Preparation Of Carbon-based Layered Iron Sulfide Quantum Dot Composite Nanosheets And Their Performance As The Host Materialof Sodium Metal Anode

Due to its wide range of sources,low price and high theoretical specific capacity,sodium metal anode is expected to become an ideal anode for next-generation rechargeable batteries.However,the challenges caused by itself chemically active of Na metal,huge volume change during sodium plating/stripping process and dendrite growth on Na metal anode have hindered the further application of sodium metal batteries.In this paper,carbon-based layered iron sulfide quantum dots composite nanosheets(Fe7Ss@CNS)was obtained by a one-step in-situ pyrolysis method.Based on an Oriented Attachment(OA)growth mechanism,iron sulfide quantum dots with a size of 2-3nm are evenly distributed in the carbon matrix and assembled into a two-dimensional layered superlattice structure.Fe7S8@CNS as the host of anode electrode for a sodium metal battery exhibits a dendritic-free morphology and good electrochemical performance.At the conditions of 2 mA cm-2 and 2 mAh cm-2,the half battery can cycle up to 1000 cycles at a high coulombic efficiency(CE)of?99.8%.Even at the conditions of 3 mA cm-2 and 3 mAh cm-2,the Fe7S8@CNS anode electrode host material can stably circulate 500 cycles with a CE as high as-99.5%.And the symmetrical battery can run stably for 700 hours under the conditions of 2 mA cm-2 and mAh cm-2.In addition,the full battery assembled by Na@Fe7Sg@CNS anode and sodium vanadium phosphate(Na3V2(PO4)3)cathode has excellent rate performance and cycle life.At the current density of 1A g-1,the full battery can be charged and discharged 1000 times with a specific capacity of 88.0 mA hg-1.The good electrochemical performance of Fe7S8@CNS as the host of the sodium metal anode is mainly due to its unique structure.Ultra-fine Fe7S8 quantum dots can significantly reduce the nucleation barrier of sodium metal and guide the uniform nucleation of sodium metal,thereby avoiding the growth of sodium dendrites.The layered structure 'of the quantum dots assembly can effectively relieve the stress caused by the volume change of sodium during the plating/stripping process.The carbon layer blocks the direct contact between the electrolyte and quantum dots,thereby preventing the quantum dots from agglomerating and being stripped by the electrolyte during the cycle and making quantum dots have long-cycle cycle stability.The design of carbon-based layered iron sulfide quantum dots composite nanosheets has opened up a new avenue for the development of dendritic-free sodium metal anode.