Research On The Structure Design Of Metal Oxide/sulfide Material And Its Lithium Storage Performance

Due to the environmental problems caused by the use of fossil energy,lithium ion batteries?LIBs?,as a typical secondary battery,are engaging more and more attention because of its advantages of high energy density,long cycle life for various electronic devices,as well as application in electrical vehicles.Graphite,the currently used commercial anode,cannot meet the demand of future high energy density LIBs due to its low theoretical capacity of 372 mA h/g.Compared with Graphite,metal oxides and metal sulfides as anodes have a much larger capacity.However,the volume expansion and shrinkage in the lithiation/delithiathion process,resulting in severe decrease in stability of structure and conductivity,leads to decline of capacity during cycling.Therefore,it is of urgent need to develop new electrode materials with higher energy capacity.Herein,to address the problems existing in lithium ion batteries anode materials,we proposed rational design strategies to synthesize four kinds of nanocomposites as anode materials,and studied the structure-property relationships.?1?Nanocomposite of graphene/?-Fe₂O₃?G/?-Fe₂O₃?nanospindles was synthesized by a simple hydrothermal assembly method followed by thermal treatment.The?-Fe₂O₃nanospindles were evenly enwrapped by the graphene nanosheets.When evaluated as an anode for Li-ion batteries?LIBs?,G/?-Fe₂O₃ nanocomposite showed enhanced cycling performance and rate capability compared to pure?-Fe₂O₃.G/?-Fe₂O₃ retained a reversible capacity of 607 mA h g^-1 after 100 cycles at 100 mA g^-1,which is far higher than that(160mA h g^-1)of?-Fe₂O₃.The superior electrochemical performance of G/?-Fe₂O₃ can be attributed to the protection effect of graphene nanosheets to accommodate the volume change of?-Fe₂O₃ during lithiation/delithiation.?2?A strong interface coupling is of vital importance to develop metal oxide/carbon nanocomposite anodes for next-generation lithium ion batteries.The PPy microtubes were synthesized through a template-engaged in-situ polymerization process,and then grow FeOOH nanoparticles by hydrothermal method.Polypyrrole?PPy?has been used as the precursor for N-doped carbon.N-doped carbon-riveted Fe₃O₄/N-doped carbon?N–C@Fe₃O₄@N–C?nanocomposites were obtained by pyrolysis of PPy-coated FeOOH@PPy nanotubes in Ar atmosphere.When tested as an anode for LIBs,the N–C@Fe₃O₄@N–C displays a high reversible discharge capacity of 675.8 mA h g^-1 after 100 cycles at a current density of 100 mA g^-1?3?Micro/nanostructures consisting of different density of MoS₂ nanosheets vertically grown on N-doped carbon microtubes?NCMs?are rationally designed by a facile solution approach.NCMs was selected as the support to prevent aggregation of MoS₂ nanosheets,and serve as the pathway for electron conduction,as well as a media to alleviate the volume change of MoS₂ during lithiation/delithiation.Due to the advantageous structure,the MoS₂@NCMs show significantly enhanced lithium storage properties in comparison to pure MoS₂.?4?A unique lamellar architecture of N-doped carbon coated SnS/graphene?NC/SnS/G?nanocomposites is designed by a combined process involving hydrothermal synthesis,chemical polymerization and post annealing in Ar.It is found that N-carbon/SnS/graphene nanosheets deliver a high reversible capacity of 840 mA h g^-1 after 150 cycles at a current density of 100 mA g^-1 and higher rate properties in comparison to SnS/graphene.The improved electrochemical performances are attributed to the special lamellar structure with a combined synergic effect derived from the N-carbon coating layers and graphene nanosheets.