Preparation And Modification Of Prussian Blue Analogues And Its Application In Sodium Ion Battery

With the growing application of lithium ion battery in the portable hardware and electric vehicles or other fields,the demand of lithium increases rapidly.Lithium reserves are limited and uneven distribution,which will greatly restrict the sustainable development of lithium ion batteries in the fut ure.Compared with lithium,sodium has similar physical and chemical properties and is rich in reserves.Therefore,the research on sodium ion batteries,especially cathode materials,is of great importance.Prussian blue materials w hich is low cost and environmental friendly has attracted wide attention owing to its three-dimensional structure of tunnel and the foreground of industrialization.Now there are still many problems to be solved,such as the control of crystallization water,uniformity,conductivity,and so on.In this paper,Prussian blue materials were prepared and modified,which were tested and analyzed under different application scenarios of organic and aqueous systems.Then compare and select the locally optimal solutions.The Prussian blue analogue Na_x MFe?CN?₆?M=Fe?Cu?Ni?Mn?were prepared by co-precipitation with same proportion but different types of transition metals The Na₂Fe Fe?CN?₆ has the best overall performance and was selected as precursor material.By using the co-precipitation method,chemical vapor deposition,single iron source method to synthesis Na₂Fe Fe?CN?₆,which showed different morphology and electrochemical properties.The results show that the material prepared by single iron source method is a better choice,whose grains have clear edges and very regular cube structure,and the size distribution between 200 nm-600 nm,and the consistency is the best.Under the current density of 0.1 C,constant charge discharge test was carried out,the maximum charge-discharge capacity reached 144 m Ah·g^-1,and the capacity retention rate was 98%after 100 cycles under 0.2 C current density.On the basis of the above results,GO was prepared by Hummers method,and the carbon doped Na₂Fe Fe?CN?₆@GO was prepared by ultrasonic dispersion i n Na₄Fe?CN?₆ aqueous solution.PB particles adhere to the framework of graphene oxide to form a conductive network with excellent structure.Compared with pure phase PB,the conductivity and structural stability of PB@GO are significantly improved,thus ensuring the rate and cycle performance of the material.Under the charge-discharge rate of 1 C,the specific capacity in the organic system was maintained at 120 m Ah·g^-1after 200 cycles,and the reversible specific capacity was 71 m Ah·g^-1after 130 cycles in the aqueous system.The capacity retention rate were both above 95%.Through screening different transition metal ions to determine the precursor material Na₂Fe Fe?CN?₆.Comparing different preparation processes,we concluded that most reasonable method is single iron sources method.Furthermore Na₂Fe Fe?CN?₆ doped with GO could improve the rate performance in organic and aqueous system.Finally,the industrial application value of this material was verified.