Syntheses And Lithium-storage Properties Of Graphene Aerogel/Prussian Blue Derivatives

In recent years,the development of lithium-intercalation materials with large capacity and excellent cycle stability has afforded lithium-ion batteries(LIBs)with vigorous applications from portable electronic products to electric vehicles and smart grids.Nevertheless,the design and synthesis of LIBs anode materials with high energy density and long cycle life is still a hot spot for researchers.Prussian blue analogues(PBAs)derived materials(metal oxides,metal selenides)have an open framework structure,rich redox active sites and other characteristics,which are expected to replace traditional anode materials.However,the poor conductivity of such materials and the inevitable volume expansion during the cycling and other shortcomings resulted in the low specific capacity of electrode materials.This thesis aimed at improving the electrical conductivity of PBAs-derived materials and the volume effect during the cycles.Graphene aerogel(GA)is used as the substrate to combine with PBAs by the encapsulating effect.Then,the obtained PBAs@GA was calcined at a high temperature to prepare a series of composite electrodes of PBA derivatives and GA.These materials were employed as flexible self-supporting anodes for LIBs.On the basis of the basic characterizations and electrochemical performance tests,the relationship between the compositions,various structural parameters and their electrochemical performances were revealed.The research contents are as follows:(1)The FeCo-PBA nanocubes were wrapped into the network of GA substrate by a solvothermal method.Then,the FeCo-PBA@GA precursor was selenized to prepare the FeCoSe₂@GA composite with encapsulated structure and used as self-supporting anode materials for LIBs.Compared with pure FeCoSe₂ and GA electrode materials,the FeCoSe₂@GA composite electrode showed an excellent electrochemical performance.The specific capacity of the composite electrode was 496mAhg^-1 after100 cycles when the current density is 100mAg^-1.The outstanding lithium-storage properties can be attributed to the unique network structure of GA,which provides a large number of ion exchange channels,and effectively alleviated the agglomeration phenomenon and volume expansion effect of metal selenide nanoparticles during the cycles.(2)A solvothermal approach was used to wrap MnFe-PBA nanocubes into the network of GA,and then a high-temperature selenization process was applied to obtain the MnFeSe@GA composite with encapsulating structure,which was employed as a self-supporting anode for LIBs.The results showed that the synergistic effect between bimetal selenide and GA endowed the composite electrode with a superior lithium storage performance.When the current density was 100mAg^-1,the specific capacity of the composite electrode could still reach 843mAhg^-1 after 120cycles.The excellent electrochemical performance was mainly attributed to the unique three-dimensional network structure of GA substrate,which significantly improved the agglomeration effect and inevitable volume expansion of metal selenide nanoparticles during the charge and discharge process.(3)With GA as the substrate,the bimetallic NiCo-PBA nanoparticles were encapsulated in the GA network by a solvothermal method.Subsequently,the Ni Co-oxide@GA composite with encapsulation structure was obtained after a high-temperature calcination,which was used as the flexible self-supporting anode materials for LIBs.The results demonstrated that the composite electrode exhibited a superior electrochemical performance to pure GA or bimetallic oxides,benefiting from the inherent structural characteristics of bimetal oxides and their synergistic interaction.After 100 times of cycles at a current density of 100mAg^-1,the specific capacity of the composite was as high as 721mAhg^-1,which benefited from the synergistic effect between GA and bimetal oxides.