Study On Preparation And Modification Of Acrylate-based Gel Polymer Electrolyte

The need for energy density and safety performance makes it more and more difficult for traditional lithium-ion batteries using liquid electrolytes to meet the requirements.Researchers gradually turned their attention to solid-state lithium-ion batteries.Compared with traditional lithium-ion batteries,solid-state lithium-ion batteries have excellent safety performance due to the use of solid electrolytes as separators and electrolytes.In extreme cases such as thermal runaway and puncture,it will not catch fire.The core requirements for solid electrolytes are to have the wide electrochemical window,a high lithium ion migration number,ideal ionic conductivity,low electronic conductivity,flame retardancy and sufficient mechanical properties.Acrylate-based gel polymer electrolyte is one of the more ideal ones,especially the in-situ polymerization technology inside the battery solves the biggest scientific problem of the electrode-electrolyte interface that plagues solid-state lithium-ion batteries.In this paper,the PEGDA-based gel polymer electrolyte was prepared by in-situ thermal polymerization,and a high-performance composite electrolyte was modified based on this.And combinated with Li Fe PO₄ and CNT/S cathode for charge and discharge tests,the main research contents of this article are as follows:（1）A gel polymer electrolyte formed by cross-linking and polymerization of PEGDA and ETPTA monomers to form a 3D network structure by thermal polymerization.The internal network structure provides a rich channel for lithium ion transfer.The effect of monomer volume ratio on the electrochemical performance of electrolyte was discussed.When the PEGDA:ETPTA=6:1 monomer volume ratio is obtained,the gel polymer electrolyte has the highest ionic conductivity,reaching 8.7×10^-4 S cm^-1 at room temperature and has an electrochemical window exceeding 4.2 V.Its lithium ion migration number is as high as 0.71.（2）GPE6 with the best electrochemical performance was selected,two kinds of batteries were manufactured by in-situ thermal polymerization and lamination assembly method inside the battery,and the advantages and disadvantages of the two preparation methods were discussed.The SEM characterization and EIS analysis of the lithium metal anode surface after cycling are used to illustrate the advantages of the in-situ thermal polymerization method in the battery compared to the lamination method at the electrode-electrolyte interface.The initial discharge specific capacity of LFP|S-GPE|Li battery is close to 140 m Ah g^-1 at 0.2 C current density,and the capacity retention rate is 90.9%after200 cycles;the initial discharge specific capacity at 1 C current density has reached 124.4m Ah g^-1,after 200 cycles,the capacity retention rate is 76.6%,reflecting the excellent cycle performance.（3）A composite gel polymer electrolyte in which PEGDA polymer matrix and LLZTO nano-ceramic particles with uniform thickness can be uniformly mixed is prepared by in-situ thermal polymerization.After a series of physical and chemical characterization and electrochemical tests including EIS and LSV,the optimal mass fraction of LLZTO particles was discussed.The CPE50 with the best overall performance is obtained,which has an ion conductivity of 1.34×10^-3 S cm^-1 and an electrochemical window of 4.6 V.Through the analysis and interpretation of the Lewis acid-base theory,it is found that LLZTO powder as the Lewis acid provides the rich coordination point for the Lewis base.And based on the Lewis acid-base effect,LLZTO can strongly interact with the TFSI^-anion.Thereby further limiting the diffusion of TFSI^-anions achieves a lithium ion migration number of up to 0.72.At the same time,CPE50 has a significant inhibitory effect on the polysulfide shuttle in Li-S batteries,as well as excellent flame retardancy and thermal stability.The Li-S battery assembled from CPE50 was charged and discharged at 1 C current density.The specific discharge capacities after the first cycle and the 200th cycle were 1201 m Ah g^-1 and 656 m Ah g^-1,respectively,and the capacity retention rate was 54.6%.