Preparation And Sodium Storage Performance Of Bimetallic Selenide Based Composites

Sodium ion battery has abundant raw material reserves and high capacity,which makes it the most likely secondary energy storage battery to replace lithium-ion battery.However,the ion radius of sodium ion battery is larger than that of lithium ion,and it is easier to destroy the structure of active materials in the process of embedding and de embedding,resulting in the decline of material cycle stability.Therefore,the development of cathode materials with higher capacity and better stability is the focus of sodium ion battery research.Metal selenides have high theoretical capacity and large layer spacing,but their conductivity is poor,and large volume expansion will occur in the process of charge and discharge,resulting in poor cycle stability.In view of the above problems,this paper modifies metal selenides from the aspects of heteroatom doping,heterostructure construction and spatial structure design,so as to improve their electrochemical properties.（1）ZIF-8 dodecahedron was prepared by static method with zinc nitrate,2-methylimidazole and polyvinylpyrrolidone as raw materials.In this part,based on ZIF-8,Fe-Zn Se@NC nanostructures were prepared by Fe³⁺doping and selenidation.Zn Se has high capacity,the framework structure of ZIF can play a supporting role,and Fe ion doping can provide more active sites and improve the capacity of the battery.When the addition amount of Fe（NO₃）₃·9H₂O is 10 mg,the composite material had a capacity of 310 m Ah g^-1 at 100m A g^-1,and the capacity still maintained 280 m Ah g^-1 after 500 cycles at 1A g^-1.（2）In this part,Zn Se/Fe Se₂ bimetallic selenide heterostructure was synthesized by one-step hydrothermal method with zinc nitrate,iron nitrate and selenium dioxide as raw materials and hydrazine hydrate as reducing agent.Compared with single metal selenide,its capacity is higher.It is proved that the heterostructure between Zn Se and Fe Se₂ can improve the electrochemical performance,and it is determined that the optimal addition ratio of Zn source to Fe source is 1:2.On this basis,Zn Se/Fe Se₂-RGO composite was prepared.When the graphene concentration was 1 mg ml^-1,the performance of the composite was the best,and the capacity maintained 587.1m Ah g^-1 after 100 cycles at 100 m A g^-1.（3）Zn₃[Fe（CN）₆]₂ prussian blue analogue（Zn-Fe PBA）was prepared from zinc chloride,potassium ferricyanide and polyvinylpyrrolidone as precursors,and then Zn Se/Fe Se nanocomposites were prepared by seleniding.PVP as dispersant can adjust the morphology and structure of Zn-Fe PBA,thus affecting the electrochemical properties of Zn Se/Fe Se.Experiments show that when the amount of PVP is 0.6 g,the Zn Se/Fe Se nanocomposites have the best electrochemical properties and have a reversible capacity of 549.0m Ah g^-1 at 100 m A g^-1.This is due to the fact that the selenided Zn Se/Fe Se maintains the loose and porous structure of Zn-Fe PBA,which can relieve the volume expansion in the process,and the C-N bond can improve the conductivity of the material.