Co@C₂N electrodes are 413.9,340.6 and 333.4 m Ah g^-1,respectively,and the discharge specific capacities at 5 C are 290.6,199.3 and 239.0 m Ah g^-1,respectively)and stable cycling performances(45.0%,46.2%,and 41.8%initial capacity retention after 200 cycles for Ru@C₂N,Pd@C₂N and Co@C₂N electrodes,respectively).Overall,this research work can provide an important reference information for the development of high-performance carbon-based anodes.Thirdly,using the hydrothermal reaction method,we successfully prepared a typical ammonium vanadium bronze(NH₄V₄O₁₀)material with nanosheet structure.In order to enhance the zinc ion storage performance of the NH₄V₄O₁₀ electrode,we optimized the proportion of conductive carbon in the NH₄V₄O₁₀ electrode for the first time.The research results show that the addition of the appropriate amount of conductive carbon can not only alleviate the dissolution problem of NH₄V₄O₁₀ material,but also build a good conductive"bridge"connecting the NH₄V₄O₁₀ material and the electrolyte,so that the NH₄V₄O₁₀ electrode can achieve the better cycling performance and rate performance.Ex-situ XRD proves the reaction mechanism of Zn²⁺/H⁺co-insertion/extraction for the NH₄V₄O₁₀ electrode,while ex-situ XRD and XPS analysis results show that NH₄⁺in NH₄V₄O₁₀ does not participate in the electrochemical reaction of zinc ion storage(acting as a"pillar").In short,the optimized process of electrode preparation can provide new idea for the development of high-performance advanced zinc ion storage system.Fourthly,for the purpose of improving the electronic conductivity and ionic diffusion coefficient of material,we have successfully designed the zinc ion batteries cathode material NH₄V₄O₁₀@C with the higher electronic conductivity and the larger Zn²⁺diffusion coefficient.Benefiting from the significant enhancement in electronic conductivity and ionic diffusion coefficient,the NH₄V₄O₁₀@C electrode delivers not only outstanding rate capability(even under the condition of 10 A g^-1,it still keeps a specific capacity of 227.4 m Ah g^-1),but also excellent cycling stability of up to 3000 cycles.We hope that this research work could enrich the design systems of cathode materials for zinc ion batteries to meet the development needs of zinc ion batteries with the higher rate capacity,the longer cycle life and the better safety characteristics.