The Construction And Performance Of Cross-linked Gel Electrolyte/ PPS Non-woven Composite Separator In Lithium-ion Battery

The development of high-power lithium-ion batteries is facing two major challenges: safety issues and battery performance.Although the separator as the "third electrode" of the lithium-ion battery is not involved in electrochemical reaction,it is responsible for protecting the battery and transporting lithium ions.Compared with the traditional polyolefin membrane,the non-woven matrix membrane has a higher porosity and a better thermal stability through the selection of raw materials.Melt-blown polyphenylene sulfide(PPS)non-woven has excellent high temperature resistance,corrosion resistance and flame retardant properties.However,the holes formed by its own fibers are large and uneven,and can only be used as separator after surface modification or coating.Using gel polymer electrolyte as coating is a common method to modify nonwovens,but the gel electrolyte prepared by pure polymer has the defects of low ionic conductivity and poor mechanical properties.In view of this,this study intends to construct a cross-linked gel electrolyte on the surface of melt-blown polyphenylene sulfide non-woven,hoping to reduce the crystallinity of gel electrolyte,regulate the pore structure formed,and promote the adsorption of electrolyte through the introduction of the cross-linked network.In addition,the introduction of cross-linked network will help to enhance the mechanical properties of PPS non-woven based composite membrane.The research contents and achievements of this paper are as follows:Firstly,we have constructed a single cross-linked network gel electrolyte on the surface of PPS non-woven to obtain the cross-linked composite membrane CLN/PPS.Among them,the single cross-linked network is formed by the reaction between hyperbranched polyethylenimine(PEI)and polyvinylidene hexafluorpropylene(PVDF-HFP).Due to the nucleophilicity of the amine group and the strong polarity of the C-F bond,the multi-functional group PEI and PVDF-HFP can have a rapid chemical reaction and form a single cross-linked network structure.It is found that the composite membrane CLN/PPS has improved wettability,high electrolyte uptake,good ionic conductivity and excellent interfacial compatibility,thus reducing the ohmic polarization degree of the battery and increasing the discharge capacity.This is related to the good hydrophilic capacity of hyperbranched PEI and the regulation function of its ellipsoid topology on the crystallinity of PVDF-HFP.In addition,the study shows that the composite membrane can still show good thermal dimensional stability after being treated at 200?.At the same time,it is found that the introduction of 3D cross-linked network can make the composite membrane have enhanced mechanical properties,wide electrochemical window and excellent battery cycling performance.Secondly,we have constructed a semi-interpenetrating network gel electrolyte on the surface of PPS,and obtain the composite membrane SIPN/PPS.Among them,the semi-interpenetrating network is composed of macromolecule polyethylene oxide(PEO),branched PEI and epoxy-terminated polyethylene glycol(PEGDGE).Due to the open-loop reaction between amine group and ethylene oxide,PEI and PEGDGE can form a cross-linked network structure,in which the macromolecule PEO runs through.It is found that the composite membrane SIPN/PPS has a perforating pore structure,good electrolyte uptake,high ionic conductivity and excellent interface compatibility,so that the assembled battery has a good charge-discharge performance.This is related to the introduction of hyperbranched PEI and cross-linked network structure,which can reduce the crystallinity of PEO matrix and regulate its pore-forming performance.At the same time,the composite membrane also has outstanding tensile strength.Compared with the single cross-linked network,the introduction of semi-interpenetrating cross-linked network can enhance the mechanical properties better.In addition,it is found that the introduction of semi-interpenetrating network can also improve the thermal performance of the composite membrane,significantly improve its electrochemical stability and the corresponding battery cycle stability.