Synthesis,characterization And Lithium Storage Properties Of ZnMnO₃-based Anode Materials For Lithium Ion Batteries

At present,new energy vehicles have become the development demand of the society.Lithium ion batteries?LIBs?,due to its light weight,small self-discharge,high energy density,no memory,high working voltage,low environmental pollution and so on,have attracted much attention.Transition metal oxide ZnMnO₃?ZMO?,as an anode material for LIBs,has become the research object of many researchers thanks to its high theoretical capacity(1117 mAh g^-1),abundant reserves and cost/environment-efficiency.The current challenge is that ZMO has poor conductivity and volume expansion during the charging and discharging processes,affecting the rate properties and cycling stability.In this thesis,we focus on the structural design and controllable synthesis of ZMO with the final aim to reduce the volume variation and improve the electrochemical properties.The detailed research contents of the thesis are described as follows:?1?We devised a scalable bottom-up methodology for fine fabrication of hollow mesoporous ZnO/ZnMnO₃?ZZMO?microspheres.It is found that the hollow mesoporous ZZMO microspheres,which are bi-component-active ZnO and ZMO hetero-structure at the nanoscale,are fabricated of countless nanoparticles with the size of 12 nm.The excellent lithium storage properties of hollow mesoporous ZZMO microsphere structure are attributed to reducing the diffusion length for lithium ion?Li⁺?and tolerating the volume variation during the Li⁺insertion/exsertion,thus enhancing the structural integrity.The hollow ZZMO microspheres are endowed with the discharge capacity of 1045 mAh g^-1 after 350 cycles at 0.5A g^-1,as well as the reversible capacity of 695 mAh g^-1 at 1.0 A g^-1 after 500 cycles.Moreover,the ZZMO microsperes can still present the reversible capacity of 415 mAh g^-1 at a high current density of 3.0 A g^-1.Therefore,these results highlight that the hollow mesoporous ZZMO microspheres present the stable cycling performance and remarkable rate capability.?2?PPY@ZMO micron pieces were obtained by solvothermal method,calcination and subsequent chemical polymerization method.The study found that polypyrrole?PPY?layer with the thickness of 1.9 nm is in situ deposited on the surface of ZMO micron pieces.The coating of PPY can enhance the conductivity,buffer the volume variation during the charge and discharge processes and prevent the aggregation and pulverization of nanoparticles.PPY@ZMO micron pieces demonstrat that the first discharge capacity is 1045 mAh g^-1 at the current density of 0.5 A g^-1,corresponding 66%of the initial coulombic efficiency,moreover,its reversible capacity can still be maintained at 1038 mAh g^-1 after 250 cycles,when cycled at a current density of 2 A g^-1,which appears the reversible capacity of 752.0 mAh g^-1.Therefore,PPY@ZMO micron pieces exhibit the excellent cyclic performance and rate properties.?3?One-dimensional?1D?porous ZMO nanorods were synthesized by a simple coprecipitation and subsequent calcination method.1D porous ZMO nanorods with large specific surface area ensure the effective contact of the electrolyte to the electrode surface,providing more electroactive sites.The pores in 1D ZMO nanorods are usually continuous,which offers interconnected ion diffusion pathways and shortens the ion diffusion length.The empty spaces in porous nanostructures accommodate the volume changes associated with electrochemical reactions during cycling.The discharge capacity of one-dimensional porous ZMO nanorods can still be stabilized at 949.7 mAh g^-1 after 500 cycles under the current density of 0.5 A g^-1.When the current density increased to 2.0 A g^-1,the reversible capacity can present 454.3 mAh g^-1.The results directly show that the 1D porous ZMO nanorods exhibit the superior electrochemical lithium storage performance.