Structural Design Of Bismuth/Cobalt/Iron Metal Sulfide And Selenide Materials And Their Applications In Energy Storage

With the global climate problem,the consumption of non-renewable energy and the increase of people's demand for energy,the development of a clean energy storage system has attracted the increasing attention of researchers.Lithium-ion batteries have been successfully used in commercial electronic products in the past years due to their lightness,portability,and high energy density.However,the uneven distribution and limitation of lithium sources increase the cost and limit the wide application of lithium ion batteries.The sodium and potassium elements belong to the same main group with l ithium element,meanwhile the sources of sodium and potassium elements are rich and they are widely distributed in earth.Therefore,sodium and potassium ion batteries have great potential to be used in electronic devices.However,anode materials used for lithium ion batteries are not completely suitable for sodium ion batteries and potassium ion batteries.Therefore,the rational design of high energy density anode materials for SIBs and PIBs is a key factor to promote the development of new batteries.The anode materials of alloy-conversion mechanism and conversion mechanism have high energy density,which have application potential for SIBs and PIBs,especially bismuth-based,cobalt-based,iron-based and other sulfur/selenium compounds.For example,the theoretical specific capacities of Bi2S3 and FeS2 are 625,894 mAh g-1,respectively.However,those materials also have problems such as volume expansion and the side reactions in traditional carbonate electrolytes during the electrochemical reactions,which affect the specific capacity and cycle stability of the materials.The volume expansion of Bi-based materials is an obstacle for application.In this thesis,the performances of anode materials are improved mainly through the structure design,carbon material composite and electrolyte optimization.The main research contents are listed as follows:(1)Controllable preparation of dandelion-like Bi2S3/rGO microspheres and their electrochemical performances for potassium ion batteries and sodium ion half/full cells.The dandelion-like Bi2S3/rGO hierarchical microspheres materials were prepared by a hydrothermal process.The size of Bi2S3/rGO microspheres is in the range of 2-9?m.When Bi2S3/rGO was used as anode for potassium ion batteries,the discharge capacity remains at 206.9 mAh g-1 at 100 mA g-1 after 1200 cycles.When it was used as anode for sodium ion batteries,it also shows superior electrochemical performances.In addition,sodium ion full cell of Na3V2(PO4)3@rGO//Bi2S3/rGO was successfully assembled and the reversible specific capacity was maintained at 129.9 mAh g-1 after 60 cycles at a current density of 100 mA g-1.The structural design of the material,the uniform compounding of carbon materials and the synergistic effect of the electrolyte,etc.make the material exhibit excellent electrochemical performances in SIBs and PIBs.(2)Space-confined growth of Bi2Se3@NC composite as anode for potassium ion full/half cells and lithium ion batteries.Bi2Se3@NC was synthesized by hydrothermal reaction and calcination process at high temperature,the size was concentrated with?500 nm.When it was applied as anode for potassium ion batteries,the discharge capacity was remained at 201.2 mAh g-1 after 1200 cycles at current density of 100 mA g-1.When current density is 1000 mA g-1,the reversible specific capacity remains at 130.5 mAh g-1.In addition,potassium ion full cells were assembled successfully by matching Bi2Se3@NC with cathode material PTCDA-450 and the discharge capacity was maintained at 122.3 mAh g-1 after 200 cycles at 100 mA g-1.Bi2Se3@NC as anode for lithium ion batteries also shows excellent performances.The relationship between the structural advantages and electrochemical performances of Bi2Se3@NC was explored by density functional theory calculations.In addition,the electrochemical reaction mechanism of Bi2Se3@NC as anode for potassium ion batteries were explored through ex-situ XRD combined with HRTEM.(3)Controllable preparation of CoSe2/C nanospheres and their electrochemical performances for sodium ion full/half cells and potassium ion full/half cells.Yolk-shell structured CoSe2/C nanospheres were prepared by hydrothermal and subsequent selenization processes.The size of the nanospheres is uniformly distributed at 500 nm.When the yolk-shell structured CoSe2/C used as anode for sodium ion batteries,the reversible capacity remained at 312.1 mAh g-1 after 1600 cycles at 4 A g1.When CoSe2/C acted as anode for potassium ion batteries,its specific capacity was matained 369.2 mAh g-1 at 50 mA g-1.At the same time,sodium ion full cells(CoSe2/C//Na3V2(PO4)3@rGO)and potassium ion full cells(CoSe2/C//PTCDA-450)were successfully assembled,and both of full-cells show excellent performances.CoSe2 particles are embedded in the carbon-based material to enable good conductivity while effectively inhibiting the agglomeration of active materials.The reasonable design of the structure plays an important role in improvement of electrochemical performances.(4)Synthesis of porous hollow P-doped FeS2 nanospheres and their electrochemical performances for potassium ion full/half cells.The P-doped FeS2 porous hollow nanospheres were prepared by solvothermal and subsequent calcination processes.The porous structure facilitates the infiltration of electrolyte,and the successful doping of phosphorous atoms in the material provides more active sites for ions.The hollow structure can better buffer the volume expansion,which is beneficial to the cycling stability of the material.When P-doped FeS2 acted as anode for potassium ion batteries,it can maintain a specific capacity of 150.8 mAh g-1 at 1 A g-1 after 6000 cycles.In addition,potassium ion full cells of P-doped FeS2//PTCDA-450 were successfully assembled and the discharge capacity remained at 111.4 mAh g-1 at 100 mA g-1 after 500 cycles.The synergistic effects between the porous hollow structure design,heteroatom doping and the uniform composite of the carbon material are beneficial for high electrochemical performances in the potassium ion full/half cells.