Synthesis And Sodium Storage Performance Of Carbon/Transition Metal Chalcogenide Composite Nanosheets Based On Oriented Attachment Mechanism

Transition metal chalcogenides as anode materials of sodium ion batteries have the advantages of friendly environment,wide sources and high specific capacity.But they also have the disadvantages of volume expansion and poor sodium storage kinetics,which limits their practical application.Designing special nano-structured transition metal chalcogenide/carbon composites can effectively improve electrochemical performance of the materials.In this work,aiming at the above problems,an in-situ pyrolysis method based on oriented attachment mechanism was used to synthesize the carbon coated transition metal chalcogenide two-dimensional(2-D)nanocomposite with core-shell structure.The unique microstructure of the composites endows them with excellent sodium storage performance.The main contents summarized as follows:(1)Carbon coated Fe2S8 composite nanosheets(Fe7Ss@CNS)with a thickness of 5 nm were synthesized using elemental sulfur and ferrocene.The ultrathin 2-D core-shell structure greatly improved the diffusion kinetics of Na+.When used as anode material,Fe7S8@CNS nanosheets exhibited excellent rate performance and cyclic stability in ester-and ether-based electrolyte:At 100 mA g-1,its specific capacity was as high as 540.7 mA h g-1.When the current density increased to 20 A g-1 and circulated 8000 times,the specific capacity could still be maintained at 170 mA h g-1.(2)The microflower-like materials assembled by carbon coated FeSe nanosheets(FeSe@CNS)were synthesized by using SeO2 and ferrocene as raw materials.The three-dimensional structure assembled by 2-D core-shell nanosheets inhibited the volume expansion of FeSe,enhanced the diffusion ability of Na+,and improved the structural stability of materials.The high-crystallinity FeSe@CNS exhibited ultrahigh initial coulombic efficiency(99.8%),high specific capacity(460.2 mA h g-1),good rate and cycle stability when used as anode material for sodium ion batteries.At 30 A g-1,the reversible capacity was close to 100 mA h g-1 after 10000 cycles.The FeSe@CNS could be matched with cathode material without presodiation and assembled into a full battery.The specific capacity of the full battery at 1 A g-1 was 216 mA h g-1,without attenuation after 140 cycles,showing excellent practical application potential.