Research On Cathode Materials For Aqueous Zinc-ion Batteries Based On Prussian Blue Analogs

Currently,aqueous rechargeable batteries based on multivalent metal ions such as Mg²⁺,Zn²⁺,and Al³⁺have received more and more attention in the field of energy storage.Aqueous batteries use environmentally friendly aqueous electrolytes,which have higher safety than organic batteries,and have shown great development potential in large-scale power grid energy storage.Among various aqueous energy storage systems,aqueous zinc-ion batteries（AZIBs）have attracted extensive research interest due to the advantages of zinc’s high theoretical specific capacity,low redox potential,low cost and environmental friendliness.The current cathode materials of AZIBs mainly include manganese-based materials,vanadium-based materials,Prussian blue analogs（PBAs）,etc.These cathode materials usually have problems such as slow diffusion kinetics of Zn²⁺and material dissolution in electrolytes.Therefore,the design of new cathode materials with excellent zinc storage performance is the key to the current research on AZIBs.PBAs are a kind of competitive cathode materials,their ideal three-dimensional open structure can realize rapid intercalation or deintercalation of Zn²⁺,and they have the advantages of high operating voltage and simple synthesis method.However,these materials have poor electrical conductivity and are prone to structural collapse during cycling.These disadvantages affect the zinc storage capacity of these materials.In order to deal with the above problems,this work uses Prussian blue analogs as active materials,selects different types of carbon materials（two-dimensional,one-dimensional and zero-dimensional）to composite with them in order to improve the overall conductivity and stability of PBAs electrodes,and then boost their zinc storage properties.For the obtained series of PBAs-based cathode materials with good energy storage properties,and the morphology and structure of the materials were analyzed by various characterization methods.The electrochemical properties of the materials were studied,and the zinc storage mechanisms of the materials were further explored.The details are as follows:（1）We develop a new PBAs-based composite cathode material for AZIBs by loading uniform nickel hexacyanoferrate（Ni HCF）nanocubes onto two-dimensional reduced graphene oxide（RGO）sheets.In the Ni HCF/RGO composite,Ni HCF nanoparticles are well anchored on the RGO layers,forming a conductive network.The strong synergy between Ni HCF and highly conductive RGO effectively increases the specific surface area,accelerates the electron and ion transport,and inhibits the structural collapse of the Ni HCF/RGO electrode during the Zn²⁺insertion/extraction process.Benefiting from the above advantages,the Ni HCF/RGO composite exhibits a remarkable reversible capacity of 94.1 m Ah g^-1 at a current density of 5 m A g^-1,excellent rate performance of 52.3 m Ah g^-1 at 200 m A g^-1,and good cycling stability(94.1%capacity retention after 1000 cycles at 200 m A g^-1).（2）Vanadium hexacyanoferrate（VHCF）nanoparticles were grown on one-dimensional carbon nanotubes（CNTs）by using a simple in situ co-precipitation method.This composite structure of VHCF nanoparticles and CNTs improves the conductivity of the material by introducing the conductive skeleton of CNTs,which promotes the electron transport between VHCF nanoparticles and effectively improves the utilization of electrode materials.Benefiting from the inherent sufficient channels for ions insertion/extraction of VHCF and improved electrical conductivity,the VHCF/CNTs composite as AZIBs cathode material shows excellent zinc storage performance with a high reversible capacity of 97.8 m Ah g^-1 at 50 m A g^-1.The discharge specific capacity is still as high as 52.7 m Ah g^-1 after 1000 cycles at 3200m A g^-1.（3）A composite cathode material was prepared and applied to AZIBs by in-situ growing manganese hexacyanoferrate（Mn HCF）in the presence of zero-dimensional nitrogen-doped carbon dots（NCDs）,in which the carbon dots well modified the Mn HCF active material.The introduced NCDs significantly improved the overall conductivity and structural stability of the composites,and also provided abundant active sites for electrochemical reactions.Benefiting from the above advantages,the Mn HCF/NCDs composite electrode material exhibits good electrochemical zinc storage capacity,including high discharge specific capacity(131.2 m Ah g^-1 at 50 m A g^-1)and excellent cycling performance(almost no capacity decay after 1000 cycles of charging and discharging at 1000 m A g^-1),which is significantly better than that of the pure Mn HCF material.In this paper,the VHCF/CNTs composite prepared in chapter 3 is the first to be used in aqueous zinc-ion batteries,and the method of introducing nitrogen-doped carbon dots into AZIBs cathode material in chapter 4 is also novel to improve its zinc storage performance.This work provides several simple and effective methods for constructing high-performance PBAs-based cathode materials for AZIBs.