Research On Ultrathin Two-Dimensional Nanosheet Composite PAN-based Lithium Metal Battery Separator

Lithium metal batteries（LMBs）have always attracted attention due to their ultra-high theoretical specific capacity.However,the lithium dendrites generated during cycling of LMBs will consume the electrolyte and cause capacity fading,and in severe cases,puncture the separator and cause safety problems,thus limiting the commercial application of LMBs.In this paper,three kinds of ultrathin two-dimensional nanosheets were used to modify the electrospinning polyacrylonitrile（PAN）fiber membranes to prepare composite membranes that can inhibit the growth of lithium dendrites.Firstly,GO@PAN composite membrane with core-shell structure was prepared by electrostatic spinning combining with electrospraying.Different ratios of graphene oxide（GO）and PAN can be used to prepare composite separators with different morphologies.After characterization,a composite membrane with a more uniform structure was selected for subsequent testing.The test results of the assembled Li/Li Fe PO₄ battery from the GO@PAN composite membrane show that the battery with the composite separator still exhibits a high discharge specific capacity(144 m Ah g^-1)after 300 cycles at a rate of2 C,proving that the separator can be applied potential for longer-cycle lithium batteries.Subsequently,GO was etched with H₂O₂ to obtain porous graphene oxide（HGO）with holes on the sheet.It was composited with PAN by simple suction filtration to obtain HGO-PAN composite fiber membrane.The nanofluidic channels between the pores of the HGO basal plane and the 2D nanosheets can redistribute the flow of Li⁺,thereby regulating the formation and growth of Li dendrites.The as-prepared HGO-PAN separator has high porosity and high ionic conductivity,and the symmetric Li/Li cell with HGO-PAN separator achieves an ultra-long cycle life of 800 h at 1 m A cm^-2.In addition,two-dimensional organometallic framework（MOF）nanosheets,Zn-TCPP,with different morphologies were prepared by adjusting the raw materials,and a Zn-TCPP nanosheet was selected for compounding with PAN.The good affinity between the Zn-TCPP/PAN composite membrane and the electrolyte enables it to exhibit high ionic conductivity(2.05 m S cm^-1).The assembled Li/Li Fe PO₄ half-cell still maintains a high discharge specific capacity of 117 m Ah g^-1（10 C）.When assembled into a Cu/Li half-cell,it exhibits a stable Coulombic efficiency of 97%after 75 cycles at a current density of 1 m A cm^-2.