Structural Regulation And Performance Research Of Electrospun Nanofiber Composite All-solid-state Electrolyt

Solid-state electrolytes（SSEs）,as the core components of all-solid-state batteries,directly affect the energy density and safety of lithium metal batteries.The low room temperature ionic conductivity of SSEs and the continuous growth of lithium dendrites are the two technical bottlenecks facing the development of high-performance all-solid-state batteries.To solve the above problems,the paper constructs different types of electrospun nanofibers and nanowires based on electrospinning technology from the perspectives of structural design,functional doping and process optimization,and discusses the application of nanofiber-modified polyethylene oxide（PEO）-based composite solid electrolytes（CSEs）.The aim is to develop CSEs that combine high ionic conductivity,strong mechanical strength,and excellent ability to inhibit lithium dendrites growth.The main research contents of this paper are as follows:（1）Polyvinylidene fluoride nanofiber membrane（T-PVDF）with root-like structure was prepared by electrospinning technology,and then composited with PEO polymer to construct a"root-soil"composite solid electrolyte.Benefiting from the existence of the root-like structure,the overlapping of coarse fibers and fine fibers in the fiber membrane can provide a strong skeleton support for the composite electrolyte,thereby enhancing its ability to inhibit the growth of lithium dendrites.The introduction of T-PVDF nanofiber membrane can also significantly reduce the crystallinity of the polymer,thereby accelerating the transport of lithium ions along the PEO molecular chain.（2）In order to further improve the ionic conductivity of the T-PVDF nanofiber membrane composite electrolyte in the previous chapter,this chapter constructs Li_6.4La₃Zr_1.4Ta_0.6O₁₂（LLZTO）anchored T-PVDF composite nanofibers based on blended electrospinning technology,and then introduces it into PEO to obtain composite electrolytes with high ionic conductivity.Benefiting from the dehydrofluorination of PVDF,the interaction between PVDF,LLZTO and lithium salts is enhanced,the optimal ionic conductivity of the composite electrolyte can reach 9.3×10^-4 S cm^-1 at 50 ^oC,and the mechanical strength is further improved to10.3 MPa.The discharge specific capacity and capacity retention rate of the assembled Li Fe PO₄/Li cell after 500 cycles at 1 C are as high as 116.8 m Ah g^-1 and96%,respectively.（3）Considering the limitation of organic nanofibers for lithium ions transport,gadolinium-doped cerium oxide（Ce O₂）（GDC）inorganic ceramic nanowires with abundant oxygen vacancies on the surface were prepared and then composited with PEO.The interaction of abundant oxygen vacancies on the surface of GDC nanowires with anions in lithium salts can increase the concentration of internal carriers in the composite electrolyte,which in turn improves the ionic conductivity of the composite electrolyte to 5×10^-4 S cm^-1（30 ^oC）.Both the assembled Li Fe PO₄/Li and Li Ni_0.8Mn_0.1Co_0.1O₂（NMC）/Li cells exhibited excellent cycling stability.（4）In view of the problem that the mechanical strength of the GDC/PEO composite electrolyte in the previous chapter is still insufficient,this chapter firstly prepares a PVDF-PEO composite lithium ions conductor nanofiber membrane with a core-shell structure based on coaxial electrospinning technology,and then introduced it into PEO polymers simultaneously with GDC nanowires.In addition to the promotion of Li ions transport by GDC nanowires,the core layer PVDF in PVDF-PEO can endow the electrolyte with sufficient mechanical strength to suppress the growth of lithium dendrites,and the shell layer PEO can further provide additional3D ordered transport channels for Li ions.The Coulombic Efficiency of the high-voltage NMC/Li cell assembled with this composite electrolyte can still be maintained at 99.2%after 250 cycles at 0.5 C.