Study On Bismuth Selenide For Energy Storage And Modification Of Sodium Ion Battery

Due to its high abundance and low price,sodium has attracted much attention in the research of sodium ion batteries.However,because the atomic radius of sodium ions is larger than that of lithium ions,the layer spacing with graphite as the negative electrode cannot support the smooth deintercalation of sodium ions.The topological insulator materials represented by Bi₂Se₃have excellent surface conductivity due to its special surface state.Although its transport properties have attracted much attention,the application field needs to be broadened,and its application in the field of electrochemical energy storage is few reported.Bi₂Se₃is a 2D layered material combined with van der Waals forces.Its interlayer spacing is much higher than that of graphite.Combined with its high surface conductivity,it is expected to become a high-rate,high-specific capacity sodium ion battery negative electrode material.However,due to the various energy storage reactions of Bi₂Se₃,its volume changes drastically during charging and discharging.The pulverization and shedding of Bi₂Se₃resulting in rapid degradation of battery specific capacity.Therefore,the problem of long-period stable charging and discharging of electrodes needs to be solved urgently.This article takes the improvement of the cycle stability and specific capacity of Bi₂Se₃as the purpose,adopts the methods of constructing heterostructures and coatings,respectively.Then,systematically studies the effects of heterostructure and nanostructure design on the material microstructure and energy storage characteristics.The rules of influence are as follows.Bi₂Se₃precursors were prepared by hydrothermal method,combined with rapid annealing in the air to construct Bi₂Se₃/Bi₂O₃heterostructures.Different from the preparation of Bi₂O₃precursor by hydrothermal method followed by selenization in a tube furnace,this method significantly reduces the amount of selenium powder used and the time cost of material preparation and effectively improves the synthesis efficiency of the material.In addition,Bi₂Se₃can provide fast carrier transport channels.Bi₂O₃has a high theoretical specific capacity,which can increase the specific capacity of composite materials.When it is used as the negative electrode of a sodium ion battery,the Bi₂Se₃/Bi₂O₃electrode maintains a specific capacity of 310m Ah/g after 100 cycles of charging and discharging.Under the same conditions,the specific discharge capacity of the Bi₂Se₃and Bi₂O₃electrodes is only 35 and 158m Ah/g,respectively.To improve the cycling stability of Bi₂Se₃,this article uses atomic layer deposition technology（ALD）to uniformly coat the outside of Bi₂Se₃with a nano-thick amorphous Ti O₂layer（the thickness of 150 cycles of Ti O₂is about 4 nm）.This design not only takes advantage of the regulation of the electronic structure at the heterointerface but also combines the good chemical/electrochemical stability and excellent mechanical properties of the Ti O₂coating layer,which can effectively withstand the volume expansion of Bi₂Se₃,thereby improving the Bi₂Se₃composite electrode stability.Benefiting from the advantages of heterostructure and Ti O₂coating layer,the specific capacity of Bi₂Se₃/Ti O₂composite electrode can reach385.6 m Ah/g,and it still maintains 281.4 m Ah/g after 400 charge and discharge.The above-mentioned methods for structural design and stability optimization of high-volume variable electrode materials provide experimental reference and feasibility reference.