Preparation Of Transition Metal Sulfides Anode Materials And Prussian Blue Analogues Cathode Materials And Their Electrochemical Performance

With the rapid development of modern industries and serious pollution caused by fossil fuels,rechargeable batteries have attracted researchers'attention because of their high energy density,admirable energy conversion efficiency and flexibility.At present,lithium ion batteries?LIBs?have already been commercialized while the shortage of lithium resource limited their further development.Considering the natural abundance of sodium resource and the similar physiochemical properties between sodium and lithium,many researches about sodium ion batteries?SIBs?are carried out on the basis of LIBs,aiming to make SIBs as alternatives for LIBs in large-scale energy storage.Based on the“rocking-chair”working principle,it is the key to design electrode materials with high specific capacity,superior electron/ion conductivity and long cycle life for the development and application of LIBs/SIBs.Transition metal sulfides?TMSs?and Prussian blue analogues?PBAs?are characterized by rich abundance,various structures and environmental friendliness,showing high energy density and good electrochemical stability as electrodes.Furthermore,fabricating composites with carbonaceous materials can effectively buffer volume changes of TMSs during charging/discharging,and controlling the species and chemical environment of transition metal ions in PBAs will decide the electrochemical properties.Herein,we studied TMSs anode materials and PBAs cathode materials,including materials preparation,composition control,structural and morphological characterization,and electrochemical measurements.Two research parts are following:?1?Flexible and freestanding TMSs are usually fabricated by electrospinning,while sulfuration often destroys the flexibility of membrane and choosing suitable precursor is tough.Flexible and freestanding transition metal sulfides@carbon nanofibers composites are fabricated by adopting L-cysteine in this work.Using FT-IR technique,we reveal the formation mechanism and prepare a series of such composites,including SnS/C,Fe₇S₈/C and Ni₂S₃/C.They all have three-dimensional network structure,which is interwoven by nanofibers with TMSs nanoparticles uniformly dispersed in.Such unique structure leads to superior flexibility,restrains the volume expansion of TMSs and provides intact conductive network,making such composites exhibit superior electrochemical lithium/sodium storage properties.Take SnS/C as an example,its specific capacity reaches 812.7 mAh g^-1 and 327 mAh g^-1 for lithium/sodium storage at 50 mA g^-1;for lithium storage,the specific capacity remains403.9 mAh g^-1 after 400 cycles at 1 A g^-1;for sodium storage,the specific capacity remains 330.4 mAh g^-1 after 100 cycles at 50 mA g^-1.?2?The general formula of PBAs is A_xM[M'?CN?₆]y·nH₂O.The bond length of M'-C bond greatly influences lattice parameters and channel sizes.The species and valence states of transition metals are essential to electrochemical performance.In this work,various types of PBAs are prepared through coprecipitaion method.With different the coordination structures of Co and Fe,Na_xCo[Fe?CN?₆]and K_xFe[Co?CN?₆]nanoparticles show similar morphologies of well-defined nanocubes.Sodium storage performance and oxygen evolution?OER?performance are systematically characterized.Due to the difference of M-CN-M',the first discharge capacities of Na_xCo[Fe?CN?₆]cathode and K_xFe[Co?CN?₆]anode reach 104.1 mAh g^-1 and 354.8 mAh g^-1.The full cell of Na_xCo[Fe?CN?₆]?SnS/C exhibits higher output voltage compared with the full cell of Na_xCo[Fe?CN?₆]?K_xFe[Co?CN?₆].Its first reversible specific capacity reaches to 317.5 mAh g^-1 based on the mass of anode.Furthermore,Na_xCo[Fe?CN?₆]shows better OER performance and we study the influence of chemical component and heat treatment in OER performance of PBAs.The OER performance gradually decreases from Na_xCo[Fe?CN?₆],Na_xNi[Fe?CN?₆]to K_xNi[Co?CN?₆].With the increase of temperature,the OER performance of Na_xCo[Fe?CN?₆]continues falling while that of Na_xNi[Fe?CN?₆]first falls then rises and that of K_x Ni[Co?CN?₆]continues rising,which is due to the destruction of structure and the formation of metal oxide.