Structural Design And Performance Study Of Sulfonated Polyethersulfone Nanofiber Composite Solid Electrolyte

Solid polymer electrolytes are currently one of the important research directions in all solid-state lithium batteries due to their excellent flexibility,thermal stability,good interfacial compatibility,and ease of processing.However,the characteristics of polymer electrolyte such as low ionic conductivity at room temperature,poor mechanical strength and easy to be damaged by lithium dendrite hinder its practical application in all-solid-state lithium metal batteries.In order to solve these problems,in this paper,from the perspective of structural design,functional doping and process optimization,different structures of sulfonated polyether sulfone（SPES）fibers and functional ceramic nanowires are prepared by electrospinning technology to modify polyethylene oxide（PEO）based solid electrolytes,so as to improve the ionic conductivity,mechanical strength and the ability to inhibit lithium dendrites of the solid electrolyte,thereby achieving excellent cycling performance and outstanding safety performance of lithium metal batteries.The specific experimental contents are as follows:（1）Firstly,SPES nanofiber membranes were prepared using electrospinning technology,and the effects of the mass fraction of the spinning solution,spinning voltage,and receiving distance of the electrospinning process on the fiber morphology were investigated.Subsequently,the fiber membrane with the best morphology obtained by the optimal process was combined with PEO-LITFSI solution to obtain a sulfonated polyethersulfone fiber membrane based composite solid electrolyte.The test results showed that SPES membranes containing a large number of fibers can significantly reduce the crystallinity of the PEO matrix.And various nanofibers crisscross each other to form a stable and intersecting support network,enabling the prepared composite solid electrolyte to obtain excellent mechanical properties（4.8MPa）while possessing enhanced ionic conductivity(30℃,6.92×10^-5 S cm^-1).Finally,through theoretical calculations based on the first principle calculations,it is known that the prepared SPES had an adsorption energy of-5.7203 e V for lithium ions,which proved that SPES nanofibers can become jumping sites for the transport of lithium ions.（2）Secondly,in order to further improve the electrochemical performance of SPES nanofiber composite PEO based solid electrolyte,dendritic SPES nanofiber membranes and double layered SPES-（polyvinylidene fluoride hexafluoropropylene）（SPES-PVDF-HFP）fiber membranes were prepared using electrospinning technology.And two kinds of composite solid electrolytes were constructed by pouring PEO-LITFSI solution onto the fiber membranes.It was found that dendritic SPES fibers enabled the PEO matrix to obtain a large area of amorphous regions by means of multi-level branched fibers,improving the ionic conductivity(30℃,8.12×10^-5 S cm^-1)of the composite solid electrolytes.Benefiting from the excellent mechanical strength of PVDF-HFP fiber membrane,the double-layer SPES-PVDF-HFP fiber membrane made the prepared composite solid electrolyte exhibit strong resistance to lithium dendrites.The lithium ion migration numbers of the composite solid electrolyte containing dendritic SPES fibers and double layer SPES-PVDF-HFP fibers at 50℃were 0.48 and 0.46,respectively.And the Li/Li symmetric battery assembled with the composite solid electrolytes operated stably for 800 h and 900 h at 50℃and0.2 m Ah cm^-2,respectively.（3）Furthermore,LaCoO₃ nanowires with Lewis acid sites and oxygen vacancies on the surface were obtained through electrostatic blowing technology and calcination method.Then,it was poured on dendritic SPES fiber skeleton as filler of PEO solution to prepare a kind of rigid and flexible composite electrolyte.LaCoO₃nanowires with Lewis acid sites and oxygen vacancies on the surface released a large number of free lithium ions which transported along the ion transport path constructed by SPES fiber and LaCoO₃ nanowires,making the prepared composite solid electrolyte exhibit an ionic conductivity of 1.86×10^-4S cm^-1at 30℃.And mechanical strength of electrolyte can be increased to 6.3 MPa.The initial specific capacity of the pouch cell composed of prepared electrolyte and Li Fe PO₄/Li can reach 143.9 m Ah g^-1at 60℃and 0.15 C.（4）Finally,in order to evenly penetrate 1D LaCoO₃ nanowires into the entire solid state electrolyte and construct a continuous 3D organic-inorganic ion transport pathway,SPES and PEO composite fiber membranes（C/SPES-PEO）with 3D crimped structure were prepared using parallel electrospinning technology.The 3D crimped structure gave C/SPES-PEO fiber membranes a large pore structure,effectively achieving the effective penetration of functional ceramic nanowires throughout the entire composite solid electrolyte.Therefore,the ionic conductivity of the constructed electrolyte can reach 2.5×10^-4S cm^-1 at 30℃,the mechanical strength was further increased to 7 MPa.And the Li Fe PO₄/Li pounch cell prepared by electrolyte can maintain a capacity retention of 87%after 150 cycles at 60℃and 0.2C.In order to explore the specific mechanism of ion transport by C/SPES-PEO fibers and LaCoO₃ nanowires,the adsorption of LITFSI by LaCoO₃ was calculated using density functional theory calculations.The highest transfer rates of lithium ions at the interfaces of SPES/LaCoO₃ and PEO/LaCoO₃ were confirmed to be 1.46×10^-4 cm²s^-1and 1.05×10^-4 cm²s^-1 through nudged elastic band（NEB）calculations.In addition,in order to demonstrate the universal applicability of the characteristic of C/SPES-PEO fiber membranes,Gd doped Ce O₂（GDC）nanowires were also replaced with LaCoO₃nanowires to explore the performance of composite electrolytes.The prepared lithium batteries also exhibited excellent cycle performance.