Preparation Of Metal Selenides And Hybrid Anode Materials And Study On Energy Storage Behavior

Due to the abundant storage of sodium resources and low cost,the sodium ion capacitor has gradually replaced the lithium ion capacitor which is short of resources.However,a large number of anode materials used for lithium ion storage lead to a slow insertion/extraction rate of Na⁺due to a large radius of Na⁺,limiting the cycling stability and rate capability of sodium ion capacitors.Therefore,it is crucial to find an ideal anode material for sodium storage.Due to their inexpensive cost,high-voltage platform,and high theoretical capacity,metal selenides have garnered considerable attention.However,its volume expands drastically and even collapses structurally during charge/discharge processes.In this paper,different metal selenides and their composites were prepared to explore the storage behavior of sodium ions.Specific research work is as follows:（1）SnSe was prepared by electrostatic self-assembled,and rich mesoporous carbon layers encapsulated SnSe nanosheets via covalent bonds（SnSe@C）were prepared with dopamine hydrochloride as carbon source.Carbon layer as a conductive matrix can not only accelerate electron transfer,but also effectively limit the volume expansion of SnSe and promote the stability of the structure.At the same time,the carbon layer also acts as a physical barrier to reduce the dissolution of Na₂Se and selenide in the electrolyte.After 110 cycles at 0.1 A g^-1,SnSe@C maintaines a specific capacity of 211.3 m Ah g^-1.The specific capacity is up to 210.1 m Ah g^-1at5.0 A g^-1.SnSe@C//AC sodium ion capacitor can reach the energy/power density of66.7 Wh kg^-1/200 W kg^-1,with a capacity retention rate of 71.4%after 1000 cycles.（2）Ti₃C₂coated SnSe（SnSe@Ti₃C₂）with three-dimensional network structure was prepared by electrostatic self-assembled and annealing process to alleviate the structural collapse and adverse reaction kinetics of SnSe caused by Na⁺storage.First,SnSe with conversion and alloying reaction mechanism provides extremely high specific capacity.Second,the three-dimensional network structure of Ti₃C₂greatly alleviates the volume change and stacking problems of SnSe nanosheets during Na⁺insertion/extraction.Ti₃C₂also provides a large number of transfer paths and reactive sites for Na⁺,while providing fast three-dimensional conductive channels for charge transfer.SnSe@Ti₃C₂possesses a highly reversible capacity of 240.1 m Ah g^-1at 0.1 A g^-1,maintaining a capacity retention rate of 108.7%after 1350 cycles.When the current density is up to 5.0 A g^-1,the specific capacity can reach 128.6 m Ah g^-1.The capacity retention rate of SnSe@Ti₃C₂//AC sodium ion capacitor is 73.8%after 10000cycles at 1.0 A g^-1.（3）Ti₃C₂and carbon layer coated Fe Se₂（Fe Se₂@C/Ti₃C₂）was prepared by hydrothermal method and selenization strategy.First,the initial specific capacity is increased by Fe Se₂.Second,the aggregation/restacking between Ti₃C₂nanosheets are suppressed by Fe Se₂@C.A large number of functional groups and open pores of Ti₃C₂provide abundant reactive sites and convenient transfer channels for Na⁺.Finally,the carbon layer and Ti₃C₂on the one hand,as the protective layer,greatly improve the structural integrity of Fe Se₂,reduce the dissolution of Na₂Se in the electrolyte.On the other hand,the carbon layer and Ti₃C₂,as the conductive matrix,provide a fast conductive path for the charge transfer.Fe Se₂@C/Ti₃C₂with sandwich structure shows a high capacity of 220.9 m Ah g^-1after 410 cycles at 1.0 A g^-1.When the current density is up to 5.0 A g^-1,the specific capacity can reach 182.0 m Ah g^-1.The capacity retention rate of Fe Se₂@C/Ti₃C₂//AC sodium ion capacitor is 70.4%after1650 ultra-long cycles at 1.0 A g^-1.Based on the above research,the cycle stability and rate capability of metal selenide are improved greatly through the compound optimization.The coated protective layer,such as carbon layer and Ti₃C₂,can effectively inhibit the structure collapse of metal selenide and the dissolution of active substances in the electrolyte.The feasibility is verified by structural characterization and testing.This provides a new idea for the research and development of stable anode materials.